Corneal thickness and endothelial cell density measured by non-contact specular microscopy and pachymetry in Rhesus macaques ( Macaca mulatta) with laser-induced ocular hypertension

Abstract

Purpose. Sustained increase in intraocular pressure (IOP) in humans results in a loss of corneal endothelial cells and an increase of corneal thickness. The effects of chronically elevated IOP on the corneal endothelium of monkeys with laser-induced ocular hypertension, a commonly used animal model of human glaucoma have not been documented. This study examined the central corneal thickness (CCT), the corneal endothelial cell density (ECD), and the corneal endothelial cell size (ACS) in Rhesus monkeys with experimental ocular hypertension. Materials and methods. Ten male monkeys with argon laser-induced ocular hypertension in one eye for an average duration of 2·4±0·7 years, were sedated with ketamine hydrochloride, and the CCT, ECD, and ACS measured at the center of the cornea of both eyes with a Topcon SP-2000P™ non-contact specular microscope (Topcon America Corporation ®, Paramus, NJ, USA). CCT was also measured using a DHG-500 Pachette™ ultrasonic pachymeter (DHG Technology Inc., Exton, PA, USA). Mean and standard deviation ( s.d.) of CCT, ECD and ACS for each eye was calculated and statistically compared. Results. Mean CCT in the hypertensive and normal eyes measured by specular microscopy was 0·477±0·023 mm and 0·468±0·020 mm, respectively. Mean ECD in the hypertensive and normal eyes was 2601·7±631·8 and 3990·2±402·9 cells mm −2, respectively. The mean size of the endothelial cells was 252·4±23·9 μm 2 in the normal eye and 408·7±115·0 μm 2 in the hypertensive eye. No significant difference in the measurement of CCT was observed between the specular microscope and the pachymeter ( p=0·46). No significant difference in the mean CCT was observed between the two eyes ( p=0·4820), whereas the mean ECD was significantly lower in the hypertensive eye than in the normal eye ( p<0·001). The ECD was inversely related to the length of IOP elevation ( p<0·001). Conclusions. No difference in the corneal thickness measurement was observed between the specular microscopy and the pachymetry techniques. Chronic ocular hypertension did not significantly affect the CCT, but caused a significant loss of endothelial cells in the center of the cornea of the laser treated eyes compared to the normotensive eyes. The duration of elevated IOP was the most important factor affecting the ECD.