Spontaneous variations in refractive error and axial length identified in a population of geriatric rhesus macaques

Abstract

Purpose : The purpose of this study was to determine refractive error and ocular biometry of eyes in a population of geriatric rhesus macaques (Macaca mulatta) at the California National Primate Research Center (CNPRC).

Methods : Rhesus macaques ≥ 18 years of age at the CNPRC received a comprehensive ophthalmic examination including slit lamp biomicroscopy, indirect ophthalmoscopy, streak retinoscopy, and A-scan ultrasound biometry. One-way analysis of variance was used to compare anterior chamber (AC) depth, lens thickness and vitreous length, and axial globe length, between refractive error groups (myopia, emmetropia, and hyperopia). Data are mean ± SD.

Results : Sixty-seven rhesus macaques, 43 females and 24 males, aged 18.3-29.5 years were included. Mean refractive value was 0.43 ± 1.86 D. Fifty-nine, 51 and 12 eyes were hyperopic (> +0.50 D), emmetropic (-0.50 to +0.50 D), and myopic (< -0.50 D), respectively; 12 eyes could not be measured. Two eyes showed high hyperopia (> +5.00 D), 2 showed moderate hyperopia (+2.25 to +5.00 D), 3 showed moderate myopia (-6.00 to -3.00 D), and one showed high myopia (< -6.00 D). Mean AC depth, lens thickness, vitreous length and axial globe length for emmetropes were at 3.53 ± 0.22, 4.32 ± 0.22, 11.86 ± 0.72, and 19.70 ± 0.76 mm, respectively. Axial globe length and vitreous length were significantly longer in myopes versus hyperopes at 20.52 ± 0.71 and 12.69 ± 0.70 versus 19.63 ± 0.67 and 11.73 ± 0.75 mm, respectively (P = 0.0004 and 0.0002); no significant differences were observed in AC depth or lens thickness between these 2 groups at 3.55 ± 0.31 and 4.28 ± 0.33 versus 3.56 ± 0.36 and 4.33 ± 0.33 mm, respectively (P = 0.97 and 0.90).

Conclusions : Spontaneous models of hyperopia and myopia with concurrent short and long axial globe and vitreous lengths, respectively, exist at a relatively high frequency in a colony of NHPs. The correlation between refractive errors and individual housing environmental conditions should be clarified, and genetic analyses should be performed to identify putative disease-causing mutations.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.