WO2006030413A2 - Method and apparatus for mapping a retina - Google Patents

Method and apparatus for mapping a retina Download PDF

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Publication number
WO2006030413A2
WO2006030413A2 PCT/IL2005/000942 IL2005000942W WO2006030413A2 WO 2006030413 A2 WO2006030413 A2 WO 2006030413A2 IL 2005000942 W IL2005000942 W IL 2005000942W WO 2006030413 A2 WO2006030413 A2 WO 2006030413A2
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WIPO (PCT)
Prior art keywords
illumination
gate
source
light
retina
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PCT/IL2005/000942
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French (fr)
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WO2006030413A3 (en
Inventor
Gavriel J. Iddan
Avishai J. Friedman
Giora Yahav
Shlomo Azar
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3Dv Systems Ltd.
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Publication of WO2006030413A2 publication Critical patent/WO2006030413A2/en
Publication of WO2006030413A3 publication Critical patent/WO2006030413A3/en

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
    • A61B3/14—Arrangements specially adapted for eye photography

Definitions

  • the present invention relates in general to imaging of the eye, and in particular to the morphological three-dimensional imaging of the retina of the eye.
  • an eye-care specialist may take advantage of any of the three most prominent existing retinal diagnostic tools, which are the fundus camera, the Optical Coherence Tomograph, and the Heidelberg confocal microscope.
  • the fundus camera takes two-dimensional images only, and therefore lacks the three-dimensional imaging capability that is so important to an eye-care specialist for diagnostic purposes.
  • the Optical Coherence Tomograph is able to provide optical biopsy, which is a detailed description of the retina layer structure, similar to the information retrieved by classical microscope biopsy.
  • the Optical Coherence Tomograph does not present a complete 3D-model and the equipment is rather onerous, thus affordable only to large medical facilities.
  • the Heidelberg confocal microscope uses scanning techniques to derive details of the retinal layers, which scanning procedures are inherently time consuming. Furthermore, the Heidelberg confocal microscope has the disadvantage of being an expensive device.
  • US Patent No. 5,220,360, to Verdooner et al. disclose "An apparatus and method for topographically mapping an internal ocular surface, including projection means for projecting a plurality of parallel lines onto the internal ocular surface in a specified line orientation and with a specified direction of projection, camera means for capturing an image of the internal ocular surface having parallel lines projected thereon, the image being captured at an angle from the direction of projection, and means connected to the camera means for generating digital picture element data representative of the image of the internal ocular surface and for identifying the picture element locations of images of the parallel lines in the image and for generating a topographical map of said internal ocular surface based on imaged curvatures of the projected parallel lines, and comparison means associated with the computer means for retrieving at least one of the types of previously stored data relating to said internal ocular surface and then comparing a first topographical
  • Verdooner et al. do not use single shot illumination of the field of view and do not operate a Shack-Hartmann device in association with fast gating.
  • Wirth describes "An ophthalmic instrument comprising: a wavefront sensing illumination source producing light that is formed as a spot image on the retina of the human eye and reflected there from; and a wavefront sensor that estimates aberrations in reflections of the light formed as a spot image on the retina of the human eye, wherein the wavefront sensor comprises a beam splitter operably disposed between a lenslet array and multiple imaging devices, said lenslet array forming a first array of spots, and said multiple imaging devices capturing multiple images of said first array of spots for use in estimating said aberrations.”
  • the wavefront sensor comprises a beam splitter operably disposed between a lenslet array and multiple imaging devices, said lenslet array forming a first array of spots, and said multiple imaging devices capturing multiple images of said first array of spots for use in estimating said aberrations.”
  • Wirth measures aberrations.
  • RTA retinal thickness measurement instrument
  • the prior art dealing with the imaging of the retina does not disclose a "one shot” area illumination of the whole field of view, and furthermore, does not use a gated Shack-Hartmann diagnostic apparatus for providing a three dimensional (3D) morphological image of the retina of an eye under examination, as with the present invention. It would thus be advantageous to provide the eye-care specialist community with a real time Retinal Imager, or RI, for topographically mapping an internal ocular surface, that is simple, low cost, fast operating and three-dimensional, affordable to small clinics and to practitioners for use in their offices.
  • RI retina imager
  • the problem consists of the need to provide the eye-care specialist community with a simple, low cost method and an apparatus for the real time imaging and 3D topographical mapping of an internal ocular surface.
  • the solution is provided by a method and an apparatus operating a source of light-flash illuminations on the examined eye wherefrom reflected light is returned.
  • the reflected light carries a first reflection returned from the front portion of the eye, i.e. from the cornea and from the lens, and a second reflection returned from the retina.
  • the first reflection must be deleted, which is achieved by the help of a fast gate being disposed on the optical path of the reflection from the eye.
  • the fast gate remains closed to block the first reflection and is opened for passage of the second reflection, which is directed onto a detector, via a Shack- Hartmann device.
  • Data derived by the Shack-Hartmann device is forwarded the detector for data collection, and to a processing unit coupled to the detector.
  • the Shack-Hartmann device is then operated separately in the conventional way to provide eye aberrations measurements, which are forwarded to the processing unit and are used to correct the second reflection.
  • the second reflection is now the desired net reflection from the retina.
  • Illumination with different wavelengths permits to map corresponding layers of the retina. For example, simultaneous illumination in three different wavelengths will send radiation to penetrate into three different layers of the retinal tissue. A 3D morphology of the retina is thus obtained in real time.
  • Images derived by the processing unit are displayed on one or more monitors, in monochrome and in color, alone and in superposition, before or after further image processing.
  • a source of illumination is directed onto the retina, creating reflections returned from the eye.
  • a Shack-Hartmann device is used for receiving reflections returned from the eye, and for transmitting information derived from the received reflections.
  • an image sensor is employed for capturing reflections received via the Shack-Hartmann device, and for emitting signals derived from the captured reflections.
  • a processing unit is coupled to the image sensor, for receiving data from the image sensor, and for processing and delivering processed data.
  • the source of illumination is triggered to emit at least one pulse of light as a flash lasting for a predetermined duration of time.
  • the fast gate is opened into a first open state and closed into a second closed state in predetermined synchronization with the at least one pulse of light, and the processing unit is operated to derive a retina map from the data received from the image sensor via the fast gate.
  • a source of illumination configured to emit light such as invisible light, visible light, coherent light, white light, infrared light, and/or ultraviolet light.
  • the source of illumination may be triggered to emit a sequence of pulses of light including at least one selected wavelength, or at least two different wavelengths, or more wavelengths.
  • each at least one pulse of light is limited to a duration short enough to ensure that a second reflection returned from the eye as a retinal reflection will reach the gate after termination of a first reflection returned from the eye as a first reflection from the cornea and from the lens, to permit time domain discrimination between the first reflection and the retinal reflection, where a driver is coupled to the gate and to the source of illumination for synchronization of mutual operation of the gate and of the source of illumination, and the driver controls the gate to remain in the closed state and to deny passage of each one first reflection pulse, and then controls the gate to open from the closed state into the open state and to permit passage of each one of the second reflection pulses being reflected from the retina, whereby the image sensor receives only second reflection pulses reflected from the retina. It is yet one more object of the present invention to provide the s Shack-
  • Hartmann device operated to derive aberration measurement of the cornea and of the lens of the eye under examination, and where the processing unit is configured to correct each one of the second reflection pulses for aberration due to the cornea and to the lens by help of the derived aberration measurement, whereby the processing unit which is coupled to a monitor provides net retina reflection data derived from the second reflection pulses which are corrected for eye aberration.
  • a total reflection prism to be disposed to receive and transmit reflections returned from the eye, and to be configured to deflect the received reflections into three separate channels, each channel out of the three channels being oriented in one direction different from the direction of the other two channels, and each channel carrying only one single wavelength different from the wavelength of the other two channels, each channel operating a separate aggregation of equipment aligned along the direction of the respective channel, the equipment including at least one of each a Shack-Hartmann device, a pinhole filter, a gate selected to match the wavelength of the respective channel, and an image sensor, a driver being coupled to each one gate out of the three channels and to the source of illumination for synchronization of mutual operation of the three gates and of the source of illumination, and for triggering the source of illumination to emit the at least one pulse of light in repetitive succession, and the processing unit being coupled to each one of the three image sensors and to a monitor, whereby images derived from the retina in real time in three different wavelengths are displayed
  • FIG. 1 is a diagram of a first embodiment 100 of a retinal imager
  • Fig. 2a depicts an example of signals derived from a flat wave front
  • Fig. 2b shows an example of signals derived from a morphology imprinted wave front
  • Fig. 3 illustrates the analysis of the an imprinted wave front
  • Fig. 4 depicts the synchronization of the windowing process
  • Fig. 5 illustrates focusing on the retina for calibration purposes.
  • Fig. 6 is a diagram of a second embodiment 200 of a retinal imager
  • Fig. 7 depicts an illumination source with multiple illumination wavelengths
  • Fig. 8 is a diagram of a third embodiment 300 of a retinal imager
  • Fig. 9 is a diagram of a fourth embodiment 400 of a retinal imager. Best Modes for Carrying out the Invention
  • the present invention is of a system and a method for providing a three dimensional (3D) morphological image of the retina of the eye.
  • the Retinal Imager measures, and later reconstructs, a wave front of light directed toward and then reflected by the retina.
  • a high-speed shutter for fast gating is operated to "window" the reflected wavefront so as to extract only a wavefront imprinted with signals reflected from the retina.
  • a Shack-Hartmann lenslets array is operated to receive the imprinted wavefront and to transmit information derived therefrom to an imaging device, and a processing unit calculates results.
  • the results which are displayed on a monitor, are provided as a 3D morphological image of the retina of the eye under examination.
  • Fig. 1 illustrates a diagram of a first embodiment 100, of a Retinal Imager, or RI, for the 3D morphological imaging of the retina R of an eye 11 illuminated by a source of radiation S.
  • a beam of light 13 emitted by the source S, a lens 15, and a first beam splitter 17 are all oriented along an optical axis co-linear with an x-axis of Cartesian coordinates.
  • the lens 15 is disposed for translation in both directions along the x-axis, as shown by the double-headed arrow AA 5 to permit focusing of radiation as desired.
  • the beam of light is of any desired visible or invisible wavelength of light, but is preferably infrared (IR) radiation.
  • Possible sources of light are laser light, provided by Laser Diodes (LD), Laser Emitting Diodes (LED), or laser light provided by optical fibers.
  • LD Laser Diodes
  • LED Laser Emitting Diodes
  • the emitted beam is a train of successive flashes of light, each flash lasting for less than one nanosecond.
  • the source of radiation S is coupled to and controlled by a processor-operated driver 21, operating as a source modulator for modulating the source of radiation S.
  • the driver 21 modulates the radiation to alternately block and unblock or alternately activate and deactivate the beam of light 13.
  • the driver 21 is referred to as a modulator in the incorporated patents referred to hereinabove.
  • the driver 21 has a trigger, not shown in the Figs, for the sake of simplicity, for triggering the source of radiation S to deliver the beam of radiation 13.
  • the beam 13 is directed to pass through the lens 15, to create an illuminating wave front 19 propagating parallel waves.
  • the wave front 19 reaches the first beam splitter 17, taken as the origin O of the system of Cartesian coordinates, from where it is deflected in perpendicular to the x-axis, and oriented along a main optical axis, which is the z-axis.
  • the incoming deflected wave front 23 is now directed to impinge on the eye 11 under examination.
  • the incoming wave front 23 When directed to impinge on the eye 11, along the negative portion of the z- axis, the incoming wave front 23 first crosses the cornea CRN and then the lens LNS, which focuses the beam of radiation on the center 113 of the eyeball 111, thus in the vitreous body VB, to illuminate the retina R.
  • the lens 15 is configured for translation in both directions along the x-axis, as indicated by the double-headed arrow AA. Translation of the lens 15 permits to focus the incoming wave front 23 as desired in the interior of the vitreous body VB, when desired, also on the retina R itself as indicated by RF in Fig. 1.
  • the incoming wavefront 23 is also reflected by the cornea CRN and by the lens LNS. Furthermore, when the imprinted wavefront 25 exits the eye 11, aberrations due to passage via the cornea CRN and the lens LNS are added to the reflected radiation.
  • the imprinted wave front 25 is reflected in a direction opposite to the incoming impinging radiation, and crosses a second focusing lens 27, which is focused on a spatial pinhole filter 29, for eliminating stray light beams.
  • the pinhole of the spatial pinhole filter 29 has a diameter of 0.5 mm. From the pinhole 29, radiation is collimated as a parallel beam 33, via a collecting lens 31, toward a Shack-Hartmann device 35.
  • the Shack-Hartmann device 35 has an input surface 37 covered with an array of lenslets 41, an output surface 39, and is commonly used for measuring optical aberrations of the eye. With the present invention, the Shack-Hartmann 35 device is operated both as a tool for mapping the topography of the surface of the retina R and in the conventional manner for the measurement of the optical aberrations of the eye. It is noted that the operation of the Shack- Hartmann device 35 is independent of the wavelength of the light used therewith, but is solely dependent of the properties of propagation of light.
  • Shack-Hartmann lenslets array 35 is transformed into parallel rays of radiation 45 exiting the output surface 39, to strike on a fast gate G.
  • Each lenslet 43 of the Shack-Hartmann device 35 emits radiation, which is received by corresponding cells or pixels disposed on a detector 53.
  • the output surface 39 of the Shack-Hartmann device 35 is supported on the sensing face 51 of the detector 53.
  • the Shack-Hartmann device 35 is shown distanced away from the detector 53, also for the sake of description.
  • the Shack-Hartmann device 35 and the detector 53 are implemented as a single-unit image intensifier.
  • the detector 53 is an image sensor, for example a CMOS, or a CCD, such as pertaining to a Basler camera model 102F, or another selected image sensor.
  • the eye 11, the first beam splitter 17, the first focusing lens 25, the spatial pinhole filter 29, the collecting lens 31, the Shack-Hartmann device 35, the fast gate G, and the detector 53 are all aligned along the main optical axis z.
  • the driver 21 acts to alternately block and unblock or alternately activate and deactivate the fast gate G.
  • the driver 21 is denominated modulator.
  • the fast gate G has an input surface 47 and an output surface 49.
  • the input surface 47 receives the parallel rays of radiation 45, which, according to the state of the gate G, are either blocked or allowed to propagate.
  • the driver 21 commands the gate G into an open state, passage is permitted and radiation exits via the output surface 49 onto the image sensor 53.
  • the CCD 53 detects and captures the signals and the information received from the Shack-Hartmann lenslets 35, via the gate G, These captured signals are forwarded to a processing unit 55, coupled to the CCD 53.
  • the processing unit 55 has a memory not shown in the Figs, and is configured to receive, store, read, and run signal, image processing, and application computer programs.
  • Such computer programs include for example wave front analysis, optical application programs, geometric processing and display programs, and surface reconstruction algorithms for the correction and enhancement of images.
  • the processing unit 55 After treatment by the processing unit 55, the derived results are displayed as processed images on a monitor 57, which is also coupled to the processing unit 55. If desired, raw or processed signals may be dispatched to further input and/or output equipment, not shown in Fig. 1 but also coupled to the processing unit 55, or to the monitor 57. In addition, still not shown in Fig. 1, input/output devices may be coupled to the processing unit 55 for use by the eye-care specialist.
  • monitor 57 is used to designate one or more display devices.
  • the processing unit 55 is further coupled in bi-directional communication with the driver 21 to receive data, such as modulation, and for management and control of the operation of the retina imager RI.
  • Fig. 3 illustrates an incoming flat wave front WF and an optical path directed along the positive z-axis, on which are disposed a focusing lens FL and a detector D.
  • the flat wave front WF progressing along the z-axis toward the focusing lens FL is incident in perpendicular thereto, and the detector D is disposed at the focal distance f behind the focusing lens FL, then the wave front WF beam impinges at the center O of the detector D.
  • the flat wave front WF is tilted to an angle ⁇ , say in the plane x-z, then the wave front WF beam deviates from the center O of the detector D and is focused thereon off-center, at a deviation distance ⁇ .
  • the off-center ⁇ , or deviation ⁇ on the surface of the detector D is approximated as
  • the local derivative of the wave front WF may be regarded as being equal to the focal deviation ⁇ divided by the focal length f.
  • each measurement received on a cell of the detector D for example at each pixel cell of a CCD, one may calculate two local derivatives, with respect to the axes x and y, and generate to matrices:
  • the surface of the wave front WF is approximated by help of an appropriately chosen set of functions.
  • the radiation 45 contains the reflection from the cornea CRN and from the lens LNS, the reflection from the retina R, and the aberrations incurred during the passage of the reflected light through the cornea CRN and the lens LNS, which also have to be accounted for. Only the net reflection from the retina R, which contains the required morphological information, is desired. The first reflection from, and the aberrations related to the cornea CRN and to the lens LNS, are both unwanted.
  • the deletion of the first reflection from the cornea CRN and from the lens LNS is achieved by controlled operation of the fast gate G in association with the driver 21.
  • the fast gate G is operated to "window", the pulses of reflections of light returned by the eye 11.
  • “Windowing” is a technique disclosed in US Patent No. 6, 057, 909 entitled “Optical ranging camera", which is incorporated herewith in whole by reference.
  • G. J. Iddan and G. Yahav describe a 3D Camera with a fast gate shutter in "3D Imaging in the Studio (and Elsewhere ...)", in “Three-Dimensional Image Capture and Applications", Proceedings of the SPIE Vol. 4298 (2001).
  • Fast gates G and fast gating are an optical technique developed by and proprietary of 3DV Systems Ltd. of Yokneam, Israel, and are briefly described.
  • Fast gates are known in the art as gated intensifiers, or liquid crystal shutters, or opto-electronic shutters, or electro-optical crystal shutters, and as solid-state optical or solid-state opto-electronic very high-speed shutters.
  • a "Solid State Optical Shutter” is described in US Patent No. 6,057,909, and a "Large Aperture Optical Image Shutter” is disclosed in US Patent No. 6,331,911, both being incorporated herewith in whole by reference.
  • a fast gate, or solid-state optical shutter is a generally planar substrate made of semiconductor material, having mutually substantially parallel input and output surfaces controllable by an electrical signal.
  • Fast gates may be switched rapidly between the open and the closed state, with typical very high-speed gate transition times of less than one nanosecond and even within tens of psec (picoseconds).
  • the source of radiation S provides generally uniform illumination of the retina R, and the driver 21 modulates the illumination.
  • the driver 21 is configured to control the triggering of say rectangular, trapezoidal, or other pulses of light, for a period of time having a duration TL, and mutually separated apart in time by ⁇ L.
  • diagram [a] depicts two sequential pulses of illumination light PL distributed along a time axis tl and having an intensity of 1 when the source of radiation S is turned on and illuminates, and an intensity of 0 when turned off.
  • Each pulse of illumination lasts for a duration of time TL of less than one nanosecond.
  • the time lapse mutually separating two consecutive pulses PL is ⁇ L.
  • each pulse of light PL causes two reflections, namely one from both the cornea CRN and the lens LNS, and one from the retina R.
  • Diagram [b] of Fig. 4 shows the reflections resulting from each one of the two shown pulses of light PL, in distribution along a time axis tr.
  • the first reflection, returned from the cornea CRN and from the lens LNS, is shown as curve bCL (Cornea and Lens), immediately followed by the second reflection from the retina R, indicated as curve bR.
  • the amplitude A of the cornea and lens reflection bCL is much higher than that of the relatively weak retinal reflection bR.
  • FIG. 4 Diagram [c] in Fig. 4 represents open and closed states of the gate G, along a time axis tg, shown as a couple of trapezoidal curves Gc, synchronized with the illumination pulses PL, and the resulting reflection pulse bR.
  • the curve Gc represents the gate G, which is open for the duration of time shown as TG.
  • the gate G is open when at amplitude 1, and closed at amplitude 0.
  • the driver 21 is configured to trigger illumination, and to keep the gate G closed, especially for the duration of the first reflection pulse bCL. Then, immediately after the passage of the first reflection pulse bCL, the gate G is opened with a very fast rise time of about 50 psec (picoseconds), to permit passage of the retinal reflection pulse bR. Typically, the gate remains open for as long as about one nanosecond, and does not require a fast decay time when closing. In other words, the driver 21 commands the fast opening rise of the curves Gc from the closed state 0 to the open state 1. Thereby, the first reflection pulse bCL is blocked and only the retina reflection pulse bR is permitted passage and propagation toward the detector 53. Diagram [d] of Fig.
  • FIG. 4 illustrates a pair of signals, shown as curves dD, collected by the detector 53, along the time axis td. Only signals of amplitude I, derived from the retina reflection pulses bR are detected, in synchronization with the operation of the gate G.
  • the waveforms in Fig. 4 are shaped as rectangular or trapezoidal pulses, other waveform shapes may also be used. It is understood that the pulse- shapes in Fig. 3 are idealized, for the sake of ease of description, but such ideal pulse-shapes are not necessary for the operation of the present invention.
  • the illumination flash pulse PL is fast rising and of short duration, and is repeated only after the gate G is closed.
  • the gate G must first be closed, meaning that the curve Gc must return to the state 0 before a next pulse of illumination PL is triggered.
  • the rise time of the gate G shown as curve Gc, is required to be very fast and last not more than 50 psec for the transition from the closed state 0 to the open state 1.
  • the signals shown as curves dD need now to be corrected to remove the aberrations suffered during passage through the cornea CRN and the lens LNS.
  • the measurement of the aberrations caused by the cornea CRN and the lens LNS are obtained by application of methods commonly used by ophthalmologists and optometrists.
  • the simplest way is to take advantage of the availability of the Shack-Hartmann device 35 operative with the RI, as conventionally used.
  • the Shack-Hartmann device 35 is operated under illumination from the source S, and the aberrations due to the cornea CRN and the lens LNS are measured, and fed into the processing unit 55.
  • computer application programs running on the processing unit 55 are operated to appropriately correct and subtract the unwanted aberrations from the collected signals, shown as curves dD. It is noted that illumination from the source S is either continuous or pulsed.
  • Wavefront aberration measurement is disclosed, as a sample out of the many inventions in that field, in the following US Patent Applications No. 2003/0053031 Al to Wirth, No. 2003/0058403 Al Lai et al., and No. 2003/0086063 Al to Williams et al.
  • the focusing lens 15 shown in Fig. 1 is focused on a point RF of the retina R, which is shown in Fig.5, and is disposed on the main optical axis z. Focusing is achieved by translation of the lens 15 in either one of both directions along the x-axis, as indicated by the double-headed arrow AA.
  • the incoming illumination wave front 19 is reflected from point RF to exit the eye 11 as an aberrated beam 25. Thereafter, the aberrated beam 25 progresses via the Shack- Hartmann device 35, until the detector 53 is reached, where the aberration is derived by conventionally known means.
  • the processing unit 55 now appropriately corrects the collected retinal signals shown as curves dD.
  • the duration of a standard video field is about 16 msec, while the durations of the pulses of illumination are typically less than one nanosecond, it will be appreciated that hundreds or thousands of such pulses may be included in the time of a single field or frame.
  • Such multiple-pulse modulation functions are useful in increasing the singnal/noise ratio of the image produced by the retinal imager RI.
  • the RI is thus configured to present an image of a layer of the retina R, according to the wavelength of the illumination source S.
  • Fig. 6 presents a preferred embodiment 200 of the RI, where the gate G is relocated relative to the configuration of embodiment 100.
  • the gate Gl is disposed adjacent the exit of radiation from the spatial pinhole filter 29.
  • the configuration of embodiment 200 permits to use a smaller gate Gl, relative to gate G shown in Fig. 1, since the aperture of the pinhole has a diameter of about 0.5 mm. It is well known that small gates are cheaper and respond faster than large- aperture gates.
  • Radiation proceeds from the gate Gl to the collecting lens 31, and from there, via the Shack-Hartmann device 35 and the image sensor 53, to the processing unit 55.
  • the principles of operation and the use of the embodiment 200 of the RI are the same as with the embodiment 100.
  • the retina R is a structure of living biological tissue.
  • the retina R has a number of sub-layers and membranes, with different functions in the generation of the retina's functionality as the image- generating organ of the body. It is the mapping of the layered structure and of the different layers of tissue that is of great value to eye-care specialists.
  • the RI as an apparatus for providing an image of various layers of the retina R, by way of real time wavelength discrimination, or color separation.
  • each wavelength say ⁇ l, ⁇ 2, ... ⁇ n
  • retina layers at different depths are penetrated.
  • blue, green, and red radiation are referred to hereinbelow, although implying the array of radiation ⁇ l, ⁇ 2, ... ⁇ n.
  • blue, green, and red radiation blue will reach but shallow depth, green will reach deeper, and red penetrates the deepest.
  • IR radiation is used for the illumination of the retina R.
  • a first advantage is that IR radiation penetrates deeper into biological tissue.
  • a second advantage is that high intensity IR illumination does not harm the eye 11.
  • the third advantage is that semi-conductor fast gates for IR radiation are easier to implement, and are therefore cheaper.
  • the gate Gl is supported in front of the spatial pinhole filter 29 if desired. Although this last alternative is not shown in the Figs., radiation passes first via the gate Gl, and next through the pinhole filter 29.
  • the driver 21 is coupled to the gate Gl, and the control configuration remains the same as for embodiment 100.
  • the principles of operation and the use of embodiment 200 of the RI are the same as with the embodiment 100.
  • a multi-wavelength illumination source S ⁇ n for illumination in different separate wavelengths.
  • three wavelength sources S ⁇ l, S ⁇ 2, and S ⁇ 3, may have a wavelength of, respectively, ⁇ l, ⁇ 2, and ⁇ 3, representing for example, blue, green, and red radiation.
  • the source S ⁇ n is not limited to any particular number of wavelengths, but is configured as desired. Other wavelength mixing methods are also possible.
  • Each source of illumination S ⁇ l, S ⁇ 2, and S ⁇ 3 emits a beam of radiation, respectively, 71, 72, and 73, directed to impinge on a wavelength collimating lens, respectively, 74, 75, and 76.
  • each collimating lens 74, 75, and 76 is directed toward a wavelength-reflecting semi-transparent mirror, respectively 77, 78, and 79.
  • Each mirror is configured to reflect the desired wavelength and to permit passage therethrough of other wavelengths.
  • the mirrors 77, 78, and 79 are aligned along the x-axis and are configured to direct respective radiation toward the lens 15, shown in the various Figs.
  • the processing unit 55 may produce a display on the monitor 57 shown in Fig. 1, of each wavelength S ⁇ l, S ⁇ 2, and S ⁇ 3 that is specific to one layer of the retina R, alone or in desired combination.
  • another preferred embodiment 300 of the RI is configured for simultaneous operation in three wavelengths.
  • a TIR prism 811 or Total Internal Reflection prism 811, is aligned on the main optical axis z, downstream of the output of the first beam splitter 17.
  • radiation impinging on the TIR prism 811 is deflected in three different and separate wavelength channels, with, say blue BL, green GR, and red RD radiation.
  • the radiation output surfaces of the TIR prism 811 are marked respectively as 811BL, 811GR, and 811RD.
  • Each wavelength is aligned as a separate wavelength channel along one optical axis: blue BL and green GR are deflected on both sides of the main axis z, along which red RD is disposed.
  • the three channels for blue, green, and red radiation are identical, except for the fast gates G ⁇ l, G ⁇ 2, and G ⁇ 3, each one being selected according to the respective radiation wavelength blue, green, and red.
  • each optical axis blue BL, green GR, and red RD are identical to embodiment 200, from the second focusing lens 27 to the detector 53.
  • the elements disposed along each optical axis carry the same designation numerals with the addition of a suffix according to the optical axis to which they pertain.
  • the processing unit 55, and the monitor 57 are preferably shared.
  • the detectors 53BL, 53GR, and 53RD are coupled to the same processing unit 55, and the monitor 57, even though separate processing units, respectively 55BL, 55GR, and 55RD, and separate monitors 57BL, 57GR, and 57RD, all last six not shown in the Figs., are possible if desired.
  • one single processor-operated driver 21 is coupled to one single source of radiation S, and to the common processing unit 55.
  • two connecting lines are omitted: the numeral 21 is indicated in associated with the source S and with the gate GG to indicate a link to the driver 21.
  • the principle of operation and the use of embodiment 300 of the RI remains the same as for embodiment 200. However, wavelength discrimination, or color separation, are accompanied by simultaneous real time derivation and processing.
  • the eye-care specialist may retrieve three different layers of the retina R, or more depending on the number of wavelength channels, and thus derive maps and morphologic imaging of different depth of the retina R, all for display in real time on the monitor 57.
  • Image processing programs running on the processing unit 55 allow display as desired, such as for example, presentation on the monitor 57, alone and in combination, of layers, isometric 3D views, and portions thereof.
  • Fig. 9 presents only a partial view of an embodiment 400 of the RI, to be added, if desired to any of the embodiments 100, 200, and 300 described hereinabove. By the addition of a color channel, the embodiment 400 permits to further enhance images presented to the eye-care specialist.
  • Fig. 9 presents only a partial view of an embodiment 400 of the RI, to be added, if desired to any of the embodiments 100, 200, and 300 described hereinabove.
  • a color-beam splitter 59 is aligned on the main optical axis z, downstream and adjacent the first beam splitter 17.
  • the color-beam splitter 59 directs the imprinted wavefront 25 toward both the second focusing lens 27, and an imaging lens 61.
  • a color imager 63 captures the radiation exiting from the imaging lens 61, to derive color images of the retina R.
  • the color-beam splitter 59, the imaging lens 61, and the color imager 63 are aligned along an x-axis x' parallel to the x-axis.
  • the color imager 63 displays the derived images either on the monitor 57 to which it is coupled, or on another separate monitor, not shown in Fig 9.
  • An eye- care specialist may now obtain monochrome images of different wavelengths in superimposition on color images of the retina R.
  • the eye 11 is illuminated by the source S, which is focused on the center 113 of the eyeball 111 to illuminate the retina R.
  • the RI is then operated to derive reflection from the retina R, in one or more illumination wavelength.
  • the lens 15 is translated to focus illumination on the retina R, at point RF, to derive eye- aberration measurements.
  • the retinal reflection is corrected by these last eye-aberration measurements and the processing unit 55 processes desired images.

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Abstract

Apparatus and method for providing a three-dimensional image of an ocular retina (R). A source of light (S) flashes illumination on the examined eye (11) wherefrom reflected light is returned. The reflected light carries a first reflection returned from the cornea (CRN) and from the lens (LNS) and a second reflection returned from the retina (R). A fast gate (G) remains closed to block the first reflection and is opened for passage of the second reflection onto a detector (53), via s Shack-Hartmann device (35). Data derived by the Shack-Hartmann device is forwarded to a processing unit (55) coupled to the detector. The Shack-Hartmann device is then used in the conventional way to provide eye aberrations measurements, which are used to correct the second reflection. After eye-aberration correction, the second reflection is the net reflection from the retina. Illumination at different wavelengths permits to map corresponding layers of the retina.

Description

METHOD AND APPARATUS FOR MAPPING A RETINA Technical Field The present invention relates in general to imaging of the eye, and in particular to the morphological three-dimensional imaging of the retina of the eye. Background Art
Nowadays, an eye-care specialist may take advantage of any of the three most prominent existing retinal diagnostic tools, which are the fundus camera, the Optical Coherence Tomograph, and the Heidelberg confocal microscope.
The fundus camera takes two-dimensional images only, and therefore lacks the three-dimensional imaging capability that is so important to an eye-care specialist for diagnostic purposes.
The Optical Coherence Tomograph is able to provide optical biopsy, which is a detailed description of the retina layer structure, similar to the information retrieved by classical microscope biopsy. However, the Optical Coherence Tomograph does not present a complete 3D-model and the equipment is rather onerous, thus affordable only to large medical facilities.
The Heidelberg confocal microscope uses scanning techniques to derive details of the retinal layers, which scanning procedures are inherently time consuming. Furthermore, the Heidelberg confocal microscope has the disadvantage of being an expensive device.
Prior art related to the internal ocular surface is referred to in the following disclosures. In US Patent No. 6, 810,140, Yang et al. disclose "a three dimensional real¬ time apparatus for imaging an ocular retina which comprises a laser generating device for generating laser beams, an optical means for making the output angles of imaginary or extended lines of the laser rays reflected from the retina agree with the incident angles of the same laser beams irradiated on the retina at respective moments in both the vertical and horizontal direction and a three dimensional imaging means for converting the image of the retina extracted from the optical means to a real-time three dimensional image." Yang et al. do not use single shot illumination of the field of view, and do not operate a Shack-Hartmann device in association with fast gating. US Patent No. 5,220,360, to Verdooner et al. disclose "An apparatus and method for topographically mapping an internal ocular surface, including projection means for projecting a plurality of parallel lines onto the internal ocular surface in a specified line orientation and with a specified direction of projection, camera means for capturing an image of the internal ocular surface having parallel lines projected thereon, the image being captured at an angle from the direction of projection, and means connected to the camera means for generating digital picture element data representative of the image of the internal ocular surface and for identifying the picture element locations of images of the parallel lines in the image and for generating a topographical map of said internal ocular surface based on imaged curvatures of the projected parallel lines, and comparison means associated with the computer means for retrieving at least one of the types of previously stored data relating to said internal ocular surface and then comparing a first topographical map generated from said previously stored data to a second topographical map generated from more recently obtained data relating to the same internal ocular surface, to identify differences in topography between said first and second maps, for, among other purposes, detecting diseases such as glaucoma." Verdooner et al. thus illuminates the retina by projecting perpendicular gridlines, and then calculates the topography from the received images, which is different from the present application. Verdooner et al. do not use single shot illumination of the field of view and do not operate a Shack-Hartmann device in association with fast gating.
International Publication WO03051187 to Polland relates to "ophthalmic wavefront and topography measurement and more particularly to devices and methods for improved wavefront measurement using a sequential scanning technique, and to an apparatus and method for making retinal topography measurements." Polland uses sequential scanning, does not use single shot illumination of the field of view, and does not operate a Shack-Hartmann device in association with fast gating. In US Patent Application No. 20030053029, Wirth describes "An ophthalmic instrument comprising: a wavefront sensing illumination source producing light that is formed as a spot image on the retina of the human eye and reflected there from; and a wavefront sensor that estimates aberrations in reflections of the light formed as a spot image on the retina of the human eye, wherein the wavefront sensor comprises a beam splitter operably disposed between a lenslet array and multiple imaging devices, said lenslet array forming a first array of spots, and said multiple imaging devices capturing multiple images of said first array of spots for use in estimating said aberrations." In contrast with the present invention, Wirth measures aberrations. It is also known that a company by the name of Talia, in Jerusalem, Israel, has developed a retinal thickness measurement instrument (RTA) based on structured light, but information regarding performances is not available. It is therefore still uncertain if the new tool will match the needs of the eye-care specialist community. Although related to the technical field, none of the citation hereinabove provides a real time image of the retina as a 3D mapping achieved by use of a Shack-Hartmann device in association with fast gating during a single shot illumination lasting 100 milliseconds. The prior art dealing with the imaging of the retina does not disclose a "one shot" area illumination of the whole field of view, and furthermore, does not use a gated Shack-Hartmann diagnostic apparatus for providing a three dimensional (3D) morphological image of the retina of an eye under examination, as with the present invention. It would thus be advantageous to provide the eye-care specialist community with a real time Retinal Imager, or RI, for topographically mapping an internal ocular surface, that is simple, low cost, fast operating and three-dimensional, affordable to small clinics and to practitioners for use in their offices. Such a retina imager (RI) has also to provide the eye-care specialist with the ability to gain diagnostic data concerning medical conditions such as glaucoma, diabetes, age- related disorders of the retina, as well as other diseases. Disclosure of the Invention
The problem consists of the need to provide the eye-care specialist community with a simple, low cost method and an apparatus for the real time imaging and 3D topographical mapping of an internal ocular surface.
The solution is provided by a method and an apparatus operating a source of light-flash illuminations on the examined eye wherefrom reflected light is returned. The reflected light carries a first reflection returned from the front portion of the eye, i.e. from the cornea and from the lens, and a second reflection returned from the retina.
It is the second reflection returned from the retina that contains the desired information. Therefore, the first reflection must be deleted, which is achieved by the help of a fast gate being disposed on the optical path of the reflection from the eye. The fast gate remains closed to block the first reflection and is opened for passage of the second reflection, which is directed onto a detector, via a Shack- Hartmann device. Data derived by the Shack-Hartmann device is forwarded the detector for data collection, and to a processing unit coupled to the detector. The Shack-Hartmann device is then operated separately in the conventional way to provide eye aberrations measurements, which are forwarded to the processing unit and are used to correct the second reflection. After eye-aberration correction, the second reflection is now the desired net reflection from the retina.
Illumination with different wavelengths permits to map corresponding layers of the retina. For example, simultaneous illumination in three different wavelengths will send radiation to penetrate into three different layers of the retinal tissue. A 3D morphology of the retina is thus obtained in real time.
Images derived by the processing unit are displayed on one or more monitors, in monochrome and in color, alone and in superposition, before or after further image processing.
It is an object of the present invention to provide a method and an apparatus for examining the retina of an eye. A source of illumination is directed onto the retina, creating reflections returned from the eye. A Shack-Hartmann device is used for receiving reflections returned from the eye, and for transmitting information derived from the received reflections. Furthermore, an image sensor is employed for capturing reflections received via the Shack-Hartmann device, and for emitting signals derived from the captured reflections. Moreover, a processing unit is coupled to the image sensor, for receiving data from the image sensor, and for processing and delivering processed data. For use, the source of illumination is triggered to emit at least one pulse of light as a flash lasting for a predetermined duration of time. In association, the fast gate is opened into a first open state and closed into a second closed state in predetermined synchronization with the at least one pulse of light, and the processing unit is operated to derive a retina map from the data received from the image sensor via the fast gate. It is another object of the present invention to provide a source of illumination configured to emit light such as invisible light, visible light, coherent light, white light, infrared light, and/or ultraviolet light.
It is yet an object of the present invention to provide a source of illumination configured to emit light in a plurality of different discrete wavelengths wherefrom a discrete wavelength out of the plurality of different discrete wavelengths is controllably selected. The source of illumination may be triggered to emit a sequence of pulses of light including at least one selected wavelength, or at least two different wavelengths, or more wavelengths.
It is still another object of the present invention to provide a source of illumination controllable to focus illumination on either one of both the retina and a selected location in the interior of the eye, with the duration of the at least one pulse of illumination light lasting for less than one nanosecond.
It is yet still an object of the present invention to provide a fast gate operated to open from the closed state into the open state within less than one nanosecond, and even within less than 100 picoseconds, but the gate must be operated to close from the open state into the closed state before a next pulse of light is emitted in succession to the at least one pulse of light.
It is one more object of the present invention to provide for the reflections returned from the eye to pass first via the gate and next via the Shack-Hartmann device, or vice versa, but to pass always via a spatial pinhole filter disposed to receive reflections returned from the eye prior to passage of the reflections via the gate and the Shack-Hartmann device, to prevent capture of stray rays of light.
It is an additional object of the present invention to provide a driver that is coupled to the gate and to the source of illumination for synchronization of mutual operation of the gate and of the source of illumination, for the driver to trigger the source of illumination to emit the at least one pulse of light in repetitive succession, and for the fast gate to be operated to open into an open state and to close into a closed state in predetermined synchronization with the at least one pulse of light.
It is yet an additional object of the present invention to provide a driver coupled to the gate and to the source of illumination, a processing unit coupled to the driver for control and management of retina mapping, and a monitor coupled to the processing unit for displaying data received from the image sensor as at least one image derived from the retina, with the gate and the source of illumination are selected to match in wavelength.
It is still an additional object of the present invention to provide a a method and an apparatus wherein each at least one pulse of light is limited to a duration short enough to ensure that a second reflection returned from the eye as a retinal reflection will reach the gate after termination of a first reflection returned from the eye as a first reflection from the cornea and from the lens, to permit time domain discrimination between the first reflection and the retinal reflection, where a driver is coupled to the gate and to the source of illumination for synchronization of mutual operation of the gate and of the source of illumination, and the driver controls the gate to remain in the closed state and to deny passage of each one first reflection pulse, and then controls the gate to open from the closed state into the open state and to permit passage of each one of the second reflection pulses being reflected from the retina, whereby the image sensor receives only second reflection pulses reflected from the retina. It is yet one more object of the present invention to provide the s Shack-
Hartmann device operated to derive aberration measurement of the cornea and of the lens of the eye under examination, and where the processing unit is configured to correct each one of the second reflection pulses for aberration due to the cornea and to the lens by help of the derived aberration measurement, whereby the processing unit which is coupled to a monitor provides net retina reflection data derived from the second reflection pulses which are corrected for eye aberration.
It is furthermore an object of the present invention to provide for the reflections reflected from the eye to be directed to pass through a pinhole of small dimension pertaining to a spatial pinhole filter having a first side and a second side, where the gate is supported on either one of both the first side and the second side of the pinhole filter to receive reflections, and where the gate is configured to match the small dimension of the pinhole, whereby a gate of small dimension is operable for mapping the retina. It is moreover an object of the present invention to provide for a portion of the reflections returned from the eye to be deflected toward a color imager, and for the color imager to be coupled to a color monitor for displaying color images of the retina, whereby a color image may be superimposed on a reconstructed 3D retinal morphology. It is one more additional object of the present invention to provide for a portion of the reflections returned from the eye to be deflected toward a color imager that is coupled to the processing unit and to a monitor, and for the processing unit to be operated for image processing and for derivation of a retina map from the data received via the image sensor, whereby the processing unit is operative for displaying monochrome images on the monitor and color images on the color imager, and to provide monochrome images alone and in superposition with color images on the color imager.
It is furthermore one more additional object of the present invention to provide for a total reflection prism to be disposed to receive and transmit reflections returned from the eye, and to be configured to deflect the received reflections into three separate channels, each channel out of the three channels being oriented in one direction different from the direction of the other two channels, and each channel carrying only one single wavelength different from the wavelength of the other two channels, each channel operating a separate aggregation of equipment aligned along the direction of the respective channel, the equipment including at least one of each a Shack-Hartmann device, a pinhole filter, a gate selected to match the wavelength of the respective channel, and an image sensor, a driver being coupled to each one gate out of the three channels and to the source of illumination for synchronization of mutual operation of the three gates and of the source of illumination, and for triggering the source of illumination to emit the at least one pulse of light in repetitive succession, and the processing unit being coupled to each one of the three image sensors and to a monitor, whereby images derived from the retina in real time in three different wavelengths are displayed alone and in superposition on the monitor as a 3D map of the retina corresponding to the three different wavelengths of the total reflection prism. Brief Description of the Drawings The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: Fig. 1 is a diagram of a first embodiment 100 of a retinal imager, Fig. 2a depicts an example of signals derived from a flat wave front, Fig. 2b shows an example of signals derived from a morphology imprinted wave front,
Fig. 3 illustrates the analysis of the an imprinted wave front, Fig. 4 depicts the synchronization of the windowing process, Fig. 5 illustrates focusing on the retina for calibration purposes. Fig. 6 is a diagram of a second embodiment 200 of a retinal imager,
Fig. 7 depicts an illumination source with multiple illumination wavelengths, Fig. 8 is a diagram of a third embodiment 300 of a retinal imager, and Fig. 9 is a diagram of a fourth embodiment 400 of a retinal imager. Best Modes for Carrying out the Invention The present invention is of a system and a method for providing a three dimensional (3D) morphological image of the retina of the eye.
The following patents assigned to the assignee of the present patent application, and pertaining to fast gating, optical ranging and windowing, are incorporate herewith in whole by reference: US Patents No. 6,057,909 entitled "Optical ranging camera"; 6,091,905 entitled "Telecentric 3D camera and method"; No. 6,100,517 entitled "Three dimensional camera"; No. 6,331,911 entitled "Large aperture optical image shutter"; and No. 6,483,094 entitled "Solid state optical shutter".
In broad lines, the Retinal Imager, or RI, measures, and later reconstructs, a wave front of light directed toward and then reflected by the retina. A high-speed shutter for fast gating is operated to "window" the reflected wavefront so as to extract only a wavefront imprinted with signals reflected from the retina.
Thereafter, a Shack-Hartmann lenslets array is operated to receive the imprinted wavefront and to transmit information derived therefrom to an imaging device, and a processing unit calculates results. The results, which are displayed on a monitor, are provided as a 3D morphological image of the retina of the eye under examination.
Fig. 1 illustrates a diagram of a first embodiment 100, of a Retinal Imager, or RI, for the 3D morphological imaging of the retina R of an eye 11 illuminated by a source of radiation S. A beam of light 13 emitted by the source S, a lens 15, and a first beam splitter 17 are all oriented along an optical axis co-linear with an x-axis of Cartesian coordinates. The lens 15 is disposed for translation in both directions along the x-axis, as shown by the double-headed arrow AA5 to permit focusing of radiation as desired. The beam of light is of any desired visible or invisible wavelength of light, but is preferably infrared (IR) radiation. Possible sources of light are laser light, provided by Laser Diodes (LD), Laser Emitting Diodes (LED), or laser light provided by optical fibers. Typically, the emitted beam is a train of successive flashes of light, each flash lasting for less than one nanosecond.
The source of radiation S is coupled to and controlled by a processor-operated driver 21, operating as a source modulator for modulating the source of radiation S. Preferably, the driver 21 modulates the radiation to alternately block and unblock or alternately activate and deactivate the beam of light 13. The driver 21 is referred to as a modulator in the incorporated patents referred to hereinabove.
The driver 21 has a trigger, not shown in the Figs, for the sake of simplicity, for triggering the source of radiation S to deliver the beam of radiation 13. The beam 13 is directed to pass through the lens 15, to create an illuminating wave front 19 propagating parallel waves. The wave front 19 reaches the first beam splitter 17, taken as the origin O of the system of Cartesian coordinates, from where it is deflected in perpendicular to the x-axis, and oriented along a main optical axis, which is the z-axis. The incoming deflected wave front 23 is now directed to impinge on the eye 11 under examination. When directed to impinge on the eye 11, along the negative portion of the z- axis, the incoming wave front 23 first crosses the cornea CRN and then the lens LNS, which focuses the beam of radiation on the center 113 of the eyeball 111, thus in the vitreous body VB, to illuminate the retina R. It is noted that the lens 15 is configured for translation in both directions along the x-axis, as indicated by the double-headed arrow AA. Translation of the lens 15 permits to focus the incoming wave front 23 as desired in the interior of the vitreous body VB, when desired, also on the retina R itself as indicated by RF in Fig. 1.
From the retina R, light is reflected along the main optical axis z, straight through the beam splitter 17, as a wavefront 25, imprinted with the morphology of the retina, i.e., carrying data representative of the form and of the structure of the retina R.
It is noted that the incoming wavefront 23 is also reflected by the cornea CRN and by the lens LNS. Furthermore, when the imprinted wavefront 25 exits the eye 11, aberrations due to passage via the cornea CRN and the lens LNS are added to the reflected radiation.
The imprinted wave front 25 is reflected in a direction opposite to the incoming impinging radiation, and crosses a second focusing lens 27, which is focused on a spatial pinhole filter 29, for eliminating stray light beams. Typically, the pinhole of the spatial pinhole filter 29 has a diameter of 0.5 mm. From the pinhole 29, radiation is collimated as a parallel beam 33, via a collecting lens 31, toward a Shack-Hartmann device 35.
The Shack-Hartmann device 35, well known in the art, has an input surface 37 covered with an array of lenslets 41, an output surface 39, and is commonly used for measuring optical aberrations of the eye. With the present invention, the Shack-Hartmann 35 device is operated both as a tool for mapping the topography of the surface of the retina R and in the conventional manner for the measurement of the optical aberrations of the eye. It is noted that the operation of the Shack- Hartmann device 35 is independent of the wavelength of the light used therewith, but is solely dependent of the properties of propagation of light.
Reference to the measuring principles of the Shack-Hartmann device regarding wavefront analysis is found in the publication entitled: "A Shack- Hartmann-Sensor based Aberrometer for Ophthalmic Diagnostics", by F. Weidner, and E. Schroder, proceedings of the SPIE Vol. 4434 (2001). The imprinted parallel wavefront 33 incident on the input surface 37 of the
Shack-Hartmann lenslets array 35 is transformed into parallel rays of radiation 45 exiting the output surface 39, to strike on a fast gate G. Each lenslet 43 of the Shack-Hartmann device 35 emits radiation, which is received by corresponding cells or pixels disposed on a detector 53. The output surface 39 of the Shack-Hartmann device 35 is supported on the sensing face 51 of the detector 53. In Fig. 1 the Shack-Hartmann device 35 is shown distanced away from the detector 53, also for the sake of description. In practice the Shack-Hartmann device 35 and the detector 53 are implemented as a single-unit image intensifier. The detector 53 is an image sensor, for example a CMOS, or a CCD, such as pertaining to a Basler camera model 102F, or another selected image sensor.
It is noted that the eye 11, the first beam splitter 17, the first focusing lens 25, the spatial pinhole filter 29, the collecting lens 31, the Shack-Hartmann device 35, the fast gate G, and the detector 53 are all aligned along the main optical axis z. Furthermore, the driver 21, which is also coupled to the gate G, modulates and synchronizes both the gate G and the source of radiation S. Preferably, the driver 21 acts to alternately block and unblock or alternately activate and deactivate the fast gate G. In the incorporated patents referred to hereinabove, the driver 21 is denominated modulator. As shown in Fig. 1, the fast gate G has an input surface 47 and an output surface 49. The input surface 47 receives the parallel rays of radiation 45, which, according to the state of the gate G, are either blocked or allowed to propagate. When the driver 21 commands the gate G into an open state, passage is permitted and radiation exits via the output surface 49 onto the image sensor 53. The CCD 53 detects and captures the signals and the information received from the Shack-Hartmann lenslets 35, via the gate G, These captured signals are forwarded to a processing unit 55, coupled to the CCD 53. The processing unit 55 has a memory not shown in the Figs, and is configured to receive, store, read, and run signal, image processing, and application computer programs. Such computer programs include for example wave front analysis, optical application programs, geometric processing and display programs, and surface reconstruction algorithms for the correction and enhancement of images.
After treatment by the processing unit 55, the derived results are displayed as processed images on a monitor 57, which is also coupled to the processing unit 55. If desired, raw or processed signals may be dispatched to further input and/or output equipment, not shown in Fig. 1 but also coupled to the processing unit 55, or to the monitor 57. In addition, still not shown in Fig. 1, input/output devices may be coupled to the processing unit 55 for use by the eye-care specialist. The term monitor 57 is used to designate one or more display devices.
The processing unit 55 is further coupled in bi-directional communication with the driver 21 to receive data, such as modulation, and for management and control of the operation of the retina imager RI.
In principle, when a perfectly flat wavefront of light is incident on the input surface of a Shack-Hartmann lenslets array, parallel rays of light are transmitted to impinge on a detector. For the ease of description, it is assumed that the Shack- Hartmann device has only 16 lenslets. The output of the Shack-Hartmann device is received by the detector, which in turn outputs a perfectly aligned matrix showing 16 dots indicated as 211 in Fig. 2a, for example P(x, y). In the present illustrative example, each dot 211 of the aligned rows and columns of the matrix of dots corresponds to the output of one lenslet.
However, when an imprinted wave front is incident on the Shack-Hartmann device, the output thereof is not parallel-aligned rays of light. Each ray of light emitted by each lenslet is responsive to the received optical information carried by the imprinted wavefront. The output thereof on the detector is now a group of imprint- influenced dots 213, as shown in Fig. 2b, and not anymore a perfectly aligned matrix of dots 211. Wavefront deformations, such as with an imprinted wavefront, are proportional to the displacement of an imprint-influenced dot 213, for example P* (x+ Δx; y+ Δy) relative to a respective dot 211 with P (x; y). The deviations of the signals received on the detector, in Δx and in Δy, not shown in the Figs., permit to calculate and reconstruct the surface of the imprinted wave front. The approach taken for calculation of the deflections is described hereinbelow as an example only. The procedure used for the analysis of the wave front as performed by the processing unit 55 is now described by way of example, in relation with the set of perpendicular Cartesian coordinates shown in Fig. 3. See Davis, PJ.,
"Interpolation and Approximation", Chapter No. VIII, pp. 158-200, Dover Publications, Inc., New York, USA, 1975.
Fig. 3 illustrates an incoming flat wave front WF and an optical path directed along the positive z-axis, on which are disposed a focusing lens FL and a detector D. When the flat wave front WF progressing along the z-axis toward the focusing lens FL is incident in perpendicular thereto, and the detector D is disposed at the focal distance f behind the focusing lens FL, then the wave front WF beam impinges at the center O of the detector D. However, when the flat wave front WF is tilted to an angle α, say in the plane x-z, then the wave front WF beam deviates from the center O of the detector D and is focused thereon off-center, at a deviation distance ξ. For a tilt caused by a small angle α, the off-center ξ, or deviation ξ on the surface of the detector D is approximated as
Δz/Δx s ξ/f (1)
This means that the local derivative of the wave front WF may be regarded as being equal to the focal deviation ξ divided by the focal length f.
Therefore, from each measurement received on a cell of the detector D, for example at each pixel cell of a CCD, one may calculate two local derivatives, with respect to the axes x and y, and generate to matrices:
Ax = [(Δz/Δx)i, j] and Ay = [(Δz/Δy)i, j] (2), (3)
where i and j are indices.
By help of the data calculated for each one of the cells of the detector D, the surface of the wave front WF is approximated by help of an appropriately chosen set of functions. The most common set of functions are the Zernike polynomials, use of which yields: n z (x,y) = ∑ ak.zk (x, y) (4)
1 The series of coefficients ak are calculated by help of least squares approximation, as is common and well known in the art of applied mathematics. See for example Schwiegerling, Jim, "Field Guide to Visual Ophtalmic Optics", SPIE Press, Bellingham, Washington, USA, 2004. Still with reference to Fig. 1, it is from the information contained in the parallel rays of radiation 45 exiting the output surface 39 of Shack-Hartmann device 35 that the morphology of the retina R will be derived. As is, the parallel rays of radiation 45 contain three different types of information, all gathered during the propagation of light into and out of the eye 11. The radiation 45 contains the reflection from the cornea CRN and from the lens LNS, the reflection from the retina R, and the aberrations incurred during the passage of the reflected light through the cornea CRN and the lens LNS, which also have to be accounted for. Only the net reflection from the retina R, which contains the required morphological information, is desired. The first reflection from, and the aberrations related to the cornea CRN and to the lens LNS, are both unwanted.
To delete the first reflection from the cornea CRN and from the lens LNS, use is made of windowing and fast gating. In addition, calibration is conducted to filter out the aberrations by substraction. The order of these last two operations is irrelevant.
The deletion of the first reflection from the cornea CRN and from the lens LNS is achieved by controlled operation of the fast gate G in association with the driver 21. The fast gate G is operated to "window", the pulses of reflections of light returned by the eye 11. "Windowing" is a technique disclosed in US Patent No. 6, 057, 909 entitled "Optical ranging camera", which is incorporated herewith in whole by reference. Furthermore, G. J. Iddan and G. Yahav describe a 3D Camera with a fast gate shutter in "3D Imaging in the Studio (and Elsewhere ...)", in "Three-Dimensional Image Capture and Applications", Proceedings of the SPIE Vol. 4298 (2001).
Fast gates G and fast gating are an optical technique developed by and proprietary of 3DV Systems Ltd. of Yokneam, Israel, and are briefly described. Fast gates are known in the art as gated intensifiers, or liquid crystal shutters, or opto-electronic shutters, or electro-optical crystal shutters, and as solid-state optical or solid-state opto-electronic very high-speed shutters. A "Solid State Optical Shutter" is described in US Patent No. 6,057,909, and a "Large Aperture Optical Image Shutter" is disclosed in US Patent No. 6,331,911, both being incorporated herewith in whole by reference. A fast gate, or solid-state optical shutter is a generally planar substrate made of semiconductor material, having mutually substantially parallel input and output surfaces controllable by an electrical signal. Fast gates may be switched rapidly between the open and the closed state, with typical very high-speed gate transition times of less than one nanosecond and even within tens of psec (picoseconds).
As by Fig. 1, the source of radiation S provides generally uniform illumination of the retina R, and the driver 21 modulates the illumination. The driver 21 is configured to control the triggering of say rectangular, trapezoidal, or other pulses of light, for a period of time having a duration TL, and mutually separated apart in time by τL.
In Fig. 4, diagram [a] depicts two sequential pulses of illumination light PL distributed along a time axis tl and having an intensity of 1 when the source of radiation S is turned on and illuminates, and an intensity of 0 when turned off. Each pulse of illumination lasts for a duration of time TL of less than one nanosecond. The time lapse mutually separating two consecutive pulses PL is τL. When oriented toward the eye 11, each pulse of light PL causes two reflections, namely one from both the cornea CRN and the lens LNS, and one from the retina R.
Diagram [b] of Fig. 4 shows the reflections resulting from each one of the two shown pulses of light PL, in distribution along a time axis tr. The first reflection, returned from the cornea CRN and from the lens LNS, is shown as curve bCL (Cornea and Lens), immediately followed by the second reflection from the retina R, indicated as curve bR. The amplitude A of the cornea and lens reflection bCL is much higher than that of the relatively weak retinal reflection bR.
"Windowing" is now applied to "gate out" the first reflection pulse bCL. Diagram [c] in Fig. 4 represents open and closed states of the gate G, along a time axis tg, shown as a couple of trapezoidal curves Gc, synchronized with the illumination pulses PL, and the resulting reflection pulse bR. The curve Gc represents the gate G, which is open for the duration of time shown as TG. The gate G is open when at amplitude 1, and closed at amplitude 0.
The driver 21 is configured to trigger illumination, and to keep the gate G closed, especially for the duration of the first reflection pulse bCL. Then, immediately after the passage of the first reflection pulse bCL, the gate G is opened with a very fast rise time of about 50 psec (picoseconds), to permit passage of the retinal reflection pulse bR. Typically, the gate remains open for as long as about one nanosecond, and does not require a fast decay time when closing. In other words, the driver 21 commands the fast opening rise of the curves Gc from the closed state 0 to the open state 1. Thereby, the first reflection pulse bCL is blocked and only the retina reflection pulse bR is permitted passage and propagation toward the detector 53. Diagram [d] of Fig. 4 illustrates a pair of signals, shown as curves dD, collected by the detector 53, along the time axis td. Only signals of amplitude I, derived from the retina reflection pulses bR are detected, in synchronization with the operation of the gate G. Although the waveforms in Fig. 4 are shaped as rectangular or trapezoidal pulses, other waveform shapes may also be used. It is understood that the pulse- shapes in Fig. 3 are idealized, for the sake of ease of description, but such ideal pulse-shapes are not necessary for the operation of the present invention.
It is noted that the illumination flash pulse PL is fast rising and of short duration, and is repeated only after the gate G is closed. Thus, the gate G must first be closed, meaning that the curve Gc must return to the state 0 before a next pulse of illumination PL is triggered. Most important, since the physical distance separating the cornea CRN and the lens LNS from the retina R is about 20 mm, it is now understood why the rise time of the gate G, shown as curve Gc, is required to be very fast and last not more than 50 psec for the transition from the closed state 0 to the open state 1.
The signals shown as curves dD need now to be corrected to remove the aberrations suffered during passage through the cornea CRN and the lens LNS. The measurement of the aberrations caused by the cornea CRN and the lens LNS are obtained by application of methods commonly used by ophthalmologists and optometrists. The simplest way is to take advantage of the availability of the Shack-Hartmann device 35 operative with the RI, as conventionally used.
To this end, the Shack-Hartmann device 35 is operated under illumination from the source S, and the aberrations due to the cornea CRN and the lens LNS are measured, and fed into the processing unit 55. In turn, computer application programs running on the processing unit 55 are operated to appropriately correct and subtract the unwanted aberrations from the collected signals, shown as curves dD. It is noted that illumination from the source S is either continuous or pulsed.
Wavefront aberration measurement is disclosed, as a sample out of the many inventions in that field, in the following US Patent Applications No. 2003/0053031 Al to Wirth, No. 2003/0058403 Al Lai et al., and No. 2003/0086063 Al to Williams et al.
In practice, the focusing lens 15 shown in Fig. 1 is focused on a point RF of the retina R, which is shown in Fig.5, and is disposed on the main optical axis z. Focusing is achieved by translation of the lens 15 in either one of both directions along the x-axis, as indicated by the double-headed arrow AA. The incoming illumination wave front 19 is reflected from point RF to exit the eye 11 as an aberrated beam 25. Thereafter, the aberrated beam 25 progresses via the Shack- Hartmann device 35, until the detector 53 is reached, where the aberration is derived by conventionally known means. The processing unit 55 now appropriately corrects the collected retinal signals shown as curves dD.
Considering that the duration of a standard video field is about 16 msec, while the durations of the pulses of illumination are typically less than one nanosecond, it will be appreciated that hundreds or thousands of such pulses may be included in the time of a single field or frame. Such multiple-pulse modulation functions are useful in increasing the singnal/noise ratio of the image produced by the retinal imager RI.
The RI is thus configured to present an image of a layer of the retina R, according to the wavelength of the illumination source S.
Fig. 6 presents a preferred embodiment 200 of the RI, where the gate G is relocated relative to the configuration of embodiment 100. In Fig. 6 the gate Gl is disposed adjacent the exit of radiation from the spatial pinhole filter 29. The configuration of embodiment 200 permits to use a smaller gate Gl, relative to gate G shown in Fig. 1, since the aperture of the pinhole has a diameter of about 0.5 mm. It is well known that small gates are cheaper and respond faster than large- aperture gates.
Radiation proceeds from the gate Gl to the collecting lens 31, and from there, via the Shack-Hartmann device 35 and the image sensor 53, to the processing unit 55. The principles of operation and the use of the embodiment 200 of the RI are the same as with the embodiment 100.
Consideration is now given to the fact that the retina R is a structure of living biological tissue. The retina R has a number of sub-layers and membranes, with different functions in the generation of the retina's functionality as the image- generating organ of the body. It is the mapping of the layered structure and of the different layers of tissue that is of great value to eye-care specialists.
Hence, when the hereinabove-described monochromatic retina imaging procedure is repeated successively with light of appropriately selected wavelengths, it is possible to derive an image of each layer of the retina R. Therefore, it is advantageous to configure the RI as an apparatus for providing an image of various layers of the retina R, by way of real time wavelength discrimination, or color separation.
It is well known that when radiation of different wavelength λi impinges on biological tissue, each wavelength, say λl, λ2, ... λn, penetrates to a different depth. Therefore, when the retina R is illuminated with different wavelengths λi, retina layers at different depths are penetrated. For ease of description, blue, green, and red radiation are referred to hereinbelow, although implying the array of radiation λl, λ2, ... λn. For example, with blue, green, and red radiation, blue will reach but shallow depth, green will reach deeper, and red penetrates the deepest. Preferably, IR radiation is used for the illumination of the retina R. A first advantage is that IR radiation penetrates deeper into biological tissue. A second advantage is that high intensity IR illumination does not harm the eye 11. Finally, the third advantage is that semi-conductor fast gates for IR radiation are easier to implement, and are therefore cheaper.
In Fig. 6, the gate Gl disposed behind the spatial pinhole filter 29, thus downstream from the eye 11, is coupled to the driver 21, and the control configuration remains the same as for embodiment 100.
As an alternative, the gate Gl is supported in front of the spatial pinhole filter 29 if desired. Although this last alternative is not shown in the Figs., radiation passes first via the gate Gl, and next through the pinhole filter 29.
In both cases, independently of the gate Gl being coupled either in front of, or behind and downstream of the pinhole filter 29, the driver 21 is coupled to the gate Gl, and the control configuration remains the same as for embodiment 100. Evidently, the principles of operation and the use of embodiment 200 of the RI are the same as with the embodiment 100.
In Fig. 7 there is shown a multi-wavelength illumination source Sλn, for illumination in different separate wavelengths. For Sλn with n = 3, three wavelength sources Sλl, Sλ2, and Sλ3, may have a wavelength of, respectively, λl, λ2, and λ3, representing for example, blue, green, and red radiation. The source Sλn is not limited to any particular number of wavelengths, but is configured as desired. Other wavelength mixing methods are also possible.
For the ease of description, reference is made hereinbelow to blue, green, and red radiation, but multi-wavelength radiation is implied. Each source of illumination Sλl, Sλ2, and Sλ3 emits a beam of radiation, respectively, 71, 72, and 73, directed to impinge on a wavelength collimating lens, respectively, 74, 75, and 76. In turn, each collimating lens 74, 75, and 76, is directed toward a wavelength-reflecting semi-transparent mirror, respectively 77, 78, and 79. Each mirror is configured to reflect the desired wavelength and to permit passage therethrough of other wavelengths. AU the mirrors 77, 78, and 79 are aligned along the x-axis and are configured to direct respective radiation toward the lens 15, shown in the various Figs.
When the source of illumination Sλn is used with the embodiment 200 of the RI, in replacement of source S, it is possible to illuminate the retina R in various wavelengths. For example, the retina R may be illuminated separately and successively in three colors, thereby providing data regarding three different layers of the retina R. The processing unit 55 may produce a display on the monitor 57 shown in Fig. 1, of each wavelength Sλl, Sλ2, and Sλ3 that is specific to one layer of the retina R, alone or in desired combination. In Fig. 8, another preferred embodiment 300 of the RI is configured for simultaneous operation in three wavelengths.
In Fig. 8, a TIR prism 811, or Total Internal Reflection prism 811, is aligned on the main optical axis z, downstream of the output of the first beam splitter 17. Thereby, radiation impinging on the TIR prism 811 is deflected in three different and separate wavelength channels, with, say blue BL, green GR, and red RD radiation. The radiation output surfaces of the TIR prism 811 are marked respectively as 811BL, 811GR, and 811RD. Each wavelength is aligned as a separate wavelength channel along one optical axis: blue BL and green GR are deflected on both sides of the main axis z, along which red RD is disposed.
The three channels for blue, green, and red radiation are identical, except for the fast gates Gλl, Gλ2, and Gλ3, each one being selected according to the respective radiation wavelength blue, green, and red.
Downstream of the TIR prism 811, the elements on each optical axis blue BL, green GR, and red RD are identical to embodiment 200, from the second focusing lens 27 to the detector 53. The elements disposed along each optical axis carry the same designation numerals with the addition of a suffix according to the optical axis to which they pertain.
Downstream of the detectors 53BL, 53GR, and 53RD, the processing unit 55, and the monitor 57 are preferably shared. In other words, the detectors 53BL, 53GR, and 53RD, are coupled to the same processing unit 55, and the monitor 57, even though separate processing units, respectively 55BL, 55GR, and 55RD, and separate monitors 57BL, 57GR, and 57RD, all last six not shown in the Figs., are possible if desired. For control, one single processor-operated driver 21 is coupled to one single source of radiation S, and to the common processing unit 55. In Fig. 8, for the sake of clarity, two connecting lines are omitted: the numeral 21 is indicated in associated with the source S and with the gate GG to indicate a link to the driver 21. The principle of operation and the use of embodiment 300 of the RI remains the same as for embodiment 200. However, wavelength discrimination, or color separation, are accompanied by simultaneous real time derivation and processing.
In operation, the eye-care specialist may retrieve three different layers of the retina R, or more depending on the number of wavelength channels, and thus derive maps and morphologic imaging of different depth of the retina R, all for display in real time on the monitor 57. Image processing programs running on the processing unit 55 allow display as desired, such as for example, presentation on the monitor 57, alone and in combination, of layers, isometric 3D views, and portions thereof. Fig. 9 presents only a partial view of an embodiment 400 of the RI, to be added, if desired to any of the embodiments 100, 200, and 300 described hereinabove. By the addition of a color channel, the embodiment 400 permits to further enhance images presented to the eye-care specialist. In Fig. 9, a color-beam splitter 59 is aligned on the main optical axis z, downstream and adjacent the first beam splitter 17. The color-beam splitter 59 directs the imprinted wavefront 25 toward both the second focusing lens 27, and an imaging lens 61. A color imager 63 captures the radiation exiting from the imaging lens 61, to derive color images of the retina R. The color-beam splitter 59, the imaging lens 61, and the color imager 63 are aligned along an x-axis x' parallel to the x-axis.
The color imager 63 displays the derived images either on the monitor 57 to which it is coupled, or on another separate monitor, not shown in Fig 9. An eye- care specialist may now obtain monochrome images of different wavelengths in superimposition on color images of the retina R.
In use, the eye 11 is illuminated by the source S, which is focused on the center 113 of the eyeball 111 to illuminate the retina R. The RI is then operated to derive reflection from the retina R, in one or more illumination wavelength. Next, the lens 15 is translated to focus illumination on the retina R, at point RF, to derive eye- aberration measurements. The retinal reflection is corrected by these last eye-aberration measurements and the processing unit 55 processes desired images.
Industrial applicability is similar to that of other tools used by eye-care specialists. It will be appreciated by persons skilled in the art, that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention is defined by the appended claims and includes both combinations and subcombinations of the various features described hereinabove as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description.

Claims

1. A method for mapping a retina (R) of an eye (11) under examination, comprising: a source of illumination (S, Sλn) directed onto the retina and creating reflections returned from the eye, a Shack-Hartmann device (35) for receiving reflections returned from the eye, and for transmitting information derived from the received reflections, an image sensor (53) for capturing reflections received via the Shack- Hartmann device, and for emitting signals derived from the captured reflections, a processing unit (55) coupled to and for receiving data from the image sensor, and for processing and delivering processed data, the method being characterized by the steps of: triggering the source of illumination to emit at least one pulse of light as a flash lasting for a predetermined duration of time, operating a fast gate (G, Gl, GB, GG, GR) to open into a first open state and to close into a second closed state in predetermined synchronization with the at least one pulse of light, and operating the processing unit to derive a retina map from the data received from the image sensor via the fast gate.
2. The method according to Claim 1, wherein: the source of illumination is configured to emit invisible light.
3. The method according to Claim 1, wherein: the source of illumination is configured to emit visible light.
4. The method according to Claim 1, wherein: the source of illumination is configured to emit coherent light.
5. The method according to Claim 1, wherein: the source of illumination is configured to emit white light.
6. The method according to Claim 1, wherein: the source of illumination is configured to emit infrared light.
7. The method according to Claim 1, wherein: the source of illumination (Sλn) is configured to emit light in a plurality of different discrete wavelengths (Sλl, Sλ2, ..., Sλn) and a discrete wavelength out of the plurality of different discrete wavelengths is controllably selected, whereby the source of illumination is triggered to emit at least one pulse of light in at least one a selected wavelength.
8. The method according to Claim 1, wherein: the source of illumination (Sλn) is configured to emit light in a plurality of different discrete wavelengths (Sλl, Sλ2, ..., Sλn) and a discrete wavelength out of the plurality of different discrete wavelengths is controllably selected, whereby the source of illumination is triggered to emit a sequence of pulses of light including at least two different wavelengths.
9. The method according to Claim 1, wherein: the source of illumination is controllable to focus illumination on either one of both the retina and a selected location in the interior of the eye such as the eye center.
10. The method according to Claim 1, wherein: the duration of the at least one pulse of light lasts for less than one nanosecond.
11. The method according to Claim 1 , wherein: the fast gate is operated to open from the closed state into the open state within less than one nanosecond.
12. The method according to Claim 1, wherein: the fast gate is operated to open from the closed state into the open state within less than 100 picoseconds.
13. The method according to Claim 1, wherein: the fast gate is switched from the open state into the closed state before a next pulse of light is emitted in succession to the at least one pulse of light.
14. The method according to Claim 1, wherein: reflections returned from the eye pass first via the gate and next via the
Shack-Hartmann device.
15. The method according to Claim 1, wherein: reflections returned from the eye pass first via the Shack-Hartmann device and next via the gate.
16. The method according to Claim 1, wherein: a spatial pinhole filter (29) is disposed to receive reflections returned from the eye prior to passage of the reflections via the gate and the Shack-Hartmann device, to prevent capture of stray rays of light.
17. The method according to Claim 1, wherein: a driver is coupled to the gate and to the source of illumination for synchronization of mutual operation of the gate and of the source of illumination, and the driver triggers the source of illumination to emit the at least one pulse of light in repetitive succession.
18. The method according to Claim 1, wherein: a driver is coupled to the gate and to the source of illumination for synchronization of mutual operation of the gate and of the source of illumination, the driver triggers the source of illumination to emit the at least one pulse of light in repetitive succession, and the fast gate is operated into an open state and into a closed state in predetermined synchronization with the at least one pulse of light.
19. The method according to Claim 1, wherein: a driver is coupled to the gate and to the source of illumination for synchronization of mutual operation of the gate and of the source of illumination , and the processing unit is coupled to the driver for control and management of retina mapping.
20. The method according to Claim 1, wherein: a monitor is coupled to the processing unit for displaying data received from the image sensor as at least one image derived from the retina.
21. The method according to Claim 1, wherein: the gate and the source of illumination are selected to match in wavelength.
22. The method according to Claim 1, wherein: each at least one pulse of light is limited to a duration short enough to ensure that a second reflection returned from the eye as a retinal reflection will reach the gate after termination of a first reflection returned from the eye as a first reflection from the cornea and from the lens, to permit time domain discrimination between the first reflection and the retinal reflection, a driver is coupled to the gate and to the source of illumination for synchronization of mutual operation of the gate and of the source of illumination, and the driver controls the gate to remain in the closed state and to deny passage of each one first reflection pulse, and then controls the gate to open from the closed state into the open state and to permit passage of each one of the second reflection pulse being reflected from the retina, whereby the image sensor receives only second reflection pulses reflected from the retina.
23. The method according to Claim 22, wherein: the Shack-Hartmann device is operated to derive aberration measurement of the cornea and of the lens of the eye under examination, and the processing unit is configured to correct each one of the retinal reflections for aberration due to the cornea and to the lens by help of the derived aberration measurement, whereby the processing unit which is coupled to a monitor provides net retina reflection data derived from the second reflection pulses which are corrected for eye aberration.
24. The method according to Claim 1, wherein: reflections reflected from the eye are directed to pass through a pinhole of small dimension pertaining to a spatial pinhole filter having a first side and a second side, and the gate is supported on either one of both the first side and the second side of the pinhole filter to receive reflections, and the gate is configured to match the small dimension of the pinhole, whereby a gate of small dimension is operable for mapping the retina.
25. The method according to Claim 1, wherein: a portion of the reflections returned from the eye are deflected toward a color imager (63), and the color imager is coupled to a color monitor for displaying color images of the retina, whereby a color image may be superimposed on a reconstructed 3D retinal morphology.
26. The method according to Claim 1, wherein: a portion of the reflections returned from the eye are deflected toward a color imager which is coupled to the processing unit and to a monitor, and the processing unit is operated for image processing and for derivation of a retina map from the data received via the image sensor, whereby the processing unit is operative for displaying monochrome images on the monitor and color images on the color imager, and to provide monochrome images alone and in superposition with color images on the color imager.
27. The method according to Claim 1, wherein: a total reflection prism is disposed to receive and transmit reflections returned from the eye, and is configured to deflect the received reflections into three separate channels, each channel out of the three channels is oriented in one direction different from the direction of the other two channels, and each channel carries only one single wavelength different from the wavelength of the other two channels, each channel operates a separate aggregation of equipment aligned along the direction of the respective channel, the equipment including one Shack-Hartmann device, one pinhole filter, one gate selected to match the wavelength of the respective channel, and one image sensor, a driver is coupled to each one gate out of the three channels and to the source of illumination for synchronization of mutual operation of the three gates and of the source of illumination, and for triggering the source of illumination to emit the at least one pulse of light in repetitive succession, and the processing unit IS being coupled to each one of the three image sensors and to a monitor,
5 whereby images derived from the retina in real time in three different wavelengths are displayed alone and in superposition on the monitor as a 3D map of the retina corresponding to the three different wavelengths of the total reflection prism.
28. Apparatus (100, 200, 300, 400) for examining an eye (11) and operating in association with a fast gate (G, Gl, GB, GG, GR), comprising: o a Shack-Hartmann device (35) for receiving reflections returned from the eye and for transmitting information derived from the received reflections, a source of illumination (S, Sλn) directed onto an ocular retina (R) and creating reflections returned from the eye to reach the Shack-Hartmann device (35), 5 an image sensor (53) for capturing transmitted information received via the
Shack-Hartmann device, and for emitting signals derived from the captured information, a processing unit (55) coupled to and for receiving data from the image sensor, and for processing and delivering processed data, o characterized by : the source of illumination being triggered to emit at least one pulse of light as a flash lasting for a predetermined duration of time, the fast gate being opened into a first open state and being closed into a second closed state in predetermined synchronization with the at least one pulse of 5 light, and the processing unit being operated to derive a retina map from the data received from the image sensor via the fast gate.
29. Apparatus according to Claim 28, wherein: the source of illumination is configured to emit invisible light. 0
30. Apparatus according to Claim 28, wherein: the source of illumination is configured to emit visible light.
31. Apparatus according to Claim 28, wherein: the source of illumination is configured to emit coherent light.
32. Apparatus according to Claim 28, wherein: 5 the source of illumination is configured to emit white light.
33. Apparatus according to Claim 28, wherein: the source of illumination is configured to emit infrared light.
34. Apparatus according to Claim 28, wherein: the source of illumination (Sλn) is configured to emit light in a plurality of different discrete wavelengths (Sλl, Sλ2, ..., Sλn) and a discrete wavelength out of the plurality of different discrete wavelengths is controllably selected, whereby the source of illumination is triggered to emit at least one pulse of light in a at least one selected wavelength.
35. Apparatus according to Claim 28, wherein: the source of illumination (Sλn) is configured to emit light in a plurality of different discrete wavelengths (Sλl, Sλ2, ..., Sλn) and a discrete wavelength out of the plurality of different discrete wavelengths is controllably selected, whereby the source of illumination is triggered to emit a sequence of pulses of light including at least two different wavelengths.
36. Apparatus according to Claim 28, wherein: the source of illumination is controllable to focus illumination on either one of both the retina and a selected location in the interior of the eye.
37. Apparatus according to Claim 28, wherein: the duration of the at least one pulse of light lasts for less than one nanosecond.
38. Apparatus according to Claim 28, wherein: the fast gate is operated to open from the closed state into the open state within less than one nanosecond.
39. Apparatus according to Claim 28, wherein: the fast gate is operated to open from the closed state into the open state within less than 100 picoseconds.
40. Apparatus according to Claim 28, wherein: the fast gate is operated to close from the open state into the closed state before a next pulse of light is emitted in succession to the at least one pulse of light.
41. Apparatus according to Claim 28, wherein: reflections returned from the eye pass first via the gate and next via the Shack-Hartmann device.
42. Apparatus according to Claim 28, wherein: reflections returned from the eye pass first via the Shack-Hartmann device and next via the gate.
43. Apparatus according to Claim 28, wherein: a spatial pinhole filter (29) is disposed to receive reflections returned from the eye prior to passage of the reflections via the gate and the Shack-Hartmann device, to prevent capture of stray rays of light.
44. Apparatus according to Claim 28, wherein: a driver is coupled to the gate and to the source of illumination for synchronization of mutual operation of the gate and of the source of illumination, and the driver triggers the source of illumination to emit the at least one pulse of light in repetitive succession.
45. Apparatus according to Claim 28, wherein: a driver is coupled to the gate and to the source of illumination for synchronization of mutual operation of the gate and of the source of illumination, the driver triggers the source of illumination to emit the at least one pulse of light in repetitive succession, and the fast gate is operated to open into an open state and to close into a closed state in predetermined synchronization with the at least one pulse of light.
46. Apparatus according to Claim 28, wherein: a driver is coupled to the gate and to the source of illumination for synchronization of mutual operation of the gate and of the source of illumination , and the processing unit is coupled to the driver for control and management of retina mapping.
47. Apparatus according to Claim 28, wherein: a monitor is coupled to the processing unit for displaying data received from the image sensor as at least one image derived from the retina.
48. Apparatus according to Claim 28, wherein: the gate and the source of illumination are selected to match in wavelength.
49. Apparatus according to Claim 28, wherein: each at least one pulse of light is limited to a duration short enough to ensure that a second reflection returned from the eye as a retinal reflection will reach the gate after termination of a first reflection returned from the eye as a first reflection from the cornea and from the lens, to permit time domain discrimination between the first reflection and the retinal reflection, a driver is coupled to the gate and to the source of illumination for synchronization of mutual operation of the gate and of the source of illumination, and the driver controls the gate to remain in the closed state and to deny passage of each one first reflection pulse, and then controls the gate to open from the closed state into the open state and to permit passage of each one of the second reflection pulses being reflected from the retina, whereby the image sensor receives only second reflection pulses reflected from the retina.
50. Apparatus according to Claim 49, wherein: the Shack-Hartmann device is operated to derive aberration measurement of the cornea and of the lens of the eye under examination, and the processing unit is configured to correct each one of the second reflection pulses for aberration due to the cornea and to the lens by help of the derived aberration measurement, whereby the processing unit which is coupled to a monitor provides net retina reflection data derived from the second reflection pulses which are corrected for eye aberration.
51. Apparatus according to Claim 28, wherein: reflections reflected from the eye are directed to pass through a pinhole of small dimension pertaining to a spatial pinhole filter having a first side and a second side, and the gate is supported on either one of both the first side and the second side of the pinhole filter to receive reflections, and the gate is configured to match the small dimension of the pinhole, whereby a gate of small dimension is operable for mapping the retina.
52. Apparatus according to Claim 28, wherein: a portion of the reflections returned from the eye are deflected toward a color imager (63), and the color imager is coupled to a color monitor for displaying color images of the retina, whereby a color image may be superimposed on a reconstructed 3D retinal morphology.
53. Apparatus according to Claim 28, wherein: a portion of the reflections returned from the eye are deflected toward a color imager is coupled to the processing unit and to a monitor, and the processing unit is operated for image processing and for derivation of a retina map from the data received via the image sensor, whereby the processing unit is operative for displaying monochrome images on the monitor and color images on the color imager, and to provide monochrome images alone and in superposition with color images on the color imager.
54. Apparatus according to Claim 28, wherein: a total reflection prism is disposed to receive and transmit reflections returned from the eye, and is configured to deflect the received reflections into three separate channels, each channel out of the three channels is oriented in one direction different from the direction of the other two channels, and each channel carries only one single wavelength different from the wavelength of the other two channels, each channel operates a separate aggregation of equipment aligned along the direction of the respective channel, the equipment including one Shack-Hartmann device, one pinhole filter, one gate selected to match the wavelength of the respective channel, and one image sensor, a driver being is coupled to each one gate out of the three channels and to the source of illumination for synchronization of mutual operation of the three gates and of the source of illumination, and for triggering the source of illumination to emit the at least one pulse of light in repetitive succession, and the processing unit is being coupled to each one of the three image sensors and to a monitor, whereby images derived from the retina in real time in three different wavelengths are displayed alone and in superposition on the monitor as a 3D map of the retina corresponding to the three different wavelengths of the total reflection prism.
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