Corneal Thickness and Endothelial Cell Density in Rhesus Macaques (Macaca mulatta) with Laser Induced Ocular Hypertension

Abstract

Abstract: : Purpose: The sustained ocular hypertension in humans causes a loss of corneal endothelial cells and an increase of corneal thickness. Increased corneal thickness can affect intraocular pressure (IOP) measurements. The effects of chronic elevated IOP on the cornea are not documented in monkeys with experimental laser-induced ocular hypertension, a commonly used animal model of human glaucoma. This study examined the central corneal thickness (CCT), and the corneal endothelial cell density (ECD) in Rhesus monkeys with experimental ocular hypertension. Methods: Ten male monkeys with argon laser-induced ocular hypertension in one eye were sedated with ketamine hydrochloride, and CCT and ECD measured at the center of the cornea of both eyes with a Topcon SP-2000P ^TM non-contact specular microscope (Topcon America Corporation®, Paramus, NJ, U.S.A). Mean and standard deviation (SD) of CCT and ECD for each eye was calculated and statistically compared. Results: The age (mean SD) of these animals was 6.7 1.4 years. An average of 2.3 1.0 laser sessions had been necessary to maintain an increased IOP of 38.3 10.8 mm Hg in the right eye (versus 14.8 0.8 mm Hg in the normal eye) for 2.4 0.7 years.Mean CCT in the glaucoma and normal eyes was 0.468 0.02 and 0.477 0.023 mm respectively. Mean ECD in the hypertensive and normal eyes was 2601.7 631.8 and 3990.2 402.9 cells/mm₂ respectively. The size of the endothelial cells varied from 278.1 to 638.5 µm₂ with an average of 408.7 115.0 µm₂ in the normal eye. In the hypertensive eye, the mean cell size was 252.4 23.9 µm₂ with a range between 161.7 and 432.2 µm₂. No significant difference of the mean CCT was observed between the two eyes (p=0.4820) whereas the mean ECD was significantly lower (33% decrease) 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). Conclusion: The chronic ocular hypertension did not affect the corneal thickness but it caused a significant loss of endothelial cells in the center of the cornea of the laser treated eyes compared to the normotensive eyes. Furthermore, the duration of elevated IOP was the most important factor influencing the endothelial cell density.

Keywords: 316 animal model • 371 cornea: endothelium • 444 intraocular pressure