Age-related differences in ocular features of a naturalistic free-ranging population of rhesus macaques

ABSTRACT Purpose Rhesus macaques ( Macaca mulatta ) are the premier nonhuman primate model for studying human health and disease. We aimed to investigate if age was associated with ocular features of clinical relevance in a large cohort of free-ranging rhesus macaques from Cayo Santiago, Puerto Rico. Methods We evaluated 120 rhesus macaques (73 males, 47 females) aged from 0 to 29 years old (mean±SD: 12.6±6.4) from September to December, 2021. The ophthalmic evaluation included IOP assessment, corneal pachymetry, anterior segment biomicroscopy, A-Scan biometry, automated refraction, and fundus photography after pupil dilation. The effects of age on the outcome variables were investigated through multilevel mixed-effects models adjusted for sex and weight. Results On average, IOP, pachymetry, axial length, and automated refraction spherical equivalent were 15.47±2.47 mmHg, 474.43±32.21 μm, 19.49±1.24 mm, and 0.30±1.70 D, respectively. Age was significantly associated with pachymetry (Coef.= -1.20; 95%CI: -2.27 to -0.14; p=0.026), axial length (Coef.= 0.03; 95%CI: 0.01 to 0.05; p=0.002), and spherical equivalent (Coef.= -0.12; 95%CI: -0.22 to -0.02; p=0.015). No association was detected between age and IOP. The prevalence of cataracts in either eye was 10.83% (95% CI: 6.34 – 17.89%) and was significantly associated with age (OR= 1.20; 95%CI: 1.06 – 1.36; p=0.004). Retinal drusen in either eye was observed in 15.00% (95% CI: 9.60 – 22.68%) of the animals, which was also significantly associated with age (OR=1.14; 95%CI: 1.02 – 1.27; p=0.020). Conclusions Rhesus macaques exhibit age-related ocular associations similar to those observed in human aging, including decreased corneal thickness, increased axial length, myopic shift, and higher occurrence of cataract and retinal drusen.