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 micras, 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.

The biology of aging in a social world: insights from free-ranging rhesus macaques

“…Rhesus macaques are particularly well suited for eye-related studies since they share several ocular features with humans that are absent in classic rodent and rabbit models. Eye exams demonstrate older macaques on Cayo have thinner corneas, greater axial length, and less myopic shift compared to younger individuals, indicative of age-related ocular variation that is also observed in humans (Fernandes et al, 2022; Galgauskas et al, 2013; McCullough et al, 2020; Verkicharla et al, 2020). Incidence of cataracts and retinal drusen are also significantly higher in older individuals than younger conspecifics (Fernandes et al, 2022).…”

“…Eye exams demonstrate older macaques on Cayo have thinner corneas, greater axial length, and less myopic shift compared to younger individuals, indicative of age-related ocular variation that is also observed in humans (Fernandes et al, 2022;Galgauskas et al, 2013;McCullough et al, 2020;Verkicharla et al, 2020). Incidence of cataracts and retinal drusen are also significantly higher in older individuals than younger conspecifics (Fernandes et al, 2022). Longitudinal studies will be necessary to determine whether these changes truly represent markers of aging rather than arising from population-level factors such as differential mortality (i.e., selective disappearance) (Nussey et al, 2008).…”