Early Structural Changes in Keratoconic Eyes After Corneal Crosslinking Detected by Polarization-Sensitive Optical Coherence Tomography.

Abstract

To assess early structural changes in keratoconic corneas secondary to epi-off corneal crosslinking (CXL) using polarization-sensitive optical coherence tomography (PS-OCT). Interventional case series. Eight eyes of 8 subjects with bilateral keratoconus were included. Epi-off CXL using 10 minutes of hydroxypropyl methylcellulose-based riboflavin soaking before 10 minutes of ultraviolet irradiation (9 mW/cm²) was performed. Eyes were imaged using conventional Scheimpflug, anterior-segment optical coherence tomography (AS-OCT), and PS-OCT imaging. PS-OCT raster scanning was performed before (baseline [BSL]) and immediately after CXL, and 1 week, 1 month, and 3 months after CXL. Degrees of polarization uniformity (DOPU) images of each visit were evaluated as indicator for structural changes. Findings were compared with corresponding AS-OCT imaging. Scheimpflug and AS-OCT imaging revealed expected CXL-induced changes in corneal curvature (compared with BSL: Kmax increase at 1 month, P = .01; Kmax decrease at 3 months, P = .02) and the appearance of a demarcation line 1 month after CXL followed by normalization of the corneal structure. PS-OCT revealed a distinct, time-dependent pattern of polarization-maintaining backscattering in the corneal stroma secondary to CXL. At 1 week, ring-shaped polarization preservation appeared: anterior stroma DOPU 0.720 ± 0.015, mid-stroma 0.767 ± 0.016 (P < .01), and posterior 0.744 ± 0.010. At 1 month, DOPU values were 0.745 ± 0.017, 0.779 ± 0.023 (P > .05 vs 1 week), and 0.802 ± 0.016 (P = .001 vs 1 week), respectively, with decreasing ring diameters (P = .03 anterior vs mid; P = .04 posterior vs 1 week). At 3 months, DOPU decreased to 0.669 ± 0.007 (P < .001 vs 1 month), 0.688 ± 0.011 (P < .001 vs 1 month; P = .05 vs BSL), and 0.734 ± 0.019 (P < .001 vs 1 month), indicating evolving stromal structural changes post-crosslinking. By using PS-OCT, the tissue response to CXL 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 and mid but also in the 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 nonresponders.