Age effects on ocular features of rhesus macaques

Abstract

Purpose : Rhesus macaques (Macaca mulatta) are a valuable model in ophthalmology research, exhibiting visual systems that share many anatomical similarities with those of humans. The purpose of the current study is to investigate the effects of age on ocular features of a large cohort of free ranging rhesus macaques derived from animals originally introduced to Cayo Santiago/Puerto Rico in 1938.

Methods : A total of 172 animals (83 males and 89 females) from all ages (mean 13.1±5.7; range 0.7 to 26.2 years old) and mean weight of 16.0±7.6 pounds underwent a comprehensive eye exam, including slit-lamp biomicroscopy (HSL-600, MicroClear, Jiangsu, China), pachymetry (Pachmate 2, DGH Technologies, Exton, USA), axial length (vuPad, Sonomed Escalon, Lake Success, USA), and automated refraction (Topcon KR 7000S, Topcon, Tokyo, Japan). Each outcome variable was modeled as a function of age using multilevel mixed-effects models adjusted for animal sex and weight.

Results : Cataract of any degree (no evidence of traumatic cataract) was observed in 19 animals (11 unilateral and 8 bilateral cases) representing a frequency of 11.05% (95% CI: 6.78 – 16.71%). The mean pachymetry, axial length, and spherical equivalent were, respectively, 474.43±32.21 mm (median: 473.00), 19.49±1.24 mm (median: 19.46), and 0.30±1.70 D (median: 0.38). Age was significantly associated with cataract occurrence, pachymetry, axial length and spherical equivalent. For each 1 year increase of age, the odds of having cataract increased by 18% (OR= 1.18; 95%CI: 1.06 – 1.31; p=0.001), the pachymetry decreased by 1.11 mm (Coef.= -1.11; 95%CI: -2.00 to -0.23; p=0.013), the axial length increased by 0.03 mm (Coef.= 0.03; 95%CI: 0.01 to 0.05; p<0.001), and the spherical equivalent decreased by 0.12 D (Coef.= -0.12; 95%CI: -0.22 to -0.02; p=0.015).

Conclusions : Rhesus macaques have age-related ocular changes similar to those observed in human aging, including higher occurrence of cataract, decreasing corneal thickness, increasing axial length, and myopic shift. Our results are from a natural free-ranging population without medical intervention, which represents an excellent population for studying naturally occurring age-related eye diseases.

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