Spontaneous refractive error, ocular biometry and age related lens changes in a population of geriatric rhesus macaques

The purpose of this investigation was to determine refractive error, ocular biometry and age-related lens changes in a population of geriatric rhesus macaques ( Macaca mulatta ) from the California National Primate Research Center (CNPRC). Ophthalmic examination was performed in 182 rhesus macaques 19 years of age using a cross-sectional study design, including streak retinoscopy, anterior segment tomography, A-scan ultrasound biometry and handheld slit lamp biomicroscopy. Median spherical equivalent refractive error was + 0.75 D with an interquartile range (IQR) of 0 to 1 D. Most eyes were hyperopic ( n  = 102, 55%) or emmetropic ( n  = 68, 36%); myopic eyes were the least common ( n  = 17, 9%). Anisometropia was present in 13 subjects (14%). Mean (± SD) corneal curvature was 52.6 ± 2.6 D ( n  = 79). Mean (± SD) axial globe length was 20.2 ± 1.5 mm, anterior chamber depth was 3.7 ± 0.4 mm, lens thickness was 4.1 ± 0.4 mm, and vitreous chamber depth was 12.2 ± 1.0 mm ( n  = 86). Median (IQR) nuclear sclerosis grade ( n  = 191, 98%) assessed with the lens opacities classification system II was 1 (1–2). Hyperopia is the most common refractive error in the geriatric rhesus macaque population at CNPRC. This study provides reference values for an isolated geriatric rhesus macaque population and broadens our understanding of refractive error and lens opacities in geriatric rhesus macaques which may serve as a model for studying novel therapeutics for refractive errors and cataracts.