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R. Ramamirtham, C.–S. Kee, Y. Qiao–Grider, L.–F. Hung, M. Ward, E.L. Smith, III; Corneal and Internal Wave Aberrations in Normal Rhesus Monkeys (Macaca Mulatta) . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1972.
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Purpose: Recent studies in humans have shown that aberrations produced by the anterior corneal surface are partially counterbalanced by aberrations of the internal optics of the eye. It has been suggested that this balance in aberrations may be actively regulated. As a first step in testing this hypothesis, we compared the aberrations due to the anterior cornea and the internal optics in the eyes of normal monkeys. Methods: Our subjects were 6 normal adolescent rhesus monkeys (ages 2.1 to 5.2 years). The subjects were anesthetized and cyclopleged to facilitate all measurements. Wave aberrations for the whole eye were measured using a Shack–Hartmann wavefront sensor. Aberrations of the anterior corneal surface were calculated using the corneal elevation data obtained via photokeratoscopy (EyeSys 2000) using specialized software (VOL–CT Ver 6.33). After taking into account the position of the corneal apex with respect to the pupillary axis, the internal eye aberrations for a 5 mm pupil size were estimated by subtracting the Zernike aberration coefficients for the cornea from their corresponding aberration coefficients for the whole eye. Results: For all 6 monkeys, the high order aberrations of the whole eye were smaller in magnitude than those for either the cornea or the internal optics of the eye. The average RMS errors (3rd to 10th order) for the whole eye, anterior cornea and internal optics were (right eye; mean ± 1SD) 0.16 ± 0.04 µm, 0.37 ± 0.08 µm and 0.40 ± 0.10 µm respectively. Positive spherical aberration was the largest anterior corneal aberration (+0.29 ± 0.05 µm) and was almost completely negated by negative spherical aberration (–0.28 ± 0.06 µm) of the internal optics. Conclusions: In normal monkeys, as in humans, the degree of high order aberrations is substantially less than the aberrations due to either the cornea or the eye’s internal optics. These results indicate that aberration from the anterior corneal surface and the internal optics, particularly spherical aberration, normally compensate for each other resulting in improved overall retinal image quality.
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