Advanced corneal imaging and corneal endothelial cell parameters in rhesus macaques (Macaca mulatta)

Abstract

Purpose : Non-human primates offer a significant advantage in the study of the pathogenesis and therapeutics for corneal disease because of their ocular similarity to humans. This study aims to define the range of normal central corneal thickness (CCT) and corneal endothelial cell density (ECD) in rhesus macaques (Macaca mulatta) and to determine the effect of age, body weight, and sex on these parameters.

Methods : Ophthalmic examination was performed in 144 rhesus macaques without corneal or anterior chamber lesions. The range of age of the primates examined was 0.2-29.4 years (mean 13.7 ± 7.1 years); 98 were females and 46 were male. The ECD was semi-automatically counted and manually counted using in vivo specular microscopy while CCT was measured via ultrasound pachymetry (USP). Linear regression model and mixed effects linear regression were used to evaluate the main effects of age, body weight, sex, intraocular pressure (IOP) and axial length of the globe (AXL) and refractive error on CCT and ECD. A concordance correlation coefficient (CCC) was calculated to estimate the reliability of semiautomatic versus manual counts. Linear regression with mixed effects linear regression were used to evaluate the main effects of an individual’s body weight, age and sex on corneal thickness and corneal endothelial cell density.

Results : Mean ECD was 2717 ± 423 cells/mm², similar to the reported range for humans in early adulthood at approximately 2500 cells/mm². Mean CCT was 483 ± 39 µm, which was similar to that documented for humans at 534.8 ± 34.7 µm. IOP and sex were statistically significantly associated with CCT, while body weight, age, and AXL were associated with ECD (p < 0.05). There was good reliability between semiautomatic and manual ECD counts (CCC=0.79). There was no significant correlation between CCT and ECD (p=0.89).

Conclusions : The rhesus macaque has similar corneal characteristics when compared to humans and can thus serve as an ideal model to study corneal endothelial cell disorders and corneal diseases. This study suggests a normal range of ECD from 2294-3140 cells/mm² and 444-522 µm for CCT in rhesus macaques (Macaca mulatta).

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