Polarization Sensitive Optical Coherence Tomography (Psoct) - A New Tool In Refractive Surgery Screening

To establish the in-situ collagen fibre distribution in healthy and keratoconus (KC) corneas and correlate with early disease related collagen fibre changes in suspect corneas

Department of Cornea and Refractive Services at Narayana Nethralaya, Bangalore

A total of 150 healthy, 150 KC and 50 suspect corneas were imaged prospectively with ultra-high-resolution polarisation sensitive (PS) OCT. Additionally, 35 asymmetric fellow corneas of KC patients were also imaged. These asymmetric fellow corneas were subclinical in nature upon clinical examination (slit lamp and corneal tomography) by an experienced surgeon. Phase retardation (PR) enface maps from the posterior surface were generated. Zonal analysis was performed on the enface maps in annular zones from centre to periphery.

PR maps of normal eyes showed preferential arrangement of collagen fibrils, with least retardation in apex (210) and increasing gradually towards periphery (470). Suspect corneas showed visibly different arrangement. Zonal analysis showed higher pr in suspects compared to normal eyes, which was statistically significant. (p<0.05)

PS-OCT identified differences in collagen distribution in normal and suspicious corneas, possibly indicating weaker biomechanics. PS-OCT can be used in clinical settings for early diagnosis of KC in normal/suspicious topography and screening for refractive procedures.