Normal Corneal Thickness and Endothelial Cell Density in Rhesus Macaques (Macaca mulatta)

Purpose: To define the normal range of central corneal thickness (CCT) and corneal endothelial cell density (ECD) in rhesus macaques (Macaca mulatta) and the effects of age, body weight, sex, and intraocular pressure (IOP) on these parameters. Methods: Ophthalmic examinations were performed on 144 rhesus macaques without anterior segment pathology. The CCT was measured via ultrasound pachymetry (USP) and specular microscopy, and the ECD was semiautomatically and manually counted using specular microscopy. Rebound tonometrywas used to measure IOP. Linear regression andmixed- effects linear regression modelswere used to evaluate the effects of age, body weight, sex, and IOP on CCT and ECD. Results: We included 98 females and 46 males with an age range of 0.2 to 29.4 years. Themean CCT by USP and specular microscopywere 483 +/- 39 and 463 +/- 33 mu m, respectively, andwere statistically different (P< 0.001). The ECDswere 2717 +/- 423 and 2747 +/- 438 cells/mm(2) by semiautomated and manual analysis, respectively. Corneal endothelial degeneration was identified in one aged rhesus macaque. Conclusions: The mean USP and specular microscopy CCT values differed significantly, whereas the semiautomatic and manual ECD did not. The CCT was associated with the IOP and sex, whereas the ECD was associated with body weight and age (P < 0.05). As in humans, corneal disease in rhesus macaques is uncommon. Translational Relevance: Establishing reference values is fundamental to use rhesus macaques as amodel for corneal disease or to identify toxicity in studies of ocular drugs or devices.