Abstract
Purpose :
Today, there is evidence that the Bowman’s Layer (BL) shows signs of disintegration and pathological thinning in eyes with keratoconus (KC) before the corneal stroma is affected. Theoretically, even before changes of the epithelial thickness (ET) can be visualised. Aim of this study was to evaluate ET and BL thickness (BLT)-changes using polarization sensitive (PS)-optical coherence tomography (OCT) in patients with unilateral keratoconus.
Methods :
Unilateral KC was confirmed if the keratoconic eye showed topographic findings considered as typical for KC like corneal thinning, central or inferior steep zone and asymmetric bowtie with or without skewed axis astigmatism, whereas the corresponding eye showed no topographical changes. A custom built large field of view (FoV)-PS-OCT with a conical scanning optics design (axial resolution ~ 6.3 µm) was used to scan patients with unilateral KC. Automated segmentation of the corneal stroma, epithelium and BL was performed B-scan wise. Individual corneal layers were detected and delineated in a field of view of 11mm due to the conical scanning optics design and the assessment via two orthogonal channels (Figure 1). Custom made software was used to plot 11mm diameter ET- and BLT en-face maps.
Results :
Twenty-four eyes of 12 patients with unilateral KC were scanned. The en-face ET-maps of keratoconic eyes showed a “doughnut profile”, whereas the ET-maps of healthy eyes showed no irregularity. En-face BLT-maps showed signs of irregularity in both, keratoconic eyes and healthy eyes (Figure 2).
Conclusions :
The need for screening parameter for the early detection of KC is indisputable. Irregularities of the Bowman’s layer thickness that was observed in this study population could be a biomarker for the early detection of KC. However, the predictive value of ET maps and BLT assessment as early screening methods remain to be elucidated in future longitudinal studies with larger sample sizes of patients with unilateral keratoconus.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.