COMPARISON OF OBJECTIVE AND SUBJECTIVE REFRACTIONS IN MACACA MULATTA.

Chea-su Kee

Abstract

PURPOSE. Animal studies of refractive development typically determine refractive status under anesthetized conditions using objective techniques like retinoscopy. However for many reasons the refractive status determined by retinoscopy under anesthetized conditions may not match the refractive status manifest by the animal when it is awake. In this study, we compared objective and subjective measurements of the refractive status of adolescent rhesus monkeys. METHOD. The spectacle-plane refractive correction was measured by retinoscopy while the monkeys (n=4) were cyclopleged (1% Tropicamide) and anesthetized (20mg/kg ketamine; 0.2 mg/kg acepromazine). The eye’s axial dimensions were measured by A-Scan Ultrasonography. Subjective measures of refractive status, with and without cycloplegia were obtained using psychophysical methods. Specifically we measured spatial contrast sensitivity as a function of spectacle lens power. The lens power that produced the highest contrast sensitivity for relatively high spatial frequency gratings was taken as the subjective refraction. Following the behavioral experiments cycloplegic retinoscopy was done again to determine the repeatability of these measurements.

RESULTS. There was good agreement between retinoscopic measures obtained before and after the subjective refraction. Retinoscopy consistently yielded higher amounts of hyperopia relative to either of the subjective measurements and these differences decreased as a function of axial length. The average differences between the retinoscopy measurements and the subjective refractions obtained with and without cycloplegia were 2.01D and 2.13D, respectively.

CONCLUSIONS. The results show that subjective measures of refraction in behaving monkeys are less hyperopic than refraction measurements obtained by retinoscopy. The reduction of this difference as a function of axial length suggests that this discrepancy may be due in part to the small eye artifact that has been suggested to occur with retinoscopy.

Details

Year: 2001

Program Number: Poster 100

Author Affiliation: n/a

Co-Authors: Ramkumar Ramamirtham, Li-Fang Hung, Qiao Ying, Ronald Harwerth, Earl Smith III

Co-Author Affiliation: University of Houston, University of Houston

Room: Exhibit Hall C