Sterile donor tomography for improvement of refractive results after keratoplasty

Abstract

Purpose: Any corneal microsurgeon may have inadvertently transplanted a donor corneal tissue with (subclinical) keratoconus or prior keratorefractive surgery, which typically leads to postoperative refractive surprises and cannot always be detected in the eye bank with only slit lamp. Given the increased number of keratorefractive procedures performed in the last decades, eye banks will soon have to face this problem more intensively. Thus, the efficiency and reliability of anterior segment optical coherence tomography (AS‐OCT) as a non‐invasive and sterile screening method in the eye bank to detect corneal grafts with curvature and/or thickness abnormalities was assessed.Methods: 1315 donor corneal tissues mounted in sterile tissue cultivation flasks were imaged using an AS‐OCT. The corneal tissues were preserved in organ culture medium I and transferred into organ culture medium II (containing dextran T‐500 6%) for deswelling at least 24 h prior to measurement and keratoplasty. Depth raster scans were performed through the posterior surface of the corneal tissues within a 7 mm central zone to create 3D volume data. The volume data set was preprocessed to eliminate flask reflections artefacts and to define the region of interest (ROI). Subsequently, the adaptation of a sphero‐cylindrical surface model was carried out with raytracing. Thus, the radii of curvature for the front and back surfaces can be determined and a corneal thickness map is generated.Results: The mean steep/flat front surface radius was 7.46 ± 0.29 (5.07–9.29)/7.69 ± 0.24 (6.70–9.50) mm, the corresponding values for the back surface being 6.47 ± 0.32 (5.00–8.00)/6.80 ± 0.31 (5.81–8.00) mm and the mean central thickness was 610 ± 84 (379–1457) μm. Abnormalities (beyond ±2 or ± 3 SD) were found in 140 or 34 corneas (10.6% or 2.6%) for anterior surface curvature, 120 or 38 corneas (9.1% or 2.9%) for the posterior surface, and 55 or 16 corneas (4.2% or 1.2%) for thickness.Conclusions: The AS‐OCT provides an objective, sterile and semi‐automated screening method to identify corneal morphological and refractive alterations (e.g. keratoconus, status post PRK/LASIK) and further optimize corneal donor selection in the eye bank. Corneal donors with curvature or thickness abnormalities ±3 SD do not have to be discarded but can be used for posterior lamellar keratoplasty or tectonic keratoplasty.