WO2024251604A1 - Method with high measurement sensitivity for optical biometrics on eyes with cataract disease - Google Patents

Abstract

The invention relates to a method for optical biometrics carried out in particular on eyes with a cataract disease. The method is based on a method of optical coherence tomography in which measuring beams are generated not only along the visual axis of the patient's eye, but also with a lateral shift relative to the visual axis in order to obtain usable measurement data with potentially improved transmission through the cataract-infected eye. The proposed method for optical biometrics carried out on eyes with cataract disease is based on an interferometric OCT system without an active scanner or wobble device, in which, in addition to the A-scan along the visual axis, laterally offset A-scans with a high repetition rate are carried out. This method makes it possible to collect biometric measurement data even for eyes with cataract disease. As the method does not require a technical scanner or wobble device, it is very simple and inexpensive to implement.

Description

Method with high measurement sensitivity for optical biometry of eyes with cataract disease

The present invention relates to a method for optical biometry, particularly of eyes with cataract disease. The method is based on an optical coherence tomography (OCT) method, in which measuring beams are shifted not only along the visual axis of the patient's eye, but also laterally to the visual axis in order to obtain usable measurement data with a possibly better transmission of the cataract-affected eye.

A cataract, also known as a cataract, lens cataract or lens opacity, is a clouding of the lens of the eye. If you look at people who have an advanced cataract, you can see the gray color behind the pupil, which is where the term "cataract" comes from. In most cases, the clouded lens can be surgically replaced with an artificial lens implant.

Cataract surgery to remove the clouded natural lens of the eye and implant an artificial lens (intraocular lens - IOL) represents a cost of approximately 25-30 million.

With 10,000 procedures per year, it is the most frequently performed operation on the human body worldwide.

Before cataract surgery, it is essential to measure the biometry of the cataract eye in order to be able to calculate the individually appropriate optical refractive power of the IOL and to achieve an eye that is as right-sighted as possible, i.e. emmetropic, after the procedure.

However, optical biometry requires optical media that allow a certain minimum transmission, which may not be the case, especially in eyes with completely opaque cataracts. According to the known state of the art, numerous solutions are known that deal with measuring the biometrics of eyes with cataracts.

Since the introduction of the lOLMaster by ZEISS in 1999, optical biometers for measuring eyes with cataracts have largely replaced the measurement of eye length using ultrasound methods, as these can collect measurement data without contact with the eye and are also more accurate. However, optical methods require sufficient transmission of the measuring beam through the clouded lens of the eye in order to be able to collect measurement data at all.

By using modern OCT biometers, which are based on a so-called “swept source” with a measurement sensitivity of approx. 100 dB, it is possible to perform biometric measurements on approx. 95% of cataract patients.

As described in the brochure [1] of the lOLMaster 700 from ZEISS, modern biometers use not only the sensitive interferometric measuring method in the so-called A-scan (measurement of the position of the optical surfaces in the eye along the visual axis) but also scanners for the lateral deflection of the OCT measuring beam for imaging biometry in the so-called B-scan (azimuthal cross-sectional images of the optical surfaces in the eye).

These B-scans can measure the optical surfaces (and other optically scattering structures) in the eye at any azimuthal angle within the opening of the pupil using, for example, an x-y galvanometer scanner system. This also makes it possible to capture the optical interfaces in the case of locally dense cataracts in the opening of the pupil despite these local image losses. Consequently, lateral scanning also makes a significant contribution to increasing the measurement sensitivity in the case of very dense cataracts in optical biometry.

However, the increasing costs for optical biometers due to additional optical scanner systems are a disadvantage. In particular, it must be taken into account that that ultrasound biometers are available on the market at a much lower cost than optical biometers and can also measure very dense cataracts without any problems.

JP 6198675 B2 describes an ophthalmological device that is able to scan light reflected from a patient's eye without using a galvanometer mirror. The ophthalmological device comprises a light source and an optical system that guides the light from the light source to a patient's eye. The optical system contains a lens that has a lens drive mechanism to move the lens within an orthogonal plane perpendicular to the light axis. The irradiation position and/or irradiation angle can thus be changed for the light generated by the light source and emitted to the subject's eye.

With the solution approach described here using an electromagnetic (so-called) wobble device, it is possible to generate additional, laterally offset A-scans using U- or V-shaped scanning patterns in order to obtain measurement data for eyes with very dense cataracts. However, this still requires additional technical effort for optical biometers.

Among other things, a solution to motivate active re-fixation of patients in an optical biometer was already investigated in the master dissertation “Detection of Purkinje Images for Automatic Positioning of Fixation Target and Interferometric Measurements of Anterior Eye Chamber” by Mariana Q. D. R. Almeida [2].

The focus was on the detection of Purkinje reflections of the lens interfaces of the patient's eye, which are essential for a biometric measurement of the lens distances using a less sensitive "time domain" method of partial coherence interferometry (with approx. 80 dB). Spiral patterns and parts of spiral patterns were used as fixation targets to activate the refixation of a patient's eye to be measured. However, the use of such dynamic 2D fixation targets for improved penetration of inhomogeneous dense cataracts was not reported.

Literature:

[1 ] DE_32_010_0009ll; printed in Germany: CZ-l/2015; www.zeiss.com/iolmaster700

[2] Master's dissertation; Integrated Master on Biomedical Engineering; “Detection of Purkinje Images for Automatic Positioning of Fixation Target and Interferometric Measurements of Anterior Eye Chamber”; Mariana Quelhas Dias Rodrigues Almeida (student number 23279); Winter semester 2011/12 20th of April, 2012 Universidade Nova de Lisboa, Faculdade de Ciencias e Tecnologia

[3] Scott M. McRae et al; “Customized Corneal Ablation and Super Vision”; Journal of Refractive Surgery, 2013;16(2):S230-S235; ttps://doi. org/10.3928/1081-597X-20000302-06

[4] Christoph K. Hitzenberger; “Optical Measurement of the Axial Eye Length by Laser Doppler Interferometry”; Investigative Ophthalmology & Visual Science; Vol. 32, No. 3, March 1991

The present invention is based on the task of providing a method for optical biometry with which measurement data can also be obtained for eyes with cataract disease. The device to be used for the optical biometry method should be cost-effective and preferably should not require a technical scanner or wobble device. In particular, the OCT measuring beam should not only be used on the visual axis of the patient's eye with strict fixation of the patient, but also for Measuring apertures shifted laterally to the visual axis, with possibly better transmission through the optically inhomogeneous cataract.

According to the invention, the object is achieved by the features of the independent claims. Preferred developments and embodiments are the subject of the dependent claims.

The present task is solved with the proposed method for optical biometry of eyes with cataract disease, based on an interferometric OCT system without active scanner or wobble device, characterized in that in addition to the A-scan along the visual axis, A-scans offset laterally to this are realized with a high repetition rate.

According to the invention, the fixation restlessness of the patient's eye is exploited over a longer measurement period. By evaluating a large number of A-scans, a measurement value for an intraocular distance of each boundary surface of the eye is determined and output.

According to the invention, the object is achieved by the features of the independent claims. Preferred developments and embodiments are the subject of the dependent claims.

A first group of advantageous embodiments relates to the longer measuring time, which is in the range of 5s to 30s, preferably up to 60s and particularly preferably up to 200s or even longer.

A second group of advantageous embodiments relates to the determination of the distance and/or the direction of the A-scans offset laterally to the visual axis. This is preferably carried out by detecting the 1st Purkinje reflex or the reflex of an external light source from an image of the eye. A third group of advantageous embodiments concerns the verification of whether a sufficiently large eye movement is ensured within the fixation restlessness of the patient's eye. In particular, from the large number of A-scans, only those whose detected direction or whose detected distance from the visual axis is not too large are taken into account in the evaluation.

A fourth group of advantageous embodiments concerns the assessment of the quality of the measured values. In particular, it is checked that, in the large number of A-scans, there are individual A-scans whose detected direction or whose detected distance lies within a tolerance to the visual axis.

A final group of advantageous embodiments relates to the measurement method itself. The measurements of the plurality of A-scans within the longer measurement time run automatically as soon as the measurements are activated, whereby no change in the position and/or direction of the fixation light occurs during the measurements of the plurality of A-scans.

The present method, based on optical coherence tomography, is used to measure distances in an eye suffering from cataracts in order to select the IOL to be implanted with the appropriate refractive power. Although the method is intended in particular for measurements in eyes already suffering from cataracts, it can in principle be used for measurements in all eyes, e.g. eyes with an IOL already implanted, silicone-filled eyes, aphakic eyes and phakic eyes without cataracts.

The invention is described in more detail below using exemplary embodiments.

The proposed method based on an interferometric OCT system without active scanner or wobble device with high measurement sensitivity for optical biometry of eyes with cataract disease, in addition to the A-scan along the visual axis, A-scans offset laterally to this are realized with a high repetition rate.

According to the invention, the fixation restlessness of the patient's eye is exploited within a longer measuring time, a large number of A-scans are evaluated and only one measured value is output for an intraocular distance of each boundary surface of the eye.

In particular, the invention provides for the natural fixation restlessness of the patient's eye to be exploited during longer measurement times with high A-scan repetition rates. This is intended to ensure that, in addition to the A-scan in the visual axis with a possible optical impenetrability, further laterally offset but measurable A-scans of the patient's eye can be recorded.

It is known from the scientific article [3] by Scott M. McRae et al. that the human eye moves around a fixation target in a range of typically 0.5 to 2 mm in horizontal and vertical direction within a period of up to about 30 seconds.

This self-movement should be used to realize A-scans at different points on the eye lens during longer measurement times. It is known from the application of eye trackers that after about 30 - 60 s these eye movements become even larger.

Since these rather sporadic and statistical "B-scans" do not reveal any lateral positions that can be strictly assigned to each A-scan in scanner systems, the method according to the invention will yield a large number of measurement data (or will not yield them at optically dense locations in the cataract lens), which must be organized in particular to determine the eye length and also to determine the other axial lengths in the eye, such as the corneal thickness, the anterior chamber depth and the lens thickness. According to the invention, criteria are derived based on the known general anatomy and geometry of the position of the optical surfaces of the eye of interest, implemented in algorithms and the plausible biometric data with tolerances evaluated immediately after the measurement using a computer and entered into the biometer for further use. The lateral position of the respective A-scan can be determined by additional detection of the 1st Purkinje reflex in the image of the eye.

In his specialist article [4], Christoph K. Hitzenberger documented the results of his investigations comparing the accuracy and reproducibility of measuring the geometric eye length using laser interferometry and ultrasound technology. It was found that laser interferometry (LDI) based on Doppler technology in combination with partially coherent light achieves high accuracy, high transverse resolution and greater comfort for the patient.

Furthermore, it was found that with a lateral offset of +/- 10° when measuring the eye length to the visual axis, only a measurement error of approximately 100pm occurs, which is acceptable for general biometric application in severe cataracts and is therefore comparable to ultrasound measurements in terms of measurement errors.

For the proposed method, the use of a fixation mark is advantageous in order to motivate a change in the direction of gaze of the eye to be measured. In addition to a simple fixation light, changing two-dimensional patterns or images can also be used for this purpose.

Furthermore, an existing headrest can be designed to allow slight lateral movements or rotational movements of the patient's head. According to a first advantageous embodiment, the longer measuring time is in the range of 5s to 30s, preferably up to 60s and particularly preferably up to 200s or even longer.

As already described, in addition to the A-scan along the visual axis, A-scans offset laterally to it are carried out at a high repetition rate. According to the invention, the distance and/or the direction of the A-scans offset laterally to the visual axis are determined. This is preferably carried out according to a second advantageous embodiment by detecting the 1st Purkinje reflex from an image of the eye.

However, it is also possible to determine the distance and/or direction of the A-scans offset laterally to the visual axis by detecting controlled reflections of an external light source from an image of the eye.

For the function of the method according to the invention, it is imperative to check whether a sufficiently large eye movement is guaranteed for the patient's eye within the fixation restlessness.

According to a third advantageous embodiment, from the large number of A-scans, only those whose detected direction or whose detected distance from the visual axis is not too large are taken into account in the evaluation.

According to the invention, only A-scans whose detected direction deviates by <10° or whose detected distance deviates by <2mm from the visual axis should be taken into account in the evaluation.

It is also advantageous if it is ensured that, among the large number of A-scans, there are individual A-scans whose detected direction or distance lies within a tolerance to the visual axis. This allows the quality of the measured values to be assessed. For this purpose, among the large number of A-scans, there should be at least one A-scan, preferably more than 5, whose detected direction deviates from the visual axis by >2.5° or whose detected distance deviates from the visual axis by >0.5 mm. This inevitably also ensures that there is a sufficiently large eye movement within the fixation restlessness of the patient's eye.

According to the invention, the measurements are repeated with the predetermined measuring time until at least 1, preferably 5 measured values are available whose detected direction deviates between 0° and 10° or whose detected distance deviates between 0mm and 2mm from the visual axis.

However, it is also possible to choose the time duration for the measurements so long that this condition is fulfilled.

According to a particularly advantageous embodiment, the measurements of the plurality of A-scans run automatically within the longer measurement time as soon as the measurements are activated once. Preferably, there is no change in the position and/or direction of the fixation light during the measurements of the plurality of A-scans.

The solution according to the invention provides a method for optical biometry, particularly of eyes, which is particularly suitable for eyes with cataracts. The method is based on an optical coherence tomography method in which measuring beams are shifted not only along the visual axis of the patient's eye, but also laterally to the visual axis in order to obtain usable measurement data with a possibly better transmission of the cataract-affected eye. The device used for the optical biometrics procedure is cost-effective and does not require a technical scanner or wobble device.

The present method, based on optical coherence tomography, is used to measure distances in an eye suffering from cataracts in order to select the IOL to be implanted with the appropriate refractive power. Although the method is intended in particular for measurements in eyes already suffering from cataracts, it can in principle be used for measurements in all eyes, e.g. eyes with an IOL already implanted, silicone-filled eyes, aphakic eyes and phakic eyes without cataracts.

Claims

patent claims 1. Method with high measurement sensitivity for optical biometry of eyes with cataract disease, in which, based on an interferometric OCT system without active scanner or wobble device, in addition to the A-scan along the visual axis, A-scans offset laterally to this are realized with a high repetition rate, characterized in that for this purpose the fixation restlessness of the patient's eye is exploited within a longer measurement time, that a large number of A-scans are evaluated and that in each case a measurement value is output for an intraocular distance of each boundary surface of the eye. 2. Method according to claim 1, characterized in that the longer measuring time is in the range of 5s to 30s, preferably up to 60s and particularly preferably up to 200s or even longer. 3. Method according to claim 1, characterized in that the distance and/or the direction of the A-scans offset laterally to the visual axis is determined by detecting the 1st Purkinje reflex from an image of the eye. 4. Method according to claim 1, characterized in that the distance and/or the direction of the A-scans offset laterally to the visual axis is determined by detecting controlled reflections of an external light source from an image of the eye. 5. Method according to claim 1, characterized in that from the plurality of A-scans only those are taken into account in the evaluation whose detected direction deviates by <10° or whose detected distance deviates by <2mm from the visual axis. 6. Method according to claim 1, characterized in that in the plurality of A-scans at least one A-scan, preferably more than 5, is present is/are whose detected direction deviates from the visual axis by >2.5° or whose detected distance deviates by >0.5 mm in order to check whether a sufficiently large eye movement is ensured within the fixation restlessness of the patient's eye. 7. Method according to claim 1, characterized in that the measurements are repeated with the predetermined measuring time until at least 1, preferably 5 measured values are present whose detected direction deviates between 0° and 10° or whose detected distance deviates between 0mm and 2mm from the visual axis. 8. Method according to claim 1, characterized in that the time duration for the measurements is chosen to be long enough that at least 1, preferably 5 measured values were obtained whose detected direction deviates between 0° and 10° or whose detected distance deviates between 0mm and 2mm from the visual axis. 9. The method according to claim 1, characterized in that the measurements of the plurality of A-scans within the longer measuring time are carried out automatically as soon as the measurements are activated. 10. Method according to claim 1, characterized in that the measurements of the plurality of A-scans are carried out without changing the position and/or direction of the fixation light.