Early structural changes in keratoconic eyes after corneal crosslinking detected by polarization sensitive optical coherence tomography

Abstract

Purpose : To assess early structural changes in keratoconic corneas secondary to epi-off corneal crosslinking (CXL) using polarization sensitive optical coherence tomography (PS-OCT).

Methods :
Thirty eyes of 30 subjects with bilateral keratoconus were imaged using conventional anterior segment (AS-)OCT and PS-OCT imaging. PS-OCT raster scanning was performed prior to as well as immediately after, 4 days and 1 month after CXL. Reflectivity images, as well as co-polarized, cross-polarized and retardation images of each visit were evaluated for structural changes. Findings were correlated with corresponding AS-OCT imaging.

Results : At baseline, depolarization of backscattered light in all stromal layers along the visual axis as well as in the anterior layers of the entire stroma could be observed by the green color in the retardation image that indicates approximately equal amplitude in the co- and cross-polarized channels (Fig 1A).
Immediately after CXL a clear delineation of polarization preserving tissue (blue color) was seen in the anterior stroma (36.7 ± 7.2% depth) in all patients (Fig 1, B2 arrow heads). Deeper layers of the cornea remained unaltered.
At day 4 after CXL the delineation of depolarizing stroma became less distinct but extended deeper into the corneal tissue (43.2 ± 8.9% depth) (Fig 1C).
One month after CXL all corneas presented a striking ring-shaped polarization preserving pattern (Fig 1, D2 & D3 asterisks; red line in D2 indicating location of enface projection in D3). The pattern started at the peripheral anterior limits of the original CXL UV-A irradiation and reached the descemet’s layer in all cases but one (96.7%).
When comparing with corresponding AS-OCT images the ring-shaped patterns were found in the region of the demarcation line (Fig 1, D4 arrows), however were less delineated and reached much deeper into the stroma.

Conclusions : Using PS-OCT, tissue response to corneal crosslinking of keratoconic eyes was investigated in high detail, taking advantage of the polarizing properties of corneal tissue. Findings suggest a more profound restructuring not only in the anterior but also deep and posterior stroma after CXL than previously described in the literature. Such new morphologic signs might serve as future biomarkers to predict therapeutic outcomes or detect non-responders.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.