Classifications

• • 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
  • A61B3/0091—Fixation targets for viewing direction

Definitions

• the present invention relates to a sighting device for an examination of the eye. It also relates to an aiming method implemented in this device, as well as an in vivo tomography eye examination system equipped with this device.
• the residual movements during a fixation are of three types: - Physiological nystagmus (or tremor): very fast oscillations (from 40 to 100 Hz), of small amplitude (displacement of the micron images on the retina); - Drifts: slow movements (1 ⁇ m in a few ms), decorrelated from one eye to another; - Micro-saccades: very fast movements (a few hundred per second), correlated between the eyes, of approximate refocusing of the field.
• Physiological nystagmus or tremor
• very fast oscillations from 40 to 100 Hz
• small amplitude displacement of the micron images on the retina
• - Drifts slow movements (1 ⁇ m in a few ms)
• - Micro-saccades very fast movements (a few hundred per second), correlated between the eyes, of approximate refocusing of the field.
• the object of the present invention is to overcome these drawbacks by proposing a sighting device that optimizes the fixing performance of the subject, the aiming device being intended to equip an examination system by providing a very good spatial resolution. It is therefore a question of increasing the overall performance of the examination by increasing that of the subject.
• the aiming device comprises at least one moving target having a shape and a programmable trajectory, this or these targets being displayed on viewing means such as a screen and visible from both eyes during the examination. In a first operating mode, the target or targets are moved so as to alternate fixing intervals at a given position with so-called rest intervals on one or more other positions.
• the duration of the fixing intervals can be adjusted to optimize the quality. It is also possible to adjust the diversity, the position and the duration of the rest positions.
• a continuous movement is controlled which forces the subject's gaze to follow a moving target. If the tracking performance is better than that of fixation, the prior knowledge of the trajectory would make it possible to read the images of the eye obtained with a better precision than they are when one observes a still target.
• an in vivo tomography eye examination system comprising: - a Michelson interferometer, performing a full field OCT assembly, - an adaptive optics device, disposed between the interferometer and an eye to be examined, performing correction of the wave fronts from the eye but also to the eye, and - a detection device, disposed downstream of the interferometer, allowing without modulation or synchronous detection, to perform the interferometric measurement according to the principle of OCT, characterized in that it further comprises a sighting device according to the invention, comprising at least one moving target having a shape and a programmable path said target being displayed on viewing means and visible from at least one of said patient's eyes during the examination period.
• FIG. 1 illustrates the structure of an in vivo tomography system incorporating an aiming device according to the invention
• FIGS. 2A and 2B respectively represent a first and a second embodiment of active patterns implemented in a device of FIG. referred to according to the invention, on a computer screen.
• FIG. 3 is a diagram of another exemplary embodiment of an in vivo tomography system according to the invention.
• the system includes a Michelson interferometer having a measuring arm for illuminating the eye and collecting the reflected light, and a reference arm for illuminating a movable mirror for deep exploration of the retinal tissue.
• the interferometer is used in rectilinear and perpendicularly polarized light in both arms.
• the light source S is a diode with a small temporal coherence length (for example, 12 ⁇ m) whose spectrum is centered on 780 nm.
• the two arms have a configuration called Gauss, afocal, which allows the transport of the pupils, on the one hand, and the materialization of an intermediate image of the field where a diaphragm blocks a large part of the corneal reflection, on the other hand.
• Quarter wave plates provide by rotation of the polarization of the single light reflected by the eye, and the moving mirror, effective filtering parasitized reflections in the in vivo tomography system according to the invention.
• the reference arm is similar to the measuring arm, but with static optics. The detection path of the in vivo tomography system according to the invention will now be described.
• the two beams on the output arm are still polarized perpendicularly, and they interfer only if they are projected on a common direction.
• a prism of Wollaston W has the function of simultaneously projecting the two radiations on two perpendicular directions of analysis. It is then possible to perform a simultaneous measurement of the intensity after interference in two opposing interference states, without modulation or synchronous detection, on a single two-dimensional detector.
• the addition of a quarter wave plate, after division of the beam allows access to two additional measurements, thus removing any ambiguity between amplitude and phase of the fringes.
• a half-wave plate at the entrance of the detection channel makes it possible to correctly orient the incident polarizations.
• the Wollaston prism is placed in a pupillary plane, thus conjugated with the separator cube of the Michelson interferometer.
• the angle of separation of the Wollaston prism is chosen according to the field to be observed.
• the focal length of the final lens determines the sampling rate of the four images.
• the detector is of the CCD type, with an image rate of more than 30 frames per second. This detector is associated with a dedicated computer (not shown) in which digital image processing is performed: extraction of the four measurements, calibration, calculation of the amplitude of the fringes.
• the adaptive correction of the wave fronts is performed upstream of the interferometer, thus in the measuring arm. Each point of the source S thus sees its image on the corrected retina of the aberrations, and the image in return is also corrected.
• the adaptive optics subsystem includes a deformable mirror MD.
• the ⁇ wavefront measurement is made by a Shack-Hartmann SH analyzer on the return beam of a light spot itself imaged on the retina via the deformable mirror MD.
• the wavelength analysis is 820 nm.
• the illumination is continuous and provided by a temporally incoherent superluminescent SLD diode.
• the sizing of the analyzer corresponds to an optimization between photometric sensitivity and sampling of the wavefront.
• the rate of refreshing of the control of the deformable mirror MD can reach 150 Hz.
• a dedicated computer (not shown) manages the adaptive optics loop. The control is however synchronized to freeze the mirror shape during the interferometric measurement.
• the deformable mirror MD is conjugated with the pupil of the system and the eye.
• the system field is defined by the system input DCM field iris. It is preferably chosen at a value lower than that of the isoplanetism field of the eye, which guarantees the validity of the adaptive correction in the field on the only wavefront measurement made from the spot, in the center of the field.
• the field of the system can be chosen equal to 1 degree, but the value of this field could be increased.
• the rotation of the deformable mirror MD makes it possible to choose the angle of arrival of the beam in the eye, and thus the portion of retina studied.
• corrective lenses from the view of the subject, so low orders of geometric aberrations such as focus or astigmatism, just in front of the eye, allows to relax the requirements on the path of the deformable mirror MD, and guarantees also a better aim.
• a transmission adaptive corrector system may be used in preference to fixed lenses for optimal correction.
• the system may furthermore comprise conventional imaging means, such as an IMG camera, making it possible to associate the interferometric measurements with a simple imaging of the areas examined, for example to facilitate the exploration and selection of the areas to be examined.
• a second polarizing cube CNPI makes it possible to divert the return beam towards an IMG imaging camera having its own means of LI focus of the image. On this path, a direct image of the targeted retinal area will be observable.
• the measuring arm and this additional channel so that they provide a wider field of observation than the interferometric mode, the field of which is limited in particular by the interferometric contrast measurement technique itself.
• a sighting device according to the invention, collaborative or active, is installed upstream of the assembly.
• This aiming system which includes an active MAM pattern, presents to the subject the image of a light point that departs periodically from the desired line of sight. The patient is then invited to follow all the movements of this image. Each time the image returns to the axis, and after an adjustable latency time, a series of interferometer measurements is performed. The periodic displacement of the gaze makes it possible to obtain from the patient a better fixation capacity when he aims at the desired axis. The amplitude and the frequency are adaptable to the subject and the measures undertaken. For the sake of convenience, the test pattern can be performed with a simple desktop computer on which a bright spot is displayed and moved.
• the active MAM pattern, adaptive optics, S source, and image capture are synchronized.
• a graphical user interface IA or IB comprises, for example, a first window FI for managing a spot, a second window F2 for continuous shooting, and a moving target CA or CB on a zone of the screen.
• This moving target can be realized for example in the form of a conventional representation target consisting of a set of concentric circles and a cross of sight in the center of these circles (FIG. 2A), or else in the form of a graduated cursor and a superimposed sighting cross (Figure 2B) In the example illustrated in FIG.
• the system is arranged so that the target of the active MAM pattern is visible by the two eyes OD1 and OG1 of the subject to be examined.
• a sight with both eyes can indeed improve the performance of fixations or stability, and facilitate the examination.
• the image of the pattern is introduced into the optical path between the reference source SLD and the eye examined by a separator BST3.
• This splitter can be chosen dichroic so as to reflect 50% of all the light coming from the MAM pattern toward the examined eye OEX, and transmit the remaining 50% to the other eye OV1 or OV2 to allow a sighting of both eyes.
• the dichroic splitter BST3 then transmits all of the light from the SLD reference source to the examined eye OEX, taking advantage of a spectrum difference between the reference source SLD (830 nm) and the MAM pattern (800 nm).
• a 50/50 beam splitter that is completely neutral spectrally is also suitable, but 50% of the SLD light is then sent to the eye that is not studied.
• a filter can eliminate this image if it is considered troublesome by the subject.
• the system has a central OEX examination location, as well as two OVl and OV2 sighting locations on both sides of this location. OEX exam.
• the system may also include, or collaborate with, IRIS tracking means of movements of the eye to be examined, collaborating with the tomography device. It may be for example a camera with image recognition performing tracking or "tracking", for example of the retina or pupil or edges of the iris, so as to detect and evaluate the movements of the 'eye.
• Knowing the movements of the eye then allows the system to adapt to the movements of the area to be examined, for example by coordinating and setting and shooting with the different detected or predicted positions of this area to be examined, or by allowing a spatial and / or temporal optimization of the adaptive optics. It is possible for example to take advantage of the natural periods of stabilization of the pupil or the retina to achieve all or part of the adjustments or desired measurements.
• the image of the examined eye reaches the IRIS eye tracking means by a BST2 splitter inserted in the optical path, for example between the eye and the SLD reference source.
• this separator BST2 is dichroic and the monitoring of the movements of the eye is in non-visible light, for example infrared.
• the IRIS tracking means may comprise for example a device for measuring eye movements, such as those developed by the company Mozovision.
• the invention may in particular be implemented to make or complete a retinal imaging device, or corneal topography, or measuring a film of tears.
• the invention is not limited to the examples that have just been described and many adjustments can be made to these examples without departing from the scope of the invention.

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• 2004
  • 2004-01-22 FR FR0400581A patent/FR2865371B1/fr not_active Expired - Fee Related
• 2005
  • 2005-01-21 US US10/586,839 patent/US7438415B2/en not_active Expired - Fee Related
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