Abstract
Abstract: :
Purpose: To measure horizontal and vertical aniseikonia in patients with unilateral macular epiretinal membranes (ERM). Methods: Using a modified version of the New Aniseikonia Test described by Awaya et. al. in 1982 (Nippon Ganka Gakkai Zasshi, 86(2): 217–22) horizontal and vertical aniseikonia was measured in 10 patients (aged 61–84 years) with unilateral macular ERM. 10 individuals (aged 20–55 years) with no previous ocular history and less than 1D anisometropia were assessed for horizontal and vertical aniseikonia on 2 occassions with a 2–week interval. This test–retest method allowed us to evaluate the reproducibility of our measurements (test reliability) by calculating the change in the mean, typical error, coefficient of variation (CV) and intraclass coefficient of correlation (ICC). In addition, aniseikonia was induced in 10 normal subjects (aged 32–55 years) by simulating anisometropia by means of convergent spherical lenses (+1 to +5 D). By comparing the known induced magnification with our measurements, the validity of test was studied. The y–axis intercept, slope and correlation coefficient of the best fit linear linear regression line were calculated. Results: Horizontal and vertical aniseikonia was measured in all 10 patients ranging from 4% to 14%. In 8 patients the image perceived by the affected eye was larger (macropsia) and in the remaining 2 smaller (micropsia) than in the fellow eye. In normal individuals the mean (+SD) horizontal and vertical aniseikonia was 0.8 (+0.9)% and 0.3 (+0.7)%, respectively. With the test–retest method of reliability the following figures were obtained for horizontal [change in mean 0.03 (p>0.2), typical error 0.1, CV 0.3% and ICC 0,7] and vertical [change in mean 0.3 (p>0.2), typical error 0.3, CV 2.6%]. When assessing test validity, the best fit linear regression line of horizontal aniseikonia induced by image magnificiation with plus lenses demonstrated a y–axis intercept of 0.12%, which represents the "inherent" aniseikonia in normal subjects; average slope 0.82, suggesting there is a small understimation. The correlation coefficient was 0.9%. Conclusions: Aniseikonia can be one of the factors causing visual symptoms in patients with unilateral macular ERM. The test used in our study measures aniseikonia in a reliable manner with horizontal measurements being more accurate than in the vertical direction.There may be a minor understimation. Identified symptomatic patients with aniseikonia could then be prescribed iseikonic lenses to improve their symptoms.
Keywords: clinical research methodology • macula/fovea • retina