Abstract
Purpose :
To study changes in the birefringent properties of human cornea across healthy, thin corneas (< 500 µm), asymmetric and clinical KC.
Methods :
In this study, the birefringent properties of 40 eyes from 20 subjects divided across 4 groups (healthy, thin, asymmetric KC and clinical KC corneas) were measured using our custom-built ultrahigh-resolution PS-OCT. Groups-1, 2 and 4 consisted of 10 eyes from 5 subjects each. Group-3 consisted of 5 eyes that showed normal topographical features, while their fellow eye showed classical KC features were put in Group-4 along with eyes having bilateral clinical KC. To achieve a near limbal-to-limbal scan field with uniform signal strength throughout the cornea a conical scan setup was incorporated in the PS-OCT design. Phase retardation (PR) enface maps from the posterior surface of the cornea were generated to obtain a succinct representation of the corneal fibril distribution.
Results :
Figure-1 shows the PR enface maps of representative cases from each group and their corresponding axial curvatures (AC) maps. Columns 1 and 2 represent maps from a healthy cornea and a thin cornea. Columns 3 and 4 are from the same subject, with OD being the KC eye and OS being the contralateral eye having normal topography. While column 5 constitute the clinical KC eye. PR enface maps of healthy corneas showed the preferential arrangement of collagen fibrils with least retardation in apex and anchoring fibrils in the periphery. Thin corneas mimicked healthy eyes in collagen fibrillar arrangement. Asymmetric KC eyes followed common definitions of sub-clinical and forme fruste KC, but PR maps from PS-OCT confirmed a near-healthy collagen fibrillar distribution in these eyes. Clinical KC corneas showed large disruptions in collagen fibrillar arrangement at all annular zones (p<0.05) with complete loss of peripheral anchoring fibrils.
Conclusions :
Distinctive changes in the structural arrangement of collagen fibrillar distribution were observed in KC, thin corneas, and healthy eyes. Spatial variations (zonal analyses) in polarization-sensitive information can assist in effectively minimizing the susceptive, erroneous classifications between healthy and diseased corneas in a clinical setting.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.