SYSTEM AND METHOD FOR OBTAINING BIOMECHANICAL PARAMETERS OF OCULAR TISSUE THROUGH DEFORMATION OF THE OCULAR TISSUE

Abstract

A system for obtaining biomechanical parameters of ocular tissue includes an air-puff module to deliver an air-puff stimulus onto the ocular tissue, and an imaging device operatively coupled to the air-puff module.

The air-puff module includes a transparent window at its front with a transparent through hole for delivering the air-puff stimulus. The hole is aligned with an imaging device optical axis, such that the air-puff stimulus delivered onto the ocular tissue can be centred on an apex of the ocular tissue and made collinear with the optical axis. The transparent window and through hole allow continuity of imaging of the ocular surface.

The imaging device captures the 3D coordinates of points distributed on an ocular tissue surface in groups of simultaneous points.

The system includes a component for selecting and changing location and distribution of captured points on the ocular tissue, and a processing component to process the points.

Claims

1. A system for obtaining biomechanical parameters of ocular tissue, the system comprising: an air-puff module configured to deliver at least one air-puff stimulus onto the ocular tissue; an imaging device operatively coupled to the air-puff module; wherein the air-puff module comprises a transparent window at its front thereof, the transparent window having a transparent through hole for delivering the at least one air-puff stimulus, the hole configured to be aligned with an optical axis of the imaging device, such that the air-puff stimulus delivered onto the ocular tissue is configured to be centered on an apex of the ocular tissue and is configured to be made collinear with the optical axis, the transparent window and its transparent through hole further allowing continuity of imaging of the ocular surface; the imaging device being configured to capture the three-dimensional coordinates of a plurality of points distributed on a surface of the ocular tissue, captured in groups of at least two simultaneous points; the system further comprising: means configured for selecting and changing the location and distribution of the plurality of captured points on a surface of the ocular tissue; and processing means configured to process the plurality of points provided by the imaging device for obtaining biomechanical parameters of the ocular tissue.

2. The system of claim 1, wherein the imaging device comprises means configured to generate one or several optical beams, configured to go through the transparent window and its transparent through hole and be directed to the ocular tissue.

3. The system of claim 2, further including at least two optical beams having orthogonal polarization states.

4. The system of claim 1, wherein the imaging device comprises means for laterally scanning one or several optical beams across the ocular tissue.

5. The system of claim 4, wherein the means for laterally scanning is a beam shifting or steering device.

6. The system of claims 1, wherein the air-puff module comprises an optical window at a rear part of the air-puff module, and the air-puff module is integrated into an optical path of the imaging device by aligning the centeres and optical axes of the optical window and the imaging device.

7. The system of claims 1, wherein the air-puff module is integrated into an optical path of the imaging device by using a sample arm objective lens of the imaging device as an integral part of a rear part of the air-puff module.

8. The system of claim 1, wherein the system further comprises a micro lenslet array integrated in the air-puff module.

9. The system of claim 8, wherein the back end of the micro lenslet array is configured to serve as a partial reflector for a common-path configuration in optical coherence tomography.

10. The system of claim 1, wherein the imaging device is an optical coherence tomography apparatus.

11. A method for obtaining biomechanical parameters of ocular tissue through deformation of the ocular tissue, the method including the following steps: generating an air stimulus for delivery onto the ocular tissue delivering the air stimulus through a transparent through hole of a transparent window; selecting the location and distribution of the plurality of points to capture on a surface of the ocular tissue, capturing three-dimensional coordinates of a plurality of points distributed on a surface of the ocular tissue, captured in groups of at least two simultaneous points, and processing the three-dimensional coordinates of the plurality of captured points to obtain biometrical parameters of the ocular tissue.

12. The method of claim 11, wherein the processing means are configured to obtain a biomarker of the ocular tissue by analysing asymmetries in deformation provided by the imaging device at opposing points.

13. The method of claim 11, wherein the processing means are configured to carry out finite-element-model based calculation for reconstructing biomechanical properties of the ocular tissue.

14. The method of claim 11, wherein the method is carried out with a system comprising: an air-puff module configured to deliver at least one air-puff stimulus onto the ocular tissue; an imaging device operatively coupled to the air-puff module; wherein the air-puff module comprises a transparent window at its front thereof, the transparent window having a transparent through hole for delivering the at least one air-puff stimulus, the hole configured to be aligned with an optical axis of the imaging device, such that the air-puff stimulus delivered onto the ocular tissue is configured to be centered on an apex of the ocular tissue and is configured to be made collinear with the optical axis, the transparent window and its transparent through hole further allowing continuity of imaging of the ocular surface; the imaging device being configured to capture the three-dimensional coordinates of a plurality of points distributed on a surface of the ocular tissue, captured in groups of at least two simultaneous points; means for selecting and changing the location and distribution of the plurality of captured points on a surface of the ocular tissue; and processing means configured to process the plurality of points provided by the imaging device for obtaining biomechanical parameters of the ocular tissue.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] To complete the description and in order to provide a better understanding of the disclosure, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the disclosure, which should not be interpreted as restricting the scope of the disclosure, but just as an example of how the disclosure can be carried out. The drawings comprise the following figures:

[0062] FIG. 1 shows a schematic view of the system components according to a possible embodiment of the system of the disclosure.

[0063] FIG. 2 shows two possible scanning patterns used in the system of FIG. 1.

[0064] FIGS. 3-5 show different ways of carrying out the lens-mirror structure shown in FIG. 1, using a multi beamlets configuration.

[0065] FIG. 6 shows another way of carrying out the lens-mirror structure shown in FIG. 1, according to another possible embodiment of the disclosure.

[0066] FIG. 7 shows a schematic view of another embodiment of the system of the disclosure.

[0067] FIG. 8 shows the nine points wherein OCT imaging is conducted in the system of Fig.7.

[0068] FIG. 9 shows a schematic representation of part of still another possible embodiment of the disclosure.

[0069] FIG. 10 shows the results of the spatial and temporal pressure profile characterization, for different solenoid voltages.

[0070] FIG. 11 shows the results of the spatial and temporal pressure profile characterization, for different distances to the cornea.

[0071] FIG. 12 shows the displaced area over time for an ex vivo porcine eye under varying controlled IOP.

[0072] FIGS. 13-15 show some results of the deformation asymmetries obtained with the present disclosure.

DETAILED DESCRIPTION OF THE DRAWINGS

[0073] The following description is not to be taken in a limiting sense but is given solely for the purpose of describing the broad principles of the disclosure. Embodiments of the disclosure will be described by way of example, with reference to the above-mentioned drawings.

[0074] FIG. 1 shows a schematic view of the system components according to a possible embodiment of the system of the disclosure, showing the swept-source OCT system 100 coupled with an air-puff module 200 for inducing corneal deformation. Typically, the swept-source OCT 100 comprises a wavelength-swept laser source SS, a dual balanced photodetector DBP, a reference arm mirror RM, a galvanometer mirror pair GM and an objective lens L. Different ways of carrying out this lens-mirror structure are shown in FIGS. 3-6.

[0075] The air-puff module 200 includes a repurposed industry-standard, non-contact tonometer air-puff unit. The air-puff unit is based on a piston Pi with a plenum chamber PI and is driven by a rotary solenoid RS. The plenum chamber PI has front and rear windows, PW and OW, respectively. The air-puff module 200 is coupled to the swept-source OCT 100 via the optical window OW at the back of the plenum chamber PL. The front window PW is a transparent methacrylate window fitted to the front of the plenum chamber having a thickness of 5 mm in the axial direction. The transparent window (made of methacrylate in this specific example, but it can be made of any other transparent material) has a centered 2.4 mm wide hole—also transparent—which acts as the air-puff outlet (outlet diameter OD), which provides an unobstructed ssOCT field of view. OA represents the optical axis of the system. Any window thickness ranging from 0.5 mm to 10 mm and hole diameter from 0.5 mm to 5 mm is appropriate for delivery of an air-puff. The transparent window thickness and transparent through-hole diameter affect the spatial-temporal profile of the air-puff.

[0076] The air-puff unit is connected to custom-designed circuitry to provide a controlled voltage to the rotary solenoid for varying the puff pressure and duration (DC: 48 V, 2 A DC power supply, R: Power resistor, S: switch).

[0077] The air-puff can be directed to a cornea C (cf. FIG. 1) at a specific but variable eye distance ED. PS represents the pressure sensor plane.

[0078] The cornea C is a model cornea made of soft, hydrophilic contact lens materials mounted in a plastic artificial eye chamber, filled in with saline solution, and pressurized by a water column system to model the intraocular pressure (IOP). This model eye is constructed for validation purposes.

[0079] In the present embodiment, the air-puff module 200 provides a minimum air-puff FWHM duration of ˜11 ms, reaching a maximum pressure on the corneal apex of ˜13 kPa and impacting over a FWHM diameter of 3.34 mm, for a distance to the eye of 11 mm.

[0080] The custom-designed ssOCT 100 includes a 200 kHz 1300 nm VCSEL swept-source (Thorlabs, USA), with an axial resolution of 16 μm. The ssOCT also has galvanometric scanning mirrors GM (ScannerMAX, USA) with very-small-diameter moving magnets, along with special bearing materials, providing an exceptionally high acceleration and RMS duty cycle and a 7.5 kHz small angle bandwidth for rapid linear, repeatable scans.

[0081] These allowed to implement two scan patterns over a lateral range of 15 mm in all scan directions at a pattern repetition frequency of 1 kHz. The first pattern was a cross-meridian scan (cf. top image of FIG. 2), while the second comprised of three horizontal lines, separated by 2 mm each, above and below the central meridian (cf. bottom image of FIG. 2). A scan pattern repetition frequency from 1/1000 of the laser scan frequency to the laser scan frequency is suitable for measurement or corneal deformation taking place on the millisecond scale, and certainly before the blink-reflex takes place. Fan (field)-distortion correction algorithms were applied to measure true deformation geometry. Registration of the optically-displaced corneal apex area and subsequent segmentation routines on the spatial-temporal corneal deformation profiles along the different meridians were applied. Metrics of asymmetry of deformation were considered for differentiating healthy and “abnormal” corneal deformation profiles.

[0082] By controlling the piston thrust in the cylinder, it is possible to control the output of the air-puff pressure and its duration. Also, by changing the distance of the air-puff module to the eye, it is possible to control the air-puff impact area.

[0083] FIGS. 8-9 show a schematic representation of another embodiment of the system of the disclosure, also comprising multi beamlets configuration with a galvanometric mirror GM′ and a scan lens SL. This embodiment is capable of simultaneously scanning several parallel meridians (see different parallel meridians 10a and 10b in FIGS. 8 and 9, respectively) at an arbitrary angle orientation with a single scanner, by means of depth encoded multiplexing.

[0084] FIG. 10 shows another possible embodiment, also comprising a multi beamlets configurations. In this case a galvanometric mirror pair GM″ is used for producing a scanning pair. This embodiment is capable of simultaneously scanning several concentric circles to monitor corneal deformation.

[0085] FIG. 11 shows a part of another embodiment of the disclosure, capable of scanning at two meridians simultaneously at an arbitrary angle orientation with only one single scanner, by means of depth encoded polarization multiplexing.

[0086] This system outlined in this FIG. 11 works in the following way:

[0087] Scanning at both meridians is realized with a common scanning mechanism (2D or 3D in general): [0088] The same scanner (scanners pair) is used for both meridians. [0089] Scanned pattern can be freely rotated (over system optical axis) with image rotators. [0090] The resulting scan pattern at the sample provides simultaneous scanning with mutual angle between 2D or 3D patterns between 0-90 degrees.

[0091] The images rotation can be realized with: [0092] A dove prism (additional polarization components are required to compensate polarization change due to Dove prism rotation) [0093] A K-mirror that should be free or with minimal influence of effects describer for Dove prism.

[0094] Polarization depth encoded multiplexing is realized via: [0095] A glass plate introduced to arm of one polarization channels (depth difference on OCT image is given by glass plate thickness and refractive index−d*n) [0096] Appropriate section of PM fiber two introduce delay between orthogonal polarization states.

[0097] For the corneal tomography: one channel set to fixed orientation (e.g horizontal or vertical) and can work as reference; the other channel uses continuous rotation to provide 3D tomographic scan of the cornea (Pentacam like). Optionally both channels set initially in orthogonal mode are rotated by 45° toward each other to provide fast 3D scanning mode.

[0098] FIG. 7 shows a schematic view of another embodiment of the system of the present disclosure.

[0099] This embodiment is a low-cost system for screening corneal biomechanics-related pathologies. As it is explained below in detail, it uses an inexpensive custom built swept-laser source, which is connected to a fiberized coupling system to deliver the multitude of deformation probing light beams to the cornea. Customized opto-mechanics and optics were built in a first prototype, integrating a tonometer-like air-puff device and a standardised cornea-mimicking sample for validation purposes.

[0100] This embodiment provides a low-cost keratoconus-biomarker screening system by proposing a device with 9-corneal monitoring points using a swept-source OCT coupled with an air-puff module 200. The air-puff 200 can be the same as in the previous embodiment.

[0101] As with the previous embodiment, the main idea behind this low-cost screening system is the use of Optical Coherence Tomography (OCT) imaging of a subject's corneal deformation induced by a tonometer-like air puff device. OCT imaging is conducted at a multitude of points arranged circularly around the corneal apex, and at the corneal apex itself (as shown by the 9 points in FIG. 8). Asymmetries in the deformation profiles at opposing points provide a biomarker of corneal mechanical anomalies.

[0102] To keep the cost down, no scanning apparatus is used, whilst the deformation signal from reflections coming from 9 corneal points is recorded all in the same motion-mode (M-mode) axial scan, via depth multiplexing.

[0103] A low-cost short-cavity Fabry-Perot swept laser 100′ is used as OCT imager and is intended for depth multiplexing the corneal deformation signal returning from nine corneal points (see FIG. 8).

[0104] The wavelength tuning range as a function of the laser sweep (repetition) rate (A-scan rate) was ˜8 nm, for a 5 kHz A-scan rate; and ˜15 nm for a 2.5 kHz A-scan rate. The last option is preferred as the right compromise between OCT axial resolution and dynamic deformation sampling capabilities.

[0105] The system further comprises a 1×9 fibre coupler, which is built by cascading one and three 1×3 couplers. FIG. 6 schematically shows the 1×9 coupler. The sample arm design requires nine focused beams to be arranged around the model cornea with their focal spot landing in and around the corneal anterior surface. Sample arm optics, including nine fibre collimators, nine focusing lenses and a conical mirror 300 were required to attain such design, as schematically shown in FIG. 7. A specific optomechanical mount was designed to hold these components together, which is schematically represented as a ring 310 in FIG. 7. It is possible to use a more complex mount, which allows to change the radius of the circularly arranged spots, by sliding in and out the conical mirror 310; and also a more compact one, made out of micro lenslet array 400, with each lenslet mounted on a custom spacer of set thickness, meant for multiplexed pathlength testing (as shown in FIG. 9, explained below).

[0106] A Labview program was used to synchronise the air-puff ejection with the recording of the M-mode spectra coming from the model cornea, using the benchmarking OCT system connected with the low-cost swept source. A programmable digitizer was used to record the spectra. The Labview program was used to resample the spectra k-linear and provide an M-mode view of the model cornea deformation.

[0107] As previously outlined above, FIG. 9 shows another embodiment of a multi beamlets mechanism to provide multi-spot illumination of the cornea C from single gaussian input beam (preferably, a collimated beam) and a micro lenslet array 400. This provides a more compact solution. The transparent frontal window PW with its air-puff outlet OD is also schematically shown in this FIG. 9.

[0108] Each spatial channel has a dedicated focusing element: micro-hemi-spheres of the micro lenslet array 400; 3D printed spherical surfaces; phase mask. The system further includes an element to introduce multichannel depth encoded multiplexing. Each channel has a spacer between base plate and focusing element providing different optical path difference between each channel and reference beam. The rear part (from the side of input beam) of the base plate can be partially mirror-coated to support common path imaging mode.

[0109] Different air-puff pressures, durations and distances to the eye were analysed, for optimization of the air-puff module 100, as shown in the following Figures.

[0110] FIG. 10 shows the air-puff pressure profile on apex at an eye distance ED of 11 mm, for two different solenoid voltages, with a 5-ohm series resistor (and with a 33-ohm series resistor (flatter profile).

[0111] FIG. 11 shows the air-puff pressure profile on apex using a 5-ohm series resistor, for three eye distances: 8 mm (uppermost curve), 11 mm (middle curve) and 13 mm (lowermost curve).

[0112] FIG. 12 shows the reduction of the displaced cross-meridian area over time, from a maximum of ˜4.3 to 1.8 mm.sup.2, with increasing intraocular pressure, IOP, from 15 to 30 mm Hg for an ex vivo porcine eye.

[0113] With the system of the present disclosure, it is possible to detect comeal deformation profiles and deformation asymmetries that are useful for corneal biomechanics diagnostics and pathology screening, as shown in FIGS. 13-15.

[0114] FIG. 13 is an overlay of the OCT images on two meridians at maximum deformation before and after localized corneal softening treatment, to show the effectiveness of the instrument in picking up the asymmetric deformation, visible only in the vertical meridian after treatment.

[0115] FIG. 14 represents the segmented anterior corneal surfaces on the horizontal and vertical meridians overlaid at maximum deformation to appreciate the asymmetry.

[0116] FIG. 15 represents the evolution vs time of the asymmetry in a displaced area.

[0117] In this text, the term “comprises” and its derivations (such as “comprising”, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.

[0118] On the other hand, the disclosure is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the disclosure as defined in the claims.