OCT-based spatially resolved transmittance measurements of the eye

Abstract

A method for measuring at least one parameter indicative of the optical transmission quality of an eye (30), such as information about absorbing or scattering structures affecting the light propagation between the cornea and the retina and / or information about the imaging quality, e.g. the point spread function (PSF) of the eye, is described. The method comprises recording a plurality of optical coherence tomography A-scans of different corneal positions xi,yi of the eye (30) by means of an optical coherence tomography device (10-18) and a scanner (24a, 24b). For each A-scan, a reflection value at the retina of the eye is determined. The reflection values can then be combined, e.g. for displaying an image of the transmission quality of the eye as a function of xi,yi, or for determining the point spread function (PSF) of the eye by means of Fourier analysis.

Description

Technical Field

[0001] The present invention relates to a method for measuring at least one parameter indicating the light transmission quality of the eye, such as information about the absorption or scattering structures that affect light propagation between the cornea and retina and / or information about image quality, for example, the eye's point spread function (PSF). Background Technology

[0002] EP 2710950 describes a method for measuring intraocular scattering, specifically by illuminating the eye with a ring or circular beam of light and measuring its reflection from the retina to measure the eye's point spread function (PSF).

[0003] Such a method requires complex measurements to eliminate the reflection effect from the front of the eye and derive the eye's PSF. Summary of the Invention

[0004] The problem to be solved by the present invention is to provide a method of this type that can reliably measure at least one parameter indicating the optical transmission quality of the eye.

[0005] This problem is solved by the method and apparatus of the independent claim.

[0006] Therefore, the method includes at least the following steps:

[0007] - Record multiple OCT A-scans for different corneal locations xi,yi on both sides of the eye: In other words, perform multiple optical coherence tomography measurements by sending a beam of light through different corneal locations.

[0008] - For each of the A-scans, the reflectance value ri at the retina of the eye is identified: this reflectance value indicates the amount of light reflected from the retina and returned to the OCT measurement system.

[0009] - Use the reflection value ri and the position xi,yi to determine one or more parameters: In other words, the reflection value ri and their coordinates xi,yi are processed to determine the parameters.

[0010] Therefore, optical coherence tomography data can be recorded for each A-scan. This allows for easy differentiation of reflectance values ​​originating from the front of the eye and the retina, i.e., isolating the reflectance value ri from the retina. The reflectance value ri depends on the transmission characteristics of the eye at position xi,yi along the corresponding A-scan, which allows for obtaining a spatially resolved indication of how well the eye can transmit light along the probe beam of A-scan i.

[0011] This information can be used to determine a large number of different parameters. Some examples include:

[0012] - The parameters can describe at least one aspect of the eye's point spread function (PSF). For example, the method may include steps of determining a one-dimensional or two-dimensional representation of the point spread function using the reflection value ri, and / or it may convey the same characteristics, such as its half-width along one or more directions.

[0013] - Parameters can describe the absorption and / or scattering structures in the anterior segment of the eye. For example, the method may include the following steps: determining the location and / or spatial extent of the absorption and / or scattering structures in the anterior segment of the eye using the reflectance value ri, particularly along xi and / or yi, for example by representing the reflectance value ri as an image in xi-yi space.

[0014] Advantageously, multiple A-scans, including the first multiple A-scans, preferably at least 10 A-scans, and particularly at least 100 A-scans, have parallel incident directions. In other words, the A-scans differ only in their positions xi,yi, but not in the direction of the external beam illuminating the cornea. This allows recording the eye's transmission characteristics to light from a given direction. Furthermore, for eyes adapted to infinity, all such A-scans will essentially be incident on the common location of the retina, thus providing better robustness for measuring retinal reflexes with spatial variations.

[0015] In particular, the “parallel incident direction” may be parallel to the visual axis of the eye, which allows for the recording of transmission characteristics along the patient’s natural viewing direction.

[0016] In this context, "parallel" is advantageously understood to include parallelism within 5°, and especially within 1°.

[0017] Advantageously, the A-scan includes multiple A-scans, preferably at least 10, and particularly at least 100, that do not overlap at the cornea of ​​the eye. In other words, these A-scans enter the eye at different locations, allowing information to be recorded with good spatial resolution.

[0018] In this context, it is advantageous that if the center-to-center distance between two A-scans on the cornea is greater than their half-width diameter, then they do not overlap. The "half-width diameter" is the diameter in the xy-plane outside the eye, perpendicular to the A-scan direction, at which the light intensity used for the A-scan decreases by 50%.

[0019] In another important embodiment, at least a portion of the A-scan probe beam is focused onto the front of the eye, i.e., the probe beam has its minimum diameter at that front. This allows for spatial resolution of scattering or structures within that part of the eye.

[0020] In this context, if the minimum diameter of the probe beam of the A-scan is within the range of 1m anterior to the cornea and 5mm posterior to the lens of the eye, then it is advantageous to consider that the A-scan is focused on the anterior part of the eye.

[0021] Alternatively or additionally, for at least a portion of the probe beam, the focal point may also be located between the posterior surface of the eye's lens and the retina. This could be useful, for example, for detecting vitreous floaters.

[0022] In one embodiment, the invention includes the step of displaying the reflectance value ri as a function of the location xi, yi. Therefore, the displayed image represents the reflectance value ri as a function of xi and yi. For example, the image may include pixels, where pixel coordinates are mapped to coordinates xi, yi and pixel color and / or brightness are functions of the reflectance value ri. Such an image allows for the determination of locations, for example, areas where light transmission through the eye is poor due to scattering and / or absorption.

[0023] For example, this allows for the determination of the location of absorption structures in the anterior part of the eye. Again, for example, the anterior part of the eye can be the portion between the cornea and the posterior aspect of the lens of the eye, about 5 mm behind it.

[0024] To achieve good lateral resolution of absorbing or scattering structures in the vitreous, it is advantageous to place the focal point between the posterior surface of the lens and the retina.

[0025] In another embodiment, the present invention includes a Fourier analysis of a dataset ri(xi, yi). This Fourier analysis includes at least the following steps:

[0026] - Perform a Fourier transform on the dataset based on the reflectance value ri: The dataset can be, for example, the dataset ri(xi, yi), where a Fourier transform is performed along at least one dimension of the xi-yi space. For example, it can also be ri(θxi, θyi), where θxi and θyi are the horizontal and vertical angles relative to the optical axis or visual axis of the eye, respectively, of the propagation direction of the probe beam entering the eye at xi,yi on the posterior side of the lens.

[0027] - Derive the at least one parameter from the result of the Fourier transform: for example, the result may be a Fourier component of the point spread function describing the eye along at least one direction, or it may be a parameter derived from the Fourier component, such as the width (e.g., half-width) or contrast (e.g., the ratio of peak amplitude to background noise) of the PSF in at least one direction.

[0028] Advantageously, a two-dimensional Fourier transform is used, which allows the PSF (or its parameters) to be evaluated in two dimensions.

[0029] Alternatively, or in addition to using Fourier transform, ray tracing can be used to calculate PSF, which allows for consideration of the eye's refractive structure, particularly its aberrations, as these can be determined, for example, by means of OCT measurements.

[0030] The method may also include at least one of the following steps:

[0031] - The axial length of the eye between the pupil and retina is determined from an A-scan using optical coherence tomography; this data can be easily derived from the A-scan.

[0032] - Determine the diameter of the pupil: This data can also be easily derived from an A-scan or with the aid of a calibrated microscope.

[0033] Additionally, data from the A-scan can be used to extract the topological structure of at least one structure of the eye. For example, this structure can be at least one of the following:

[0034] -cornea,

[0035] -Iris,

[0036] - The anterior surface of the lens, and / or

[0037] - The posterior surface of the lens.

[0038] In that case, the method may also include a step of determining at least one parameter using the reflection value ri and the topology of the structure, for example, using ray tracing calculations.

[0039] The present invention also relates to an ophthalmic device, including

[0040] - Optical Coherence Tomography Interferometer: This OCT interferometer is used to record A-scans.

[0041] - A control unit configured and adapted to perform the methods described herein: This control unit has suitable software and hardware for performing the steps of the invention. It may also include a display, storage, and / or data interface for displaying, storing, and / or transmitting data determined by the present technology. Attached Figure Description

[0042] The invention will be better understood when the following detailed description is considered, and other objects besides those described above will become apparent. This description refers to the accompanying drawings, in which:

[0043] Figure 1 A schematic configuration of an embodiment of an ophthalmic device is shown.

[0044] Figure 2 An example of a scanning mode is shown.

[0045] Figure 3 The reflectance values ​​obtained in the A-scan are shown.

[0046] Figure 4 A cross-sectional view of the eye is shown, with two A-scan incident light traces.

[0047] Figure 5 The corneal reflectance values ​​ri as a function of xi, yi are shown for four different eyes A, B, C, and D.

[0048] Figure 6 The diagram shows the images for eyes A, B, C, and D. Figure 5 The PSF (point spread function) obtained from the reflection value ri in the image, and

[0049] Figure 7 The images shown are for eyes A, B, C, and D. Figure 6 The intensity values ​​of PSF along the horizontal (PSF H, u) and vertical (PSF V, v) directions.

[0050] (Note: All grayscale images in the figure have been halftoned to improve reproducibility. Halftoning is generally not used when displaying images on electronic monitors.) Detailed Implementation

[0051] Equipment Overview

[0052] Figure 1 Ophthalmic equipment includes, for example, ophthalmic microscopes with OCT capabilities.

[0053] It includes the optical coherence tomography interferometer 10-26.

[0054] The interferometer has a light source 10, which in this embodiment is a swept-frequency light source, that is, it generates narrowband light whose wavelength can be adjusted.

[0055] Light from light source 10 passes through beam splitter 12, particularly fiber optic beam splitter, and is sent to two interferometer arms 14, 16.

[0056] The first arm is a reference arm 14, which includes a collimating lens 17 and a reflector 18 at one end. Light striking the reflector 18 is sent back to the beam splitter 12 and from there at least partially to the photodetector 20.

[0057] The second arm is the sample arm 16. It includes a collimating optics 22 for collimating the probe light from the beam splitter 12. The light is then fed through two scanning mirrors 24a, 24b and an objective lens 26 to generate a probe beam 28. Depending on the positions of the scanning mirrors 24a, 24b, the probe beam 28 can be laterally offset in the xy plane perpendicular to the optical axis z of the device.

[0058] In this embodiment, an interferometer is used to generate the telecentric probe beam 28, i.e., probe beam 28 for various x and y coordinates (such as... Figure 1 Beams 28 and 28' are parallel to each other. This can be achieved by placing the pivot point of the scanning system approximately on the back focal plane of lens 26. The telecentric scanning geometry simplifies the analysis within the technical context described below.

[0059] In the illustrated embodiment, the probe beams are shown focused on the anterior surface of the cornea, but they could also be focused on any other part of the eye 30 of particular interest. For the reasons mentioned above, the probe beams are advantageously focused on the anterior segment of the eye.

[0060] The position and / or power of focusing optics, such as lenses 22 and / or 26, can be adjustable to change the position of the focal point along the z-direction.

[0061] The probe beam 28 enters the eye 30, where it is reflected or scattered by the eye's structure. The light reflected back from this structure returns to the beam splitter 12, where it can interfere with the light from the reference arm 14, and from there reaches at least partially the photodetector 20.

[0062] Figure 1 The device operates by recording multiple A-scans. For each such A-scan i, the probe beam 28 is directed to the desired xi- and yi- positions by means of scanning mirrors 24a, 24b. The center wavelength of the light source 10 is then tuned within a given wavelength range, which is typically much wider than the spectral width of the light from the light source 10. The light at the photodetector 20 is measured as a function of the center wavelength.

[0063] Spectral analysis, particularly Fourier transform, of the signal from detector 20 can then be used to generate reflectance values ​​of eye 30 along axis z for a given A-scan. Reflectance values ​​are related to the aforementioned reflected and scattered light. Following OCT imaging conventions, reflectance values ​​can be represented by a value proportional to the reflected intensity, a value proportional to the logarithm of the reflected intensity, or, for example, other range-compressed values. In more general terms, "reflectance value" indicates the amount of light returning from a location along the A-scan. Advantageously, it can be linearly related to the amount of light, its logarithm, or any other function thereof.

[0064] This type of OCT measurement is known to those skilled in the art and is described, for example, in EP3572765 and the references cited therein.

[0065] The device also includes a control unit 32, which may include, for example, a microprocessor 34a, a memory 34b, and a display 34c. The memory 34b may store data and program instructions required to execute the steps of this method. For example, the display 34c may be used to display the data thus determined and, in particular, to display the plots or images described below.

[0066] Advantageously, the measurement range of the OCT interferometer 10-26 (for a single A-scan) extends at least from the cornea to the retina of a typical eye. In other words, depth-resolved information of at least 40 mm (in air) can be obtained with a single A-scan (i.e., for SS-OCT with a single light source scan). This allows the application of the techniques described below along the entire axial length of the eye without the need for, for example, sutures to combine different measurements.

[0067] Figure 2 An example of a scanning pattern used in the measurement is shown, that is, it shows the position of the probe beam 28 in the xy plane during various A-scans. This type of pattern is described in EP 3021071. Other scanning patterns may also be used, such as those described in EP 3217144 or US 8705048.

[0068] A-scan analysis

[0069] Figure 3 This shows a single A-scan obtained by means of OCT analysis 28 (see Figure 4 The reflectance value of this single A-scan 28 (see Figure 4 The x = xi and y = yi positions are located in plane P at the vertex of cornea 36.

[0070] As those skilled in the art know, various structures of the eye generate different peaks in the reflectance values ​​corresponding to different depths z1, z2, z3... The first main peak at depth z1 may, for example, correspond to the anterior surface of the cornea 36, ​​the second peak at z2 corresponds to the anterior surface 40 of the lens 38, the next peak at z3 corresponds to the posterior surface 42 of the lens 38, and the last peak at z4 corresponds to the retina 44.

[0071] A-scans recorded in this manner can optionally be corrected for eye movements, for example, by using at least the following steps:

[0072] 1. Identify the reflection of at least one given eye structure (e.g., the anterior corneal surface) in an A-scan.

[0073] 2. Fit a model describing the shape and motion of the structure to the identified reflection location. For example, such a model could have geometric parameters of the structure (such as curvature) as well as motion parameters (such as three-dimensional position and velocity in x, y, and z coordinates).

[0074] Then, the parameters obtained in fitting step 2 can be used to convert the OCT measurements, specifically the incident coordinates xi,yi and the z coordinates obtained from the A-scan, into a frame-fixed coordinate system for the eye.

[0075] For example, suitable motion correction techniques are described in WO 2013 / 107649 or US 7452077.

[0076] These steps allow for the determination of the location of various structures in the eye, such as the cornea 36, ​​the anterior and / or posterior surfaces of the lens 38 40, 42 and / or the anterior surface of the iris 46, and the identification of their reflectance values.

[0077] Transmission Analysis

[0078] As mentioned above, the reflectance value of particular interest is the reflectance value ri corresponding to the reflection of the probe beam of A-scan i at retina 44.

[0079] This reflection value ri can be obtained, for example, through one of the following methods:

[0080] - Determine the maximum reflectance value in the region R surrounding the expected z-position of the retina;

[0081] - Integrate the reflectance values ​​over a given region R around the expected or determined z-position z4 of the retina (e.g., the z-position of the retina can be determined based on the z-position of the maximum reflectance value within the expected z-position range R of the retina).

[0082] - Fit a model of typical retinal reflection to the reflection values ​​at the expected z-position range R of the retina.

[0083] A more robust reflection value r'i can be obtained by combining the values ​​ri1, ri2, ..., rin of n A-scans i at points xi1 / yi1, xi2 / yi2, ..., xin / yin, with mutual distances less than a threshold d, such as d < 1 mm, < 0.5 mm, or < 0.25 mm, by means of, for example, calculating the average, median, or weighted average of ri, ri2, ..., rm.

[0084] The reflectance value ri obtained in this way is not only a function of retinal reflectivity, but also a function of the transmission of light from the eye along the path of the probe beam 28.

[0085] Therefore, if the eye includes scattering and / or absorption structures along the path of the probe beam 28, then the reflectance value ri decreases.

[0086] In a typical measurement, multiple A-scans i are performed, where i = 1...N (where N is at least 10, particularly at least 100, advantageously at least 1000). Figure 4 The probe beams 28 and 28' used for two such A-scans are shown.

[0087] Advantageously, the incident directions D of the probe beams outside the eye are parallel to each other and advantageously parallel to the visual axis A of the eye.

[0088] For parallel probe beams 28, 28' and eyes adapted to infinity, the probe beams will all strike the retina 44 at a common location 48 (if the incident direction of the external A-scan of the eye corresponds to the visual axis A of the eye, then it corresponds to the fovea).

[0089] Therefore, for these two A-scans, the difference in retinal reflectance values ​​ri is mainly due to the different transmission of the eye to the two probe beams 28 and 28'.

[0090] In other words, the reflectance value ri of the retina describes how the transmissivity of the eye changes as a function of the A-scan position xi,yi.

[0091] For example, if there are local scattering or absorption structures 50a-50f in the front of the eye, they can be detected and spatially resolved by examining the reflectance value ri as a function of the scanning position xi, yi (at least in the directions x and y, if not along z).

[0092] For example, these structures may include scattering or absorption structures 50a-50c at the posterior surface of the lens or scattering and / or absorption structures 50d-50f in the anterior half of the eye behind the lens.

[0093] This is Figure 5 The figure shows the reflectance value ri as a function of coordinates xi, yi for different eyes. Black or dark areas in the figure represent high reflectance values ​​ri, and white or bright areas represent low reflectance values ​​ri from the retina.

[0094] In each image, the pupil is easily identifiable. The location of the iris hit by the A-scan has a low reflectance value ri from the retina, and is therefore white.

[0095] Figure 5 The eye C shows a consistently high reflectance value ri from the retina within the pupil, indicating that the eye always has good transmittance.

[0096] Eyes A, B, and D show eyes with impaired transmission at certain locations xi,yi, indicating a defect in the anterior region of the eye.

[0097] It is important to note that this technique allows for the detection of not only scattering structures but also absorption structures. The latter is well-known to be difficult to detect by other methods.

[0098] PSF Analysis

[0099] Analyzing the reflectance value ri as a function of xi and yi allows for an estimate of the eye's PSF.

[0100] Related techniques are described, for example, in Goodman JW, “Introduction to Fourier optics”, 2nd edition (1996).

[0101] Specifically, and assuming that the lens and cornea of ​​the eye provide perfect imaging impaired only by defects 50a-50f in the anterior part of the eye, then the PSF can be calculated by the Fourier transform (FT) of the modulation transfer function (MTF) of the anterior eye, i.e.

[0102] PSF = FT(MTF) (1)

[0103] The modulation transfer function can be estimated from the reflection values ​​ri(xi, yi), as obtained by the measurements described in the "PSF Analysis" section above. Advantageously, the MTF is interpolated to a regular 2D grid, as this allows the use of an efficient FFT algorithm to perform the FT.

[0104] Specifically, and very closely related

[0105] PSF(u,v)=FT(ri(0xi,0yi)) (2)

[0106] Where θxi and θyi are the propagation angles of the probe beam used for A-scan i on the posterior side of the lens, and u and v are retinal coordinates. Angles θxi and θyi are measured along axis A of the eye.

[0107] Figure 6 It shows according to Figure 5 Examples of PSF(u,v) calculated from the reflectance values ​​ri(xi,yi) of the eyes. As can be seen, eye C, with its wide pupil and good uniform transmission, provides the best PSF, i.e., the PSF with the least scattering, while eyes A, B, and D have poorer imaging characteristics.

[0108] Figure 7 The profiles of PSF(u) and PSF(v) in the horizontal and vertical directions are shown, again targeting Figure 5 The eyes AD.

[0109] For quantitative analysis, the values ​​θxi,θyi can be calculated from xi,yi using the axial length L of the eye. In this context, this axial length L can be defined as the distance along axis A between the center of the lens 38 and the retina 44. Alternatively, for example, it can be defined as the distance along axis A between any other part of the lens 38 and the retina 44, or the distance between the vertex of the cornea 36 and the retina 44.

[0110] In particular, ray tracing techniques can be used to calculate the values ​​θxi and θyi.

[0111] By determining the position of the corresponding peak in the A-scan spectrum, this axial length L of the eye can be easily determined from an OCT A-scan. Figure 3 In the example, for instance, L is calculated based on z4–(z2+z3) / 2.

[0112] Therefore, this method advantageously includes the step of using the axial length L to estimate parameters describing the absolute dimensions of the PSF (such as the half-width of the PSF in the horizontal and / or vertical directions).

[0113] Furthermore, for quantitative analysis, it is necessary to know the absolute values ​​of xi and yi, for example, from one or more of the following sources:

[0114] - The scanning optics 24a and 24b can be calibrated to produce a known displacement relative to the axis of the system. In this case, the absolute values ​​of xi and yi can be derived from the settings of the scanning optics 24a and 24b for a given A-scan i.

[0115] - In OCT measurements, reflections from the iris can be identified, which allows the diameter d of the iris to be measured in coordinates xi,yi (see example). Figure 5 (C, Eye). This parameter can be compared with an image of the eye taken using a calibrated microscope, which allows the coordinates xi,yi to be transformed into absolute coordinates.

[0116] As an alternative to computing the Fourier transform of the dataset derived from ri(xi, yi), ray tracing can be used to determine at least one parameter of the eye, such as one or more parameters describing the eye's PSF.

[0117] For example, this ray tracing can be based on the following steps:

[0118] - Using OCT, the geometry of at least some of the refractive structures of the eye is measured. Advantageously, this includes measuring the geometry of the anterior and posterior surfaces of the cornea 36, ​​the anterior surface 40 of the lens, and the posterior surface 42 of the lens.

[0119] Using ray tracing, taking into account the geometry measured in the previous step, the intensity distribution at position 44 of the retina, resulting from the superposition of multiple ideal beams parallel to direction D, is calculated: In the ray tracing simulation, it can be assumed that the set of parallel and uniformly distributed beams covers the cornea of ​​the eye being tested. The refraction caused by the new beam axis at each optical interface (anterior and posterior cornea, anterior and posterior lens) is calculated using Snell's law and refractive indices known from the literature (e.g., Le Grand's eye model, values ​​of which can be found in Atchison DA and Smith G's "Optics of the Human Eye"). The trajectory of each beam through the eye until reaching the retina is calculated. If sufficient beams are used in this simulation, the density distribution of the points where these beams cross the retinal surface provides a good approximation of the eye's PSF for simulating the beam's incident axis.

[0120] For each simulated beam, a transmission value is determined based on one or more reflection values ​​*ri*, assuming that the reflection value *ri* is proportional to the transmittance at point *xi,yi*, and that *xi,yi* is located near the coordinates of the simulated beam (e.g., within 10 spot sizes). This transmission value *ri* (or the composite value *r'i*) can be used as a weighting factor for that particular simulated beam. The PSF generated by this simulation represents the optical imaging quality of the eye, including the effects of aberrations and obstacles (scattering and / or absorption).

[0121] The simulation can be further improved by taking into account the angle of incidence of each beam relative to the retina and weighting each beam according to the Stiles-Crawford effect (Stiles and Crawford 1933) (i.e., the angle dependence of retinal sensitivity).

[0122] For example, the techniques used to perform such ray tracing calculations are described in the following literature:

[0123] 1) Spencer G, Murty M, “General Ay-Tracing Procedure”, Journal of the Optical Society of America, Vol. 5, No. 6, p. 672 (1962), DOI: 10.1364 / JOSA.52.000672

[0124] 2) Einighammer J, “The Individual Virtual Eye”, Ttibingen University paper (2008), Chapter 3.2.3, http: / / hdl.handle.net / 10900 / 49149, and its references.

[0125] 3) Einighammer J et al., “The individual virtual eye: a computer model for advanced intraocular lens calculation”, J Optom 2009; 2:70-82, https: / / doi.org / 10.3921 / joptom.2009.70 and references.

[0126] For example, the eye's PSF can be used Figure 6 Alternatively, the graph shown in Figure 7 can be displayed directly to the operator. Alternatively, or in addition, the mathematical convolution of the PSF with a given image can be calculated and displayed to visualize how the eye perceives the given image.

[0127] notes

[0128] Advantageously, the A-scan used to measure the parameters includes multiple A-scans, advantageously at least 10 A-scans, particularly at least 100 A-scans, which are spaced at least 1 mm apart at the cornea, i.e., examining the macroscopic area of ​​the eye.

[0129] In particular, multiple A-scans are distributed across the entire pupil of the eye, allowing for the measurement of transmission across the entire pupil. The distribution can be uniform or irregular. Advantageously, it has a resolution of at least ten points in both the horizontal (i.e., along the x-axis) and vertical (along the y-axis).

[0130] In the above embodiments, the A-scans i all have the same incident direction, that is, they are parallel to direction D before entering the cornea, which is advantageously parallel to the optical axis or visual axis A of the eye.

[0131] In another embodiment, probe beams with different incident directions can be used.

[0132] For example, a first series of A-scans can be recorded with probe beams having mutually parallel incident directions along a first direction (e.g., D). Furthermore, multiple A-scans with probe beams having mutually parallel incident directions along a second direction (e.g., D) can be recorded. Figure 4 The second A-scan of the probe beams with mutually parallel incident directions (D') in the D'). For example, these measurements can be used for at least one of the following purposes:

[0133] - It can measure the PSF of the eye for different angles of incidence.

[0134] Information about the z-coordinate of a defect can be obtained by measuring how the structure shifts between two sets. Again, for example, ray tracing can be used to simulate the parallax effect between two sets being measured.

[0135] In yet another embodiment, the focal position of the probe beam can be varied during A-scan recording. For example, for a given position xi,yi, at least two A-scans with different focal positions can be recorded. Since the spatial resolution for defects 50a-50f is optimal at the focal plane of the probe beam, this allows, for example, measurements to be focused on a specific area of ​​the eye and / or more information about the z-position of a given defect.

[0136] This technique can be used with any type of OCT, especially for time-domain OCT and frequency-domain OCT. However, frequency-domain OCT, particularly swept-source OCT, has an advantage due to its ability to quickly obtain an A-scan.

[0137] While presently preferred embodiments of the invention have been shown and described, it should be clearly understood that the invention is not limited thereto, but may be practiced and implemented in other ways within the scope of the appended claims.

Claims

1. A method for measuring at least one parameter indicating the optical transmission quality of an eye, the method comprising the following steps: Record multiple optical coherence tomography (A-scan) scans for different corneal locations xi and yi of the eye. For each A-scan in the A-scan, the reflectance value ri at the retina of the eye is identified. One or more parameters are determined using the reflection value ri and the position xi, yi. The aforementioned multiple A-scans include a first multiple A-scan with mutually parallel incident directions (D) within 1°, such that the A-scans differ in their positions xi, yi, but not in the direction in which the beam irradiates the cornea of ​​the eye (30). The method further includes the following steps: By using the reflectance value ri to represent the reflectance value ri as an image in xi-yi-space, the location and spatial extent of at least one of the absorption and scattering structures in the anterior segment of the eye are determined.

2. The method of claim 1, wherein the parallel incident direction (D) is parallel to the visual axis (A) of the eye.

3. The method of claim 1 or 2, comprising a second multiple A-scan having mutually parallel incident directions (D'), wherein the incident direction (D) of the first multiple A-scan is different from the incident direction (D') of the second multiple A-scan.

4. The method of claim 1 or 2, wherein the multiple A-scans comprise multiple non-overlapping A-scans at the cornea (36) of the eye.

5. The method of claim 1 or 2, comprising the step of: focusing a probe beam for at least a portion of the A-scan onto the front of the eye.

6. The method of claim 1 or 2, comprising the step of: focusing a probe beam for at least a portion of the A-scan at a location between the posterior surface of the lens of the eye and the retina of the eye.

7. The method of claim 1 or 2, comprising the following steps: The focal position of the probe beam is changed while recording the multiple A-scans using the probe beam.

8. The method of claim 7, wherein for a given position xi, yi, at least two A-scans with different focal positions are recorded.

9. The method of claim 1 or 2, comprising the following steps: The reflection value ri is displayed as a function of the position xi, yi.

10. The method of claim 1 or 2, comprising the following steps: - Perform a Fourier transform on the dataset based on the reflection value ri, and - Derive the parameters from the results of the Fourier transform.

11. The method of claim 10, wherein the Fourier transform is a two-dimensional Fourier transform.

12. The method of claim 1 or 2, comprising at least one of the following steps: - The axial length (L) of the eye is determined from the A-scan using optical coherence tomography, and / or - The diameter (d) of the pupil is determined from the A-scan by means of optical coherence tomography.

13. The method of claim 12, comprising the following steps: - Perform a Fourier transform on the dataset based on the reflection value ri. - Derive the parameters from the results of the Fourier transform. - Use at least the axial length (L) and / or the diameter (d) to estimate the absolute size of the eye's point spread function.

14. The method of claim 1 or 2, comprising the following steps: The topology of at least one structure of the eye is determined from the A-scan.

15. The method of claim 14, wherein the at least one structure of the eye is selected from the group consisting of at least the cornea (36), the iris (46), the anterior surface (40) of the lens (38) and the posterior surface (42) of the lens (38).

16. The method of claim 14, comprising the following steps: The at least one parameter is determined using the reflection value ri and the topology of the structure in the ray tracing calculation.

17. The method of claim 1 or 2, wherein the optical coherence tomography is frequency domain OCT.

18. The method of claim 1 or 2, wherein the optical coherence tomography is a swept-frequency source OCT.

19. The method of claim 1 or 2, comprising the following steps: The reflection value ri is used to determine a one-dimensional or two-dimensional representation of the eye's point spread function.

20. An ophthalmic device, comprising - Optical coherence tomography interferometer (10-26), and - The control unit (32) is configured and adapted to perform the method as described in any one of claims 1 or 2.

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