Comparison of corneal epithelial thickness before and after corneal cross-linking surgery with and without intracorneal ring segments using optical coherence tomography

Abstract

Purpose : Corneal cross-linking (CXL) is a surgical treatment option that can decrease the progression of keratoconus (KC) and can be combined with intracorneal ring segment (ICRS) insertion in an attempt to improve refractive outcomes. In vivo imaging of KC patients using optical coherence tomography (OCT) was performed to compare total and corneal epithelial thicknesses before and after CXL and CXL+ICRS surgeries.

Methods : There were 11 KC eyes that underwent CXL and 10 KC eyes that had CXL+ICRS surgery. All eyes were imaged before surgery and 6 and 12 months after surgery. Images were acquired using a research grade swept source OCT system which provided 5µm axial, ~15µm lateral resolution, and ~4mm scanning depth in corneal tissue. Volumetric images of the KC cornea were acquired at the speed of 100,000 A-scans/sec. The images were analyzed with a novel image processing algorithm that segmented the anterior and posterior surfaces of the cornea, and the posterior epithelium. The epithelial and total thicknesses at the point of minimum total thickness and four adjacent locations were obtained for comparison.

Results : The CXL+ICRS group showed a greater epithelial thickness than the CXL only group (p=0.01) and both groups demonstrated increased epithelial thickness after surgery, though there was only a significant difference between visits 1 and 4 (p=0.004) and not for visits 1 and 3 (p=0.22) or 3 and 4 (p=0.27). There were no significant differences in epithelial thickness between the five adjacent zones used in this study. The CXL+ICRS group also showed greater total corneal thickness measurements than the CXL group (p<<0.05). The total corneal thickness increased after surgery for both groups and the difference was only significant for visits 1 and 4 (p<<0.05) and not visits 1 and 3 (p=0.05) or 3 and 4 (p=0.07). There were significant differences in total thickness according to location with the central zone found to be thinner than the superior (p=0.05), inferior (p=0.02), and nasal (p=0.04) zones, but not the temporal zone (p=0.16).

Conclusions : Epithelial and total corneal pachymetry measurements before and after CXL and CXL+ICRS surgery for KC showed an increase in thickness after surgery with the CXL+ICRS group having thicker total and epithelial measurements compared to the CXL only group.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.