Normative Data and Effects of Refractive Status and Correction Tyle on the 40cm Longitudinal Horopter

Abstract

Abstract: : Purpose: This study investigates the variation in horopter data for a study group (n=99) based on refractive status (myopic n=60, hyperopic n=3, astigmatic n=14, emmetropic n=22) and type of correction used (spectacle n=28 or contact lens n=49) for a group of young healthy adults (21 to 31 years)with normal binocular vision. Methods: Subjects were asked to align test rods in an Apparent Frontoparallel Plane (AFPP) horopter device. Three trials were taken and averaged for each subject at a fixation distance of 40cm while wearing correction. To avoid effects of visual fatigue short periods of rest were given as needed for each subject. To compare H and R₀ values on the basis of refractive status and type of correction paired-sample T-tests (two-tailed) were performed. Results: R₀ and H values were calculated as described by Ogle (J.O.S.A. Vol 22, 1932, 538 631). For the study group, the 40 cm analytical plot was obtained by plotting R against tan alpha2. The equation defined was R= 0.995 -3.1042 tan alpha2 (H= -3.1042 and R₀= 0.995). T-tests were performed to compare differences in H and R₀ coefficient values between different types refractive states. No significance was found between emmetropes and hyperopic, myopic and astigmatic errors. Similar results were observed when comparing refractive error types with each other. T-tests also compared high (≷6D), moderate (4D-6D), and low (<4D) degrees of refractive error. Again, no significant difference was found between groups. Comparison between spectacle and contact lens correction was performed with T-tests. No significant difference was observed at the alpha level of (p<.05). Conclusion: Refractive error type and correction appear to have no impact on the 40cm fixation distance longitudinal horopter. This indicates that error type and correction do not alter the uniform and non-uniform relative magnification. Perceptually these two factors seem to have no effect on the corrected ammetrope. These results could be due to the unequal distribution of refractive error types in our sample.

Keywords: 329 binocular vision/stereopsis • 519 physiological optics