Ex-vivo imaging of the posterior human corneal layers after Big Bubble DALK and DMEK procedures with sub-micrometer axial resolution OCT

Abstract

Purpose : To examine the structural integrity of the posterior corneal layers after big-bubble deep anterior lamellar keratoplasty (BB-DALK) and Descemet’s Membrane endothelial keratoplasty (DMEK) procedures by imaging ex-vivo human corneas with sub-micrometer axial resolution OCT and comparing the OCT images with histology.

Methods : A research grade sub-micrometer axial resolution OCT system was used to image ex-vivo the human posterior corneal layers. Human cadaver corneas were obtained from the Eye Bank of Canada (n = 29). A BB-DALK was formed after intrastromal injection of air into the donor corneoscleral button in 24 of the corneas, while the remaining 5 served as controls. After the procedure, the endothelial layer was covered with Dispase at 4°C for (16-20 hours) then rinsed with buffer solution to remove the endothelial layer. Volumetric OCT images ( 512 A-scans x 512 B-scans) were acquired from 10 mm x10 mm area of the central cornea with 0.95 µm axial and ~5 µm lateral resolution, before and immediately after the BB-DALK procedure and after 18h treatment with Dispase. Custom, Matlab-based image processing algorithms were used to numerically dispersion compensate the OCT images. After the OCT imaging session, the corneal tissue samples were processed for histological analysis. Pre and post imaging of similar corneas for DMEK procedures will also be performed later this month.

Results : Out of the 24 corneas injected with air, Type-1 BB (pre-Descemet’s layer (PDL) with Descemet’s membrane (DM)) was formed in 10 corneas, Type-2 BB (DM alone) and Mixed BB were formed in 3 corneas each, while the remaining 8 cornea were injected with Viscoat to create or maintain ruptured BB. OCT images of the posterior corneal layers of both Type-1 BB and Type-2 BB showed double contour line. In Type-1 BB, the anterior line was thicker and more hyper-reflective. Re-imaging the posterior corneal surface after chemical removal of the endothelium with Dispase continued to show the double contour line, however, the posterior line was less hyper-reflective.

Conclusions : Comparison of the high resolution OCT images and histology shows that Type 1 and Type 2 BB cause different structural damage to the PDL and DM. These findings may help with the development and interpretation of intraoperative high resolution OCT for lamellar corneal surgery.

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