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R Ramamirtham, A Roorda, C-S Kee, L-FF Hung, Y Qiao, EL Smith; Wave Aberrations in the Young Monkey Eye . Invest. Ophthalmol. Vis. Sci. 2002;43(13):181.
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Purpose:Animal studies on refractive error and emmetropization aim at determining the factors affecting normal and abnormal growth of the eye. The blur due to aberrations may play an important role in eye growth. However aberrations in young rhesus monkeys, animals frequently used in studies of refractive development, have not been measured. In this study, we report on the monochromatic aberrations in fifteen eyes of eight young monkeys. Methods:Eight monkeys ranging in age from 113 - 229 days were used as subjects. The animals were anesthetized with ketamine hydrochloride (20 mg/kg) and acepromazine maleate (0.2 mg/kg) and dilated with 1% tropicamide to facilitate aberration measurements. We used a headmount attached to a stage with five degrees of movement (X-Y-Z + tip-tilt) to control the animal's pupil location and fixation direction. Aberration measurements were made along the presumed line of sight, based on the Hirschberg reflex, which was continually monitored with a video camera. The tear film was maintained by frequently irrigating the eye with artificial tears. Wave aberration measurements were made with a custom-built Shack-Hartmann wavefront sensor (microlens array: 0.4 mm diameter lenslets, 24 mm focal length). Five measurements were made on each eye over a 6 mm pupil. Results:Aberration measurements were repeatable within a single, five-measurement session (0.13 microns SD in the RMS wave aberrations above second order). The aberrations between the individual eyes were variable, ranging in RMS from 0.21 to 0.99 microns with an average of 0.49 +/- 0.19 microns. The magnitude of the aberrations decreased with increasing aberration order. On average, none of the terms above the second order were significantly different from zero, including spherical aberration. Conclusion:Aberrations of young monkey eyes are similar in nature to humans. They exhibit a similar inter-individual variability and decrease in magnitude with increasing order. The magnitude of the aberration in the young monkey is about two times higher than in an adult human eye. However, the aberrations are more similar if we consider the pupil size relative to the smaller eye size of the young monkey.
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