Investigating the effects of surgical intraocular pressure on corneal endothelial cell viability using intact porcine eyes

Abstract

Purpose : Although it is widely accepted that corneal endothelial cell (CEC) damage occurs during phacoemulsification surgery, it remains unclear if the elevated intraocular pressure (IOP) used during phacoemulsification contributes significantly to this damage. Using a novel experimental method enabling quantification of CEC damage in intact porcine eyes, we tested the hypothesis that elevated IOP under conditions relevant to phacoemulsification surgery leads to increased CEC damage.

Methods : Corneal endothelia of fresh, intact explanted porcine eyes were stained with two nucleic acid viability dyes and imaged through a fluorescence microscope without removing the cornea from the globe. The anterior chambers of the eyes were perfused with BSS to a pressure of 73.6mmHg (bottle height=100cm) for 10min (n=4) prior to restaining and reimaging. Baseline images were analyzed using custom algorithms to determine initial total cell counts (TC₁) and damaged/dead cell counts (DC₁). Images acquired after pressurization were analyzed to obtain final cell counts (TC₂, DC₂). CEC damage was quantified as the change in percent of cell damage/death, PCD (PCD=100*DC₂/TC₂–100*DC₁/TC₁). As a negative control, additional eyes were pressurized to a physiological IOP of 18.4mmHg for 10min (n=4). The experimental and negative control groups were compared using a two-tailed Student's t-test. As a positive control, one eye was perfused with deionized water at a pressure of 18.4mmHg for 10min.

Results : There was no significant difference in mean PCD values between the experimental (0.22%) and negative control (0.30%) groups (p=0.78). The positive control sample yielded a PCD of 84.5%, indicating that the method is able to detect CEC damage.

Conclusions : Our results suggest that the elevated IOP used over the duration of phacoemulsification surgery does not lead to a significant increase in CEC damage. However, further studies are needed to expand the sample size and ensure statistical power. Notably, the mean PCD measured in the experimental group was less than the yearly decrease in the central CEC density of healthy individuals (0.59%), strongly suggesting that surgical IOP alone does not result in clinically-significant CEC damage.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

 

Figure 1: Representative (A) processed corneal endothelial image and (B) zoomed in view where individual nuclei are visible.

 

Figure 2: Comparison of CEC damage across groups.