TOMOGRAPHY

ACKNOWLEDGEMENT This invention was made with government support under grant EY027759 awarded by the National Institutes of Health. The government has certain rights in this invention.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority upon U.S. provisional application Serial No. 62/924,384 filed on October 22, 2019. This application is hereby incorporated by reference in its entirety.

BACKGROUND

Optical coherence tomography (OCT) is widely used in ophthalmology research and clinical practice. OCT images are affected by different factors that result in nonlinear image distortions, which can affect the 3D interpretation of these images. Currently, no commercial OCT device provides anatomically correct (undistorted) OCT images. Approaches based on optical models have been used successfully to correct for complex optical distortions, but these approaches are not directly translatable to commercial OCT devices as their optical details are proprietary and cannot be disclosed. Further, current approaches lack details about critical imaging parameters (e.g. distance between OCT camera and the eye).

Posterior segment OCT has become a critical tool for retinal and optic nerve head (ONH) imaging. Accurate imaging is critical for both clinical diagnosis as well as research. An inherent limitation of posterior segment OCT is nonlinear image distortions, limiting most OCT-based diagnostic to changes in tissue thickness (thickness measurements in the direction the imaging rays are theoretically not impacted by these distortions). However, recent animal research proposes that 3D morphological changes at the ONH are promising biomarkers for early glaucoma diagnosis.

Glaucoma is the second leading cause of blindness in the world and early diagnosis is critical for best treatment success. Glaucoma specialists examine the thickness of the retinal nerve fiber layer on OCT to diagnose glaucoma and track its progression. As this thickness measure is in the optical path, it is less affected by distortions. It has been recognized that there are 3D pathologic changes in the ONH (i.e. cupping of the lamina cribrosa) that are indicative of the disease. These changes occur both within and across the optical axis, thus are highly affected by the distortions.

Anatomically correct (undistorted) OCT images are needed to establish new biomarkers based on 3D morphological features. Currently, no commercial OCT device provides anatomically correct (undistorted) OCT images.

SUMMARY

Disclosed herein are methods for removing nonlinear distortions from images of the eye generated optical coherence tomography (OCT) devices. In one aspect, the methods involve applying reference markers of known dimensions to the eye and/or using inherent anatomical features and a second imaging modality to quantify one or more additional reference markers. The methods disclosed herein can be performed with data from any commercial or experimental OCT device without modifying the device. Furthermore, the methods disclosed herein can provide information useful for diagnosis of diseases of the eye such as, for example, glaucoma.

The advantages to the invention will be set forth in part in the description that follows, and in part will be obvious from the description, or may be learned by practice of the aspects described below. The advantages described below will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several aspects described below.

FIG. 1A shows representative OCT b-scans through the optic nerve head (ONH) of a tree shrew with segmented tissues. FIG. IB shows a sketch of tree shrew ONH showing investigated variables. FIG. 1C shows a box plot showing the effect of OCT camera position on the investigated variables. Changing the camera position by 5 mm had significant effect on Bruch membrane opening (BMO), retinal thickness at BMO and at the periphery (only posterior), and peripheral retinal pigment epithelium (RPE) position, but no significant effect on lamina cribrosa (LC) thickness. # paired t- test with p < 0.05.

FIG. 2 shows theoretical fan scanning image distortion and mapping between the (distorted) image space and the correct object space where: x = r sin(a) = (n + Ar) sin(a) z = r cos(a) - n = (n + Ar) cos(a) - n

Cl ^— (u — Umax/2) ⁽ Xmax/Umax ku Ar = (w-Wmax/2) k _w and where n, k _w , and k _u are unknown.

FIG. 3A shows the original OCT image of tree shrew posterior pole with implanted glass beads with known diameter of 100 pm within the retina. The spherical glass bead appears to be elliptical due to distortions in the OCT image. The yellow and red broken lines represented the segmented glass bead and retinal pigment epithelium (RPE), respectively. FIG. 3B shows the MRI image with segmented retinal curvature (red broken line) of the same tree shrew eye shown in FIG. 3A. FIG. 3C shows the distortion-corrected OCT images of scans from FIG. 3A with bead dimensions and RPE curvature that match the known bead diameter and MRI retinal curvature, respectively.

FIG. 4 shows the identified correlation between the angular scaling factor k _u and the theoretical Pivot point location n.

FIG. 5 shows the identified correlation between Spectralis OCT (Heidelberg Engineering) imaging parameters and the angular scaling factor k _u .

FIG. 6 shows validation of the disclosed method, showing the OCT images of one ONH at baseline position and after moving the OCT camera ± 5 mm. The images on the left-hand side were scaled using a linear scaling approach common to most commercial OCT devices. The images on the right-hand side show the distortion corrected images using the disclosed approach.

FIG. 7 shows a comparison between linear scaling (purple bars) and nonlinear distortion correction of the disclosed process (orange bars) on BMO and peripheral RPE position applied to the data shown in FIG. 1. In contrast to the linear scaling, the nonlinear distortion correction shows no significant difference in BMO and RPE position after moving the OCT camera 5 mm anterior or posterior compared to the baseline position. # paired t-test with p < 0.05.

DETAILED DESCRIPTION

Before the present compounds, compositions, articles, devices, and/or methods are disclosed and described, it is to be understood that the aspects described below are not limited to specific compounds, synthetic methods, or uses, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

In this specification and in the claims that follow, reference will be made to a number of terms that shall be defined to have the following meanings:

It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a glass bead” includes a plurality of glass beads, and the like.

“Optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event or circumstance occurs and instances where it does not. For example, the phrase “optionally includes an alternative reference marker” means that the alternative reference marker may or may not be present.

As used herein, the term “about” is used to provide flexibility to a numerical range endpoint by providing that a given value may be “a little above” or “a little below” the endpoint without affecting the desired result. For purposes of the present disclosure, “about” refers to a range extending from 10% below the numerical value to 10% above the numerical value. For example, if the numerical value is 10, “about 10” means between 9 and 11 inclusive of the endpoints 9 and 11.

Throughout this specification, unless the context dictates otherwise, the word “comprise,” or variations such as “comprises” or “comprising,” will be understood to imply the inclusion of a stated integer or step or group of integers or steps, but not the exclusion of any other integer or step or group of integers or steps. It is also contemplated that the term “comprises” and variations thereof can be replaced with other transitional phrases such as “consisting of’ and “consisting essentially of.”

“Biodegradable” materials are capable of being decomposed by bacteria, fungi, or other organisms, or by enzymes in the body of a subject.

“Biocompatible” materials are materials that perform their desired functions without eliciting harmful or deleterious changes to the subject in which they are implanted or to which they are applied, either locally or systemically. In one aspect, the polymers disclosed herein are biocompatible.

As used herein, “subject” refers to any organism having an eye wherein it is desirable to image the eye. In one aspect, the subject can be a bird or mammal including, but not limited to, a pet (e.g., dog, cat, guinea pig, rabbit, parrot, rat), a farm animal (e.g., sheep, cow, horse, goat, pig), a wild animal (e.g., tree shrew, squirrel, bat, chipmunk, raccoon, opossum, or the like), or a primate (e.g., gorilla, chimpanzee, bonobo, orangutan, New World monkey, Old World monkey, gibbon, lemur, baboon, or a human). In one aspect, the subject is a tree shrew. In another aspect, the subject can be a human.

“Optical coherence tomography” or OCT as used herein refers to an imaging technique that uses low-coherence light to capture 2D and 3D images from within optical scattering media such as, for example, biological tissue, with micrometer-scale resolution. OCT is a nondestructive method that requires little to no preparation of the sample or the subject that can be used for medical imaging and other applications. In one aspect, OCT is safe in that it does not require the use of ionizing radiation. In another aspect, OCT images can be obtained nearly instantly.

Disclosed are materials and components that can be used for, can be used in conjunction with, can be used in preparation for, or are products of the disclosed compositions and methods. These and other materials are disclosed herein, and it is understood that when combinations, subsets, interactions, groups, etc., of these materials are disclosed that while specific reference to each various individual and collective combination and permutation of these compounds may not be explicitly disclosed, each is specifically contemplated and described herein. For example, if a method for imaging a posterior segment of the eye is disclosed and discussed and a number of different compatible reference markers are discussed, each and every combination and permutation of imaging method and reference marker that is possible is specifically contemplated unless specifically indicated to the contrary. For example, if a class of molecules A, B, and C are disclosed as well as a class of molecules D, E, and F, and an example of a combination molecule, A-D, is disclosed, then even if each is not individually recited, each is individually and collectively contemplated. Thus, in this example, each of the combinations A-E, A-F, B-D, B-E, B-F, C-D, C-E, and C-F are specifically contemplated and should be considered disclosed from disclosure of A, B, and C; D, E, and F; and the example combination A-D. Likewise, any subset or combination of these is also specifically contemplated and disclosed. Thus, for example, the subgroup of A-E, B-F, and C-E is specifically contemplated and should be considered disclosed from disclosure of A, B, and C; D, E, and F; and the example combination A-D. This concept applies to all aspects of this disclosure including, but not limited to, steps in methods of making and using the disclosed compositions. Thus, if there are a variety of additional steps that can be performed, it is understood that each of these additional steps can be performed with any specific embodiment or combination of embodiments of the disclosed methods, and that each such combination is specifically contemplated and should be considered disclosed.

Method for Correcting a Distorted Image of a Segment in the Eye

3D morphological changes can be indicative of a variety of diseases of the eye including, but not limited to, glaucoma. Morphological changes associated with glaucoma involve a cupping or bowing of the lamina cribrosa within the optic nerve head at the back of the eye. Detection of 3D changes of the structure of the optic nerve head and retina can be vital in detecting early morphological changes and nerve fiber loss and/or other biomarkers indicative of glaucoma risk. Currently, no commercial posterior segment OCT device provides anatomically correct images.

In one aspect, disclosed herein is a method for correcting a distorted image of a segment in the eye of a subject produced by optical coherence tomography (OCT), the method including the following steps:

(a) scanning the segment of the eye using OCT to produce an OCT image;

(b) comparing the OCT image with at least one reference marker present at the segment of the eye; and

(c) performing distortion correction of the OCT image to produce an undistorted image of the segment of the eye. In another aspect, disclosed herein is the method described above, also including at least the following steps:

(a) imaging one or more anatomical segments in the eye with an imaging device to produce one or more second reference markers;

(b) scanning a segment of the eye using OCT to produce an OCT image;

(c) comparing the OCT image with the one or more second reference markers; and

(d) performing distortion correction of the OCT image to produce an undistorted image of the segment of the eye.

In another aspect, disclosed herein is the method described above, also including at least the following steps:

(a) administering to a segment of the eye a first reference marker having at least one known dimension;

(b) scanning the segment of the eye using OCT to produce an OCT image;

(c) comparing the OCT image with the first reference marker; and

(d) performing distortion correction of the OCT image to produce an undistorted image of the segment of the eye.

In another aspect, disclosed herein is the method described above, also including at least the following steps:

(a) administering to a segment of the eye a first reference marker having at least one known dimension;

(b) imaging one or more anatomical segments in the eye with an imaging device to produce a second reference marker;

(c) scanning the segment of the eye using OCT to produce an OCT image;

(d) comparing the OCT image with the first and second reference marker; and (e) performing distortion correction of the OCT image to produce an undistorted image of the segment of the eye.

In any of the above aspects, any commercial or experimental OCT device can be used in any of the above methods. In any of the above aspects, a computer system can be used to compare measurable and/or known dimensions of any reference marker to the OCT images produced. Further in this aspect, a computer system can be used to perform distortion corrections of the OCT images based on reference data gathered. Exemplary procedures for performing distortion corrections can be found in the Examples (see e.g., Examples 2 and 4). The computer system can be integrated or part of the OCT device or a separate, independent component of the system. In one aspect, the computing device includes software or code that can be embodied in any non- transitory computer-readable medium for use in the methods described herein (e.g., performing distortion correction of the OCT image to produce an undistorted image of the segment of the eye).

In one aspect, theoretical fan scanning image distortion and mapping between the (distorted) image space and the correct object space can be modeled using the following equations (see also FIG. 2): x = r sin(a) = (n + DG) sin(a) z = r cos(a) - n = (n + DG) cos(a) - n . — (u — Umax/2) ⁽ Xmax/Umax ku

DG = (w-Wmax/2) k _w and where n, k _w , and k _u are unknown.

In a further aspect, a 3D plot of OCT imaging parameters including the reference arm parameter (RAP) and scan focus (SF) reveals that k _w (axial scaling factor) is a constant, whereas k _u (angular scaling factor) can be determined or estimated from RAP and scan focus (see FIG. 5 and Example 4) and n (theoretical Pivot point location) can be determined from the correlation with ku (see FIG. 4 and Example 4). In one aspect, performing any of the disclosed methods produces an undistorted image. In a further aspect, the undistorted image is from 50% to 100% undistorted compared to the original, distorted OCT scan, or is greater than 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95% compared to the original or is 100% undistorted or a combination of any of the foregoing values, or a range encompassing any of the foregoing values. In a further aspect, percentage undistorted can vary the farther from the focal point or area of interest of the original OCT image. In an alternative aspect, the methods disclosed herein provide corrected OCT images that are equally undistorted in all areas of the images.

In another aspect, the disclosed methods do not require a detailed knowledge of the OCT system being used. In a further aspect, the disclosed methods do not require detailed knowledge of the eye being imaged.

Reference Markers

In one aspect, the methods disclosed herein use at least one reference marker. In another aspect, the reference marker can be or include a bead. In still another aspect, the bead can be a glass bead or a polymeric bead. In any of these aspects, the bead has a diameter of from about 25 to about 1000 pm, or of about 25, 50, 75, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or about 1000 pm, or a combination of any of the foregoing values, or a range encompassing any of the foregoing values. In one aspect, the bead has a diameter of about 100 pm. In one aspect, the reference marker is a plurality of beads having the foregoing dimensions.

In one aspect, the reference marker can be composed of a biodegradable polymer. In one aspect, the reference marker can be composed of bead composed of a biodegradable polymer. Examples of biodegradable polymer useful herein include, but are not limited to, a polylactide, a polyglycolide, a polylactide-co-glycolide, a polyesteramide, a polyorthoester, a poly-P-hydroxybutyric acid, a polyanhydride, a polydiene, a polyalkylene glycol, a polymethacrylate, a polyvinyl ether, a polyvinyl alcohol, a polyvinyl chloride, a polyvinyl ester, a polycarbonate, a polyester, a cellulose ether, a cellulose ester, a polysaccharide, a polycaprolactone, starch, or any combination thereof.

Polylactic acid is a polyester derived from lactic acid. The polyester is composed of lactic acid units depicted in the structure below, where m indicates the number of lactic acid units. The lactic acid unit has one chiral center, indicated by the asterisk (*) in the structure below:

Polylactic acid polymerization can begin from D or L lactic acid or a mixture thereof, or lactide, a cyclic diester. Properties of polylactic acid can be fine-tuned by controlling the ratio of D to L enantiomers used in the polymerization, and polylactic acid polymers can also be synthesized using starting materials that are only D or only L rather than a mixture of the two. Polylactic acid prepared from only D starting materials is referred to as poly-D-lactide (PDLA); conversely, polylactic acid prepared from only L starting materials is poly-L-lactide (PLLA).

As used herein, a D-lactic acid unit or an L-lactic acid unit refers to the monomer units within the polylactic acid polymers described herein, wherein a D-lactic acid unit is derived from the D-lactic acid or D-lactide starting material, and an L-lactic acid unit is derived from the L-lactic acid or L-lactide starting material as shown in the table below: Table 1 : Starting Materials for PDLA and PLLA

In another aspect, the reference marker can be an anatomical marker within the eye in order to avoid invasive implantation techniques. In another aspect, the reference marker. The known dimension of any reference anatomical marker used herein can be any measurable value such as, for example, radius, diameter, length, width, radius of curvature, or another dimension. This includes anatomical markers that are inherent of the eye anatomy such as the curvature of the retina, sclera and the distance between the fovea and optic nerve head.

In one aspect, the reference marker can be an anatomical distance, curvature or structure within the posterior segment. In another aspect, the reference marker can be within the posterior segment of the eye of the subject. In another aspect, the reference marker can be (1) curvature of the retina, (2) the distance between the optic nerve head and the fovea, or a combination thereof.

Imaging the Segment of the Eye

In certain aspects, the segment of the eye can be imaged to provide the first and/or a second reference markers described herein. In one aspect, the posterior segment of the eye imaged herein can be the retina, the optic nerve head, the macula, the fovea, the optic disc, the sclera, the choroid, a retinal blood vessel, or any combination thereof.

In another aspect, the segment of the eye in the methods disclosed herein can be imaged by magnetic resonance imaging; ultrasonography; fundus photography; angiography using fluorescein, indocyanine green, or fundus autofluorescence; or another method.

Applications

In a further aspect, the disclosed methods present an improvement over currently existing OCT technologies. In one aspect, the disclosed methods do not require modifications to existing OCT hardware, while current methods do require modification. In one aspect, the distance between the OCT camera and the eye is unknown in existing posterior segment OCTs. Further in this aspect, commercial OCT devices use a linear scaling approach to correct for magnification defects; but camera position relative to the eye being image can affect 3D morphometry displayed in the resulting images. In one aspect, existing methods for nonlinear distortion correction of posterior segment OCT images are based on numerical models of the optical imaging system and eye and require detailed knowledge of all optical components and their positions in 3D space. In one aspect, this data set is not fully available.

In one aspect, the disclosed methods can be applied to any existing posterior segment OCT that is based on a fan scanning approach. Also in this aspect, the distance between the OCT camera and the eye does not have to be known to employ the current method, since dimensions of the first and/or curvature of the second reference marker are known.

In one aspect, the disclosed method can be applied to established clinical devices without modification. In another aspect, the disclosed method can be applied to OCT data that has already been collected.

The methods described herein are useful in detecting and monitoring 3D morphological changes in a variety of diseases of the eye including, but not limited to, glaucoma. Morphological changes associated with glaucoma involve a cupping or bowing of the lamina cribrosa within the optic nerve head at the back of the eye. Detection of 3D changes of the structure of the optic nerve head and retina can be vital in detecting early morphological changes and nerve fiber loss and/or other biomarkers indicative of glaucoma risk and onset. By comparing two or more undistorted images of the segment of the eye produced by the methods described herein, eye diseases can be monitored over time if the subject has the eye disease. In other aspects, the onset of the eye disease can be evaluated using the methods described herein.

Aspects

Aspect 1. A method for correcting a distorted image of a posterior segment in the eye of an subject produced by optical coherence tomography (OCT), the method including the following steps:

(a) scanning the segment of the eye using OCT to produce an OCT image;

(b) comparing the OCT image with at least one reference marker present at the segment of the eye; and

(c) performing distortion correction of the OCT image to produce an undistorted image of the segment of the eye.

Aspect 2. The method of Aspect 1, wherein the method comprises

(a) imaging one or more anatomical segments in the eye with an imaging device to produce one or more second reference markers;

(b) scanning a segment of the eye using OCT to produce an OCT image;

(c) comparing the OCT image with the one or more second reference markers; and

(d) performing distortion correction of the OCT image to produce an undistorted image of the segment of the eye.

Aspect 3. The method of Aspect 1, wherein the method comprises

(a) administering to a segment of the eye a first reference marker having at least one known dimension;

(b) scanning the segment of the eye using OCT to produce an OCT image;

(c) comparing the OCT image with the first reference marker; and (d) performing distortion correction of the OCT image to produce an undistorted image of the segment of the eye.

Aspect 4. The method of Aspect 1, wherein the method comprises

(a) administering to a segment of the eye a first reference marker having at least one known dimension;

(b) imaging one or more anatomical segments in the eye with an imaging device to produce a second reference marker;

(c) scanning the segment of the eye using OCT to produce an OCT image;

(d) comparing the OCT image with the first and second reference marker; and (e) performing distortion correction of the OCT image to produce an undistorted image of the segment of the eye.

Aspect 5. The method of Aspects 3 or 4, wherein the first reference marker comprises a bead.

Aspect 6. The method of Aspect 5, wherein the bead comprises a glass bead or a polymeric bead.

Aspect 7. The method in any one of Aspects 5-7, wherein the bead has a diameter from about 25 pm to about 1,000 pm.

Aspect 8. The method in any one of Aspects 3-7, wherein the first reference marker is injected or implanted at the posterior segment of the eye. Aspect 9. The method in any one of Aspects 2-8, wherein the anatomical segment of the eye comprises the posterior segment of the eye.

Aspect 10. The method of Aspect 9, wherein the posterior segment comprises the retina, the optic nerve head, the macula, the fovea, the optic disc, a retinal blood vessel, the sclera, the choroid, or a combination thereof. Aspect 11. The method of Aspect 9, wherein the posterior segment comprises (1) curvature of the retina, (2) the distance between the optic nerve head and the fovea, or a combination thereof. Aspect 12. The method in any one of Aspects 1-11, wherein the anatomical segment of the eye is imaged by magnetic resonance imaging, ultrasonography, fundus photography, or angiography.

Aspect 13. A method for detecting changes 3D changes of an anatomical structure in an eye of a subject, the method comprising comparing two or more undistorted images of the segment of the eye produced by the method in any one of Aspects 1-12.

Aspect 14. The method of Aspect 13, wherein the subject has glaucoma.

Aspect 15. The method of Aspect 13, wherein the method can predict the onset of glaucoma. Aspect 16. A system, comprising: an optical coherence tomography device; and logic comprising the methods of any of Aspects 1-12, wherein the logic is stored on a non-transitory computer-readable medium.

Aspect 17. The system of Aspect 16, further comprising a computing device. Aspect 18. The system of Aspect 17, wherein the logic is executable on the computing device.

EXAMPLES

The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, and methods described and claimed herein are made and evaluated, and are intended to be purely exemplary and are not intended to limit the scope of what the inventors regard as their invention. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperatures, etc.) but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C or is at ambient temperature, and pressure is at or near atmospheric. Numerous variations and combinations of reaction conditions, e.g., component concentrations, desired solvents, solvent mixtures, temperatures, pressures, and other reaction ranges and conditions can be used to optimize the product purity and yield obtained from the described process. Only reasonable and routine experimentation will be required to optimize such processes and conditions.

Example 1: Nonlinear Distortion with Known Approaches

A commercial OCT device (Spectrlalis OCT2, Heidelberg Engineering) was used for animal research related to glaucoma and myopia. Nonlinear distortions were significant in these small animal eyes and the methods disclosed herein enable an understanding of the magnitude of these distortions and propose the approach described herein to correct these distortions. To investigate OCT distortions in tree shrews, we imaged the ONH of 14 tree shrew eyes. Baseline OCT images through the ONH were obtained and repeated after moving the OCT camera 5mm anterior and posterior. The tissues of the ONH were segmented and the following morphological features were obtained from the segmented data: lamina cribrosa (LC) thickness, Bruch membrane opening (BMO), retinal thickness as two locations and peripheral retinal pigment epithelium (RPE) position. These parameters are either known or suspected to be relevant biomarkers for glaucoma. FIG. 1 shows that moving the camera by 5mm most significantly changed BMO and RPE position. The magnitude of the observed changes is alarming and brings into question the reliability of previously published results on ONH changes seen in glaucoma. This pilot study illustrates the high need for a nonlinear distortion correction methodology for both, animal research and its application in the clinic.

Example 2: Theoretical Modeling

Posterior segment OCT devices use a fan scanning approach to image the posterior part of the eye. The fan of light rays converges in a pivot point as illustrated in FIG. 2. While the distortions that result from fan scanning are well known, a general applicable methodology for distortion correction has never been proposed. FIG. 2 also shows the main equations needed to map the image space into the anatomical correct object space. The transformation requires the knowledge of three parameters: the axial scaling factor k _w , angular scaling factor k _u and the pivot point location n. Prior approaches have used numerical models to establish distortion corrections, but using reference markers inside the eye to empirically establish a relationship between the three unknown parameters and known imaging parameters is a superior and novel approach, as shown herein. The disclosed method can be applied to any OCT system and does not require knowledge of the optical system.

Example 3: Implantation of Glass Beads and Their Use as Reference Markers

Glass beads of known diameter (100 ± 2.7 pm) were implanted into or on top of the retina of 5 tree shrews. The Spectralis OCT2 (Heidelberg Engineering) was used to acquire 234 B-scans through the center of the beads in the same animals using a wide range of camera settings (camera position, focus, and reference arm position). The implanted glass beads can be seen in the OCT images and serve as one reference marker to establish the image distortion correction (FIG. 3A). Note that the spherical glass bead appears elliptical in this distorted image. A second reference marker is the curvature of the retinal pigment epithelium (RPE), which was obtained from MRI imaging (FIG. 3B). The Spectralis records several imaging parameters, two of which include the reference arm parameter (RAP) and the scan focus (SF). Similar parameters can be obtained from other OCT systems. The distorted glass bead dimensions and RPE curvature were first quantified. The three unknown parameters of the distortion correction approach (FIG. 2) were identified for each scan by finding the best fit comparing the bead dimension and RPE curvature of the distortion corrected image with the actual known bead diameter and MRI retinal curvature (i.e. ground truth), respectively (FIG. 3C).

Example 4: Identification of Axial Scaling Factors k _w and k _u and Pivot point location n

One of the three unknown (see FIG. 2) parameters was identified as constant: the axial scaling factor k _w . A clear non-linear correlation between the angular scaling factor k _u and the position of the pivot point location n was identified (R ² : 0.9993, FIG. 4). This correlation was found to be independent of the scan parameters suggesting that only one parameter needs to be identified from the scan settings to establish the distortion correction. FIG. 5 shows that the angular scaling factor k _u can be estimated with high accuracy (R ² =0.9079) from the imaging parameters RAP and SF of the Spectralis. Alternatively, to the correlation between RAP and SF and k _u shown in FIG. 5, the angular scaling factor k _u (or the Pivot point location n) can be identified for every OCT scan from an anatomical marker within the eye (e,g, retinal curvature, fovea, macula, optic nerve head) and the Pivot point location n (or angular scaling factor k _u ) from the correlation shown in FIG 4. Once these correlations have been established, distortion correction can be performed on OCT scans using the same imaging setup and species.

Example 5: Distortion Correction on Tree Shrew Eye Images

To illustrate the disclosed approach, the OCT images used to illustrate nonlinear distortions in FIG. 1 were distortion corrected. FIG. 6 shows representative scans of one tree shrew ONH after linear scaling (left column). This is a method used by most commercial OCT devices and leaves images distorted as well as leading to inaccurate conclusions when used in research or studies. This can be compared to the distortion corrected images (FIG. 6; right column). While large distortions are clearly visible in the linear scaling approach when the camera position is moved anterior and posterior from baseline, there are no obvious differences seen after applying the distortion correction as described herein.

Example 6: Comparison of Linear Scaling and Nonlinear Distortion Correction

Additionally, a validation set of images was used to objectively compare anatomic measures in images after linear scaling correction with the disclosed approach. The results show a significant difference in BMO and peripheral RPE position when using linear scaling. However, there were no significant differences in BMO and peripheral RPE position between can positions after applying the disclosed distortion correction (FIG. 7). A similar distortion correction can be established for other OCT devices and other species using the disclosed method. Throughout this application, various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the compounds, compositions, and methods described herein. Various modifications and variations can be made to the compounds, compositions, and methods described herein. Other aspects of the compounds, compositions, and methods described herein will be apparent from consideration of the specification and practice of the compounds, compositions, and methods disclosed herein. It is intended that the specification and examples be considered as exemplary.