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
  • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
  • A61B3/1005—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for measuring distances inside the eye, e.g. thickness of the cornea
• • 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
  • A61B3/113—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for determining or recording eye movement
• • 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
  • A61B3/102—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for optical coherence tomography [OCT]
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
  • G01B9/02002—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies
  • G01B9/02004—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies using frequency scans
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
  • G01B9/02007—Two or more frequencies or sources used for interferometric measurement
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02015—Interferometers characterised by the beam path configuration
  • G01B9/02027—Two or more interferometric channels or interferometers
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
  • G01B9/02075—Reduction or prevention of errors; Testing; Calibration of particular errors
  • G01B9/02076—Caused by motion
  • G01B9/02077—Caused by motion of the object
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02083—Interferometers characterised by particular signal processing and presentation
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/0209—Low-coherence interferometers
  • G01B9/02091—Tomographic interferometers, e.g. based on optical coherence
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02097—Self-interferometers
• • 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
  • A61B3/117—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for examining the anterior chamber or the anterior chamber angle, e.g. gonioscopes
  • A61B3/1173—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for examining the anterior chamber or the anterior chamber angle, e.g. gonioscopes for examining the eye lens
• • 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
  • A61B3/12—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for looking at the eye fundus, e.g. ophthalmoscopes
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
  • G01B2290/45—Multiple detectors for detecting interferometer signals
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
  • G01B2290/70—Using polarization in the interferometer

Definitions

• the invention relates to an SS-OCT interferometer device for measuring a sample, in particular an eye, wherein the device generates a measuring signal inteferometrically by means of spectral tuning of the central wavelength of a measuring radiation and therefrom a depth-resolved contrast signal of the sample and to a Having control device.
• the invention further relates to an SS-OCT method for measuring a sample, in particular an eye, wherein interferometrically by means of spectral tuning of the central wavelength of a measuring beam a measuring signal and therefrom a depth-resolved contrast signal of the sample is produced.
• OCT Coherence tomography
• Embodiment corresponds to the image acquisition forth a so-called.
• A-scan ultrasound image acquisition it is also called optical coherence domain reflectometry (OCDR) designated.
• OCT optical coherence domain reflectometry
• OCT For OCT, essentially three variants are known: In the time-domain OCT, the eye is illuminated with a short-coherent radiation, and a Michelson interferometer ensures that backscattered radiation from the eye can interfere with radiation that has passed through a reference beam path.
• This principle already described relatively early in Huang, et al., Science 254: 1178-1181, 1991, can achieve a depth resolved image of the sample when the length of the reference beam path is adjusted, thereby corresponding to the coherence length of the radiation used Window in the sample is adjusted. The size of this window defines the maximum achievable depth resolution. For a good depth resolution, short-coherent, ie. spectrally wide radiation sources required.
• the length of the reference beam path is no longer changed, instead the radiation brought to the interference is detected spectrally resolved.
• the depth information of the sample i. the depth-resolved contrast signal is calculated from the spectrally resolved signal.
• the FD-OCT technique is able to measure simultaneously at all depths of the sample.
• Lighting source is spectrally tuned. This procedure is by the higher
• the problem remains, especially in the SS-OCT, that the widest possible spectral tuning range must be traversed, and this with a very narrowband radiation source.
• the run should be as fast as possible in order to keep the measuring time short.
• the sources satisfying these requirements in the field of eye measurement e.g. allow to determine the eye length sufficiently accurate, are very complicated and expensive.
• cheaper tunable laser beam sources are tunable thermally or over the stream, but the latter have very limited tuning ranges (e.g., 1-2 nm) and unfavorable spectral characteristics.
• the invention is therefore based on the object, a SS-OCT interferometer device or an SS-OCT method of the type mentioned so that measurements in the eye length with sufficient resolution are possible.
• This object is achieved by a SS-OCT interferometer device of the type mentioned, wherein the device comprises a sample movement detector which provides a motion signal indicating movements of the sample or in the sample, and in that the control means before or during the generation of depth-resolved contrast signal corrects the measurement signal by means of the movement signal with respect to measurement errors caused by the movement of the sample or in the sample occurred during the tuning.
• sample movement is meant here also a change in position of the sample, so that the sample movement detector can also be a position change detector.
• the object is further achieved by an SS-OCT method of the type mentioned above, wherein movements of the sample or in the sample detected and this indicating movement signal are generated and before or during the generation of the depth-resolved contrast signal, the measurement signal by means of Motion signal to be corrected for measurement errors caused by occurred during the tuning movements of the sample.
• the invention distances itself from the approach taken in the prior art of keeping the measuring time so short that movements of the sample, in particular pulsations of the eye, are negligible, and takes precautions to correct measuring errors caused by sample movements, by: for the device according to the invention a sample movement detector which provides a movement of the sample or in the sample indicating movement signal, or in the case of the device according to the invention a corresponding movement detection is used.
• the motion signal thus obtained is then preferably not simply used to correct the depth-resolved contrast signal, as would be possible, for example, in a simple eye tracking system, but with the motion signal is the interferometrically obtained measurement signal resulting from the tuning of the Meßstrahlungsario , corrected accordingly.
• the correction thus preferably starts before a transformation which converts the interferometric measurement signal into a depth-resolved
• correction signal is partly due to the fact that tracking on moving sample parts in motion detection is unnecessary.
• the term "fixed distance” refers to the optical path length to the detection / detector. This makes it possible to work with a spatially fixed sample movement detection or a sample movement detector, which manages without tracking.
• the correction signal then indicates only the contrast change in the reference section, which is then used to correct the measurement signal.
• a particularly strong contrast change is obtained if the reference section in the sample includes a surface of the sample or an interface of the sample, since then even a small sample movement leads to a strong signal change.
• the motion signal is then particularly easy to correct the measurement signal, if it is of the same kind, so is an interference signal. It is therefore particularly preferred if the sample movement detection is effected in an interferometric manner in an analogous manner, such as the generation of the measurement signal. It is therefore preferred that the sample movement detection is interferometrically by means of correction radiation spectrally determined in the central wavelength, since then changes in the correction signal can be used very simply to correct the measurement signal.
• the interferometric realization for generating the measurement signal and the correction signal can in principle use any suitable interferometer structure.
• the size to be measured then results from the phase change rate of the measurement signal.
• the detection of the phase change of the correction signal then allows a correction to sample movement. This is especially true for embodiments which work with a fixed reference in the form of a stationary reference object, e.g. for an interferometer with a reference beam path at the end of which there is a reflector that does not automatically move with the sample.
• an interferometrically obtained correction signal is also possible in embodiments which use as reference a point of the sample itself. Then, variations in distances within the sample are corrected, as may occur, for example, in eye length measurements.
• variations in distances within the sample are corrected, as may occur, for example, in eye length measurements.
• an eye length measurement for example, the reflexes of the anterior surface of the cornea and the fundus of the eye are coherently superimposed, both in the measuring channel and in the correction channel.
• the temporal phase change of the measurement signal (phase change rate) originates essentially from the tuning of the source and is directly proportional to the tuning speed and the eye length. If the eye length changes during the measurement, an additional (additive) phase change occurs.
• the interference capability can be achieved, for example, by using light sources of sufficient coherence length or, if the coherence length of the light source is insufficient, by using known pre- or post-interferometers (eg DE 3201801 C2).
• a Michelson arrangement is particularly preferred, so that the apparatus has a sample beam path, illuminates the sample by a part of the measuring radiation emitted by the measuring radiation source, and has a detection beam path which superimposes measuring radiation reflected or backscattered by the sample as sample measuring radiation receives and detected by means of a detector means, and the sample movement detector comprises a correction radiation source emitting the correction radiation, wherein a portion of the correction radiation is coupled into the sample beam path and illuminates the sample, and the detection beam path from the sample as sample correction radiation reflected or backscattered correction radiation receives and detected by the detector device separately from the measuring radiation, and the control device generates the correction signal from signals of the detection of the correction radiation.
• a correction radiation source is advantageous, which emits mono-modal laser radiation.
• the procedure is analogous to the fact that the sample is illuminated with a portion of the measuring radiation, and from the sample reflected or backscattered measuring radiation is detected, whereby a part of the correction radiation illuminates the sample, and reflected by the sample or backscattered correction radiation is detected independently and from this the correction signal is generated.
• This concept can be extended by a reference beam path which passes through a part of the measuring radiation emitted by the measuring radiation source as reference measuring radiation.
• the detection beam path then superimposes the sample measuring radiation with the reference measuring radiation.
• a portion of the correction radiation as reference correction radiation passes through the reference beam path and is superimposed in the detection beam path with the reference correction radiation.
• the sample is illuminated both with measuring radiation and with correcting radiation.
• Measurement and correction radiation backscattered or reflected on the sample is optionally superimposed with measuring and correction radiation which has passed through a reference beam path.
• the detector device always picks up a corresponding interference signal, with sample measurement radiation and correction radiation being detected independently, ie separately. From the Detection of the sample measuring radiation, the measurement signal is obtained, from the detection of the sample correction radiation, the correction signal.
• the wavelength of the measuring radiation is tuned, the central wavelength of the correction radiation, however, remains constant, so that the interference comes from a certain and during the measurement relative to the OCT unmodified volume that corresponds to the reference section.
• its location in or on the sample will change as a result of sample movements, e.g. described in DE 3134574 C2 and there removable for the skilled person. This document is therefore expressly incorporated herein.
• spectral and a polarization separation are possible.
• Other alternatives include geometric separation (e.g., pupil separation), multiplexing (e.g., alternately turning on the sources), and modulation and filtering at different frequencies.
• ⁇ ⁇ denote the wavelength of the correction radiation
• ⁇ M the wavelength of the measuring radiation
• n ( ⁇ ) the wavelength-dependent refractive index
• the separation of the signals in amplitude and phase function can be done particularly easily by means of a heterodyne detection.
• a quadrature component detection is applicable, as described for example in US 2004/0239943.
• the measurement radiation and the correction radiation are respectively modulated around their central wavelength. This modulation can be applied, for example, to a supply current of the measuring and correction radiation source, preferably with a stability of the supply current generation better than 0.8 ⁇ A, if an ophthalmological eye length measurement is to take place.
• a stability of the power supply of better than 0.8 ⁇ A corresponds to a coherence length of 100 mm.
• ⁇ > 0.015 nm follows.
• a shift of the wavelength as a function of the current in the described example source 0.21 nm / mA, this corresponds to a minimum current modulation of 70 ⁇ A.
• a rescaling of the amplitude function of the measurement signal can take place before the generation of the contrast signal.
• the amplitude function as a function of time is determined from the intensity of the interferences in the modulation.
• Amplitude correction means that the amplitude at time t is always at a constant value, e.g. the initial value A (to) is corrected. This is a prerequisite, if one then wants to evaluate the signal with a Fourier transformation.
• the procedure according to the invention makes it possible to use radiation sources for the SS-OCT, which are significantly more cost-effective and could not hitherto be used due to their tuning rates.
• radiation sources are: External Cavity Diode Lasers, Distributed Feedback Lasers, Distributed Bragg Reflectors Lasers, Vertical Cavity Surface Emitting Lasers, Vertical External Cavity Emitting Lasers.
• control device ensures that the device described carries out the corresponding method.
• the method features mentioned here are thus also features of the control device in the mode of operation of the control device.
• operating characteristics of the control device are to be understood as process features of the corresponding method.
• 1a is a schematic representation of an OCT for eye length measurement, wherein the OCT has an independent reference beam path,
• FIG. 1b shows an OCT similar to that of FIG. 1a, wherein the OCT of FIG. 1b has no reference beam path, but instead causes radiation reflected or backscattered from different depth ranges of the eye to interfere with each other
• FIG. 2 shows an OCT similar to that of FIG but with an interferometric sample motion detector
• FIG. 3 is an OCT similar to FIG. 2, but in a phased-optical construction
• FIG. 4 is a graph showing the wavelength characteristic of the lasers of the OCT of FIG. 2 or 3, as seen in the tuning of the central wavelength and in the context of a heterodyne. Detection results.
• FIG. 1 a shows an OCT 1 operating on the principle of a Michelson interferometer, which performs measurements on an eye 2 of a patient.
• this application of the OCT 1 is exemplary, and other measurement tasks can be performed with it, for example, transparent waveguide structures or other structures relevant to semiconductor technology can be measured. Also, the measurement of other biological tissue is possible.
• the operation of the OCT 1 is controlled by a control device 3, which is connected to the corresponding components of the OCT 1, drives them, reads out the measured values supplied by them and provides therefrom the desired imaging information about the sample, in this case the eye 2, and (not shown) brings to display or transmits corresponding data.
• a control device 3 which is connected to the corresponding components of the OCT 1, drives them, reads out the measured values supplied by them and provides therefrom the desired imaging information about the sample, in this case the eye 2, and (not shown) brings to display or transmits corresponding data.
• the OCT 1 has a measuring laser 4, which is designed as a VCSEL (Vertical Cavity Surface Emitting Laser). It emits spectrally narrow-band radiation, resulting in a coherence length of typically 100 mm (spectral width of 0.007 ⁇ m) at a wavelength of approximately 850 nm.
• VCSELs with e.g. 30MHz linewidth (Avalon Photonics), i. Realizable scan depths considerably larger than required for length measurements on the entire eye.
• the relationship between scan depth and line width is u.a. described by
• the central wavelength of the emitted from the measuring laser 4 measuring radiation 5 can be spectrally tuned by the operating temperature changed or the external cavity is suitably changed.
• a laser is disclosed, for example, in Chang-Hasnain, CJ. , "Tunable VCSEL", IEEE Journal of selected topics in Quantum Electronics, 2Q00, Volume 6, pages 978-987.
• the measuring radiation 5 is incident on a beam splitter 6, which allows a portion of the measuring radiation to pass into a sample beam path 7 leading to the eye 2. Another part of the measuring radiation 5 is derived from the beam splitter 6 in a reference beam path 8, at the end of a mirror 9 is.
• the sample 2 backscatters or reflects in different depth ranges the incident part of the measuring radiation 5, so that at the sample 2 reflected or backscattered radiation as sample measuring radiation in the sample beam path 6 counter to the direction of incidence of the measuring radiation 5 back to the beam splitter 6. This is symbolized by a double arrow for the radiation in the sample beam path 7.
• the part of the measuring radiation 5 that has passed through the reference radiation path 8 is at least partially transmitted at the beam splitter 6 and reaches a detection beam path 10 where it is superimposed with the sample measuring radiation, which is likewise introduced into the detection beam path 10 by the beam splitter 6.
• the parts of the measuring radiation superimposed in this way interfere with each other at the detector 11, which receives a corresponding interference signal and forwards it to the control unit 3.
• FIG. 1 b shows a variant of the OCT 1 of FIG. 1 a, which operates without reference beam path 8.
• 10 parts of the measuring radiation 5 which have been reflected or backscattered from different regions of the sample interfere, the maximum distance of the regions depending on the coherence length of the measuring radiation 5:
• the structures in the sample may only have distances. which are smaller than the coherence length of the sources used (otherwise the radiation does not interfere and the method does not work). What is more important, is that the structures must also have a distance greater than the depth resolution of the measurement method, which essentially results from the width of the maximum tuning range. Can the example described source at 850 nm by max.
• the construction of Fig. 1b has the advantage of better utilization of the measuring radiation used 5, since not, as in the construction of Fig. 1a, an additional selection of the interfering radiation by the path length of the reference beam path 8 is made. Otherwise, with regard to the invention described here, the variants of FIGS. 1 a and 1 b do not differ any further, so that the above or following description applies equally to both variants.
• the central wavelength of the measuring radiation 5 is tuned by suitable control of the measuring laser 4.
• the interference signal recorded by the detector 11 is then wavelength dependent as a measurement signal and the controller 3 can generate therefrom by Fourier transform a depth-resolved contrast signal on the contrast in the eye 2 along the direction of incidence of the measuring radiation 5, as is known for SS-OCT.
• SS-OCT-usual evaluation algorithms can be used.
• An eye length change or movement e.g. by pulse beat, respiration or microsaccades, however, leads to a change in the measurement signal, which is a movement artifact and falsifies the measurement signal and thus the contrast signal generated therefrom. Due to the tuning time required by the VCSEL in the measuring laser 4, such distortions can not be excluded when measuring the eye length, since the measuring time can be in the range of several seconds.
• the OCT 1 of Fig. 1a and 1b therefore, has a sample movement detector 12, which can be executed in the construction of Figures 1a and 1b, for example, as a known eye tracker, as it is used in eye surgery, and the movements of the eye , For example, the cornea front surface or the interface with the eye lens detected.
• the sample movement detector 12 supplies a corresponding movement signal to the control device 3, which displays this information about movements of the eye 2 or movements of structures in the eye 2.
• the sample movement detector can either supply a specific movement signal which indicates the direction and extent of the movement of the monitored structure.
• a correction signal is also possible as the movement signal, which merely reproduces a contrast value in a specific monitored sample volume, ie a specific reference section of the eye 2, this monitored section or reference section, of course, at a fixed distance from the OCT 1 lies. At a fixed distance is a fixed optical path length to the detector 1 1 along the sample beam path 7 and the detection beam path 10 to understand.
• the controller 3 uses the correction signal to correct the contrast signal. It is particularly preferred because of the computationally simple and at the same time combined with high accuracy that the control unit 3 corrects the measuring signal, ie the interference signal of the detector 11, by means of the correction signal before the contrast signal is generated by Fourier transformation.
• Fig. 2 shows a variant in the realization of the sample movement detector 12, which also works interf erometrically.
• the construction of Fig. 2 is based on the construction of Fig. 1b, but this is not to be understood as limiting.
• the sample motion detector of Fig. 2 may also be used in the construction of Fig. 1a.
• the sample movement detector 12 comprises a correction laser 13 which emits correction radiation 14 which is superimposed on the measuring radiation 5 via a beam splitter 15.
• the correction radiation 14 differs from the measuring radiation 5, so that later the superimposed radiation can be separated from each other again.
• the polarization or the wavelength can be used.
• the beam splitter 15 is then suitably designed as a pole splitter or as a dichroic beam splitter or combiner.
• the polarization-optical differentiation or separation and combination of measuring radiation 5 and correction radiation 14 is technically particularly advantageous because dichroic beam splitters are very expensive for closely adjacent wavelengths. Any influence of birefringence on the sample, for example on the anterior chamber of the eye 2, can be compensated by suitable compensators.
• the correction radiation 14 also falls on the eye 2, is reflected there or backscattered and enters the detection beam path 10.
• it is by a further suitably trained beam splitter 14 of the superimposed with her measuring radiation 5, which was also reflected by the eye or backscattered, separated and reaches an independent detector 17. So this detector is interfering in itself
• Correction radiation 14 from within the coherence length of the correction radiation 14 lying areas of the eye 2.
• the detector 17 thus provides a measurement signal 11 similar interferometric correction signal.
• the center wavelength of the correction radiation is not tuned so that interference of constant wavelength radiation exists.
• correction radiation 14 corresponds to that of the measuring radiation.
• a correction laser 13 are laser types in question, which can also be used for the measuring laser 4 application.
• the control unit 3 thus receives from the detector 17 a correction signal which is also an interference signal and similar in nature to the measurement signal from the detector 11.
• the correction laser is not tuned in its central wavelength but remains fixed.
• the correction signal is thus a measure of the temporal changes in length in a reference region B within the sample 2, which is defined by the coherence wavelength of the correction radiation 14 and the path lengths in the sample and detection beam path.
• the reference region B is spatially fixed relative to the OCT 1, ie it shifts correspondingly in the eye 2 during movements of the eye 2.
• movements in the eye 2 or movements of the eye 2 result in a change in the correction signal. so that the correction signal can be used to correct the measurement signal by modifying the measurement signal in opposition to the changes in the correction signal.
• the reflexes of the corneal anterior surface and fundus are coherently superimposed, both in the measurement and correction channels.
• the . temporal phase change of the measuring signal comes essentially from the tuning of the source and is directly proportional to the tuning speed and the eye length. If the eye length changes during the measurement, an additional (additive) phase change occurs.
• the central wavelength is not tuned, measuring the phase change by the change in the eye length separately and can thus correct the measurement signal, so that one can calculate from the corrected signal, the average eye length.
• the correction calculation takes place as explained above in the general part of the description.
• Fig. 3 shows a construction of the OCT 1 of Fig. 2 in fiber optic implementation.
• the beam splitter 15 is replaced by a fiber coupler 19
• the beam splitter 6 by a fiber coupler 20
• the beam splitter 16 by a fiber coupler 21.
• the construction of FIG. 3 corresponds to that of FIG. 2.
• the following development can be used for all embodiments, which starts from the knowledge that an eye length change or movement in the measurement signal as in the correction signal to a phase change due to the change in length and a change in amplitude due to the eye movement-related shift of a reflection or Backscatter site in the eye 2 leads. It is therefore possible in a development to distinguish between phase and amplitude change.
• a variant of this distinction is a heterodyne detection, in which the wavelength of both the measuring laser 4 and the correcting laser 13 is changed around the central wavelength so that the measurement signal just because of the interference of the reflections from different depths of the eye 2 of a maximum changed to the nearest minimum. It is advantageous if the measurement signal changes by at least twice the range in order to facilitate the evaluation (then one need not determine the range so accurately). From the difference of the two extrema can then the amplitude function of the measuring
• Fig. 4 shows the wavelength (in nm) as a function of time t (in arbitrary units).
• the wavelength profile 22 describes the measuring radiation 5, which is tuned from a value just below 850 nm to just under 852 nm, the curve 23, the correction radiation 14.
• Correction radiation 14 is continuously about 852 nm. Both wavelengths are modulated synchronously around the respective central wavelength, as shown by wavelength profiles 22 and 23 in the illustration of FIG. For the sake of clarity, FIG. 4 shows that the modulation is increased many times over, since otherwise they would not be recognizable.
• the modulation of the measuring radiation 5 and the correction radiation 14 by changing the supply current of the measuring laser 4 and the correction laser 13 causes can be done very quickly against any movement influences.
• the modulations around the central wavelengths are therefore extremely high-frequency compared to any effects of movement and thus virtually instantaneous. So they are not distorted by the influence of movement.
• phase function of the correction signal in the control unit 3 is subtracted from the phase function of the measurement signal. All amplitude changes are undesirable because of their origin from motion artifacts or potential variations in radiation intensity. It is therefore necessary to separate the amplitude fluctuations and the phase fluctuations.
• the evaluation then takes place as follows: One knows the phase function of the signal wave ⁇ s (tj) and the Phase function of the correction wave ⁇ k (tj) as a function of time. In addition, one knows the
• Eye length is. In this case one does not need the amplitude function and a Fourier transform.
• the contrast signal is now generated by means of Fourier transforms, which is then free of eye movement influences despite the comparatively long duration of the wavelength of the measuring radiation 5.
• Quadraturkomponentenbetician which also allows the division of the measurement signal and the correction signal in phase function and amplitude function, as is known from the reference mentioned above.

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