Prevalence of astigmatism in infant monkeys

PURPOSE Human infants exhibit a high prevalence of astigmatism. Although macaque monkeys are commonly used as animal models in experiments on early ocular growth and emmetropization, the prevalence of astigmatism in infant monkeys is unexplored. In this study we examine the prevalence and nature of astigmatism in infant monkeys. METHODS Refractive and corneal astigmatism were measured in 132, 2-5-week-old rhesus monkeys (Macaca mulatta) using cycloplegic retinoscopy and keratometry, respectively. Longitudinal measures of refractive development were obtained from 16 normal infants over the first 6 months of life. RESULTS Infant monkeys exhibited a low prevalence of astigmatism. Approximately 90% of the 2-5-week-old infants had <1.00 D of either refractive or corneal astigmatism. When refractive astigmatism was observed, it was well correlated with the direction and magnitude of corneal astigmatism. When corneal astigmatism was >1.00 D (n=20), it was predominantly against-the-rule in nature (70.0%). The infant monkeys that were followed longitudinally rarely showed significant astigmatic errors at any time during the observation period. When these infant monkeys exhibited significant astigmatism, it was usually transient and not present on subsequent measurements. CONCLUSIONS Unlike human infants, infant monkeys exhibit relatively little astigmatism. The low prevalence of astigmatism during early development suggests that astigmatism does not provide an essential cue for vision-dependent eye growth in infant primates.