Comparative Analysis of Unaided Emmetropic and Unaided Noncorrected Myopic Underwater Visual Acuity

Abstract

This study was undertaken to explore the effect of an underwater environment on unaided emmetropic and unaided noncorrected myopic visual acuity. University of Oregon men and women students (N = 60) having a swimming ability of intermediate or better volunteered for the study. A lighted Snellen letter chart was used to classify 30 subjects as emmetropes with a visual acuity of 20/20 or better and 30 subjects as myopes with a visual acuity of 20/200 or worse. Each of the 30 subjects in both classifications was randomly assigned to treatments of either bright or dim target illumination and one of three solutions (hypotonic, isotonic, and hypertonic). The measurement of unaided underwater visual acuity was determined by means of an adapted Landolt broken circle target and an instrument designed to measure the distance at which an individual can perceive the direction of the break in the circle. The results indicated that (1) myopes (20/200 or worse) can, on the average, see significantly (.055 level) better under water than emmetropes (20/20 or better), (2) variations in illumination between 1 and 2 ft-c have little effect on unaided underwater visual acuity, (3) variations in liquid mediums of hypotonic, isotonic, and hypertonic content used in this study for duration of 3 min have little effect on visual acuity, and (4) the biserial correlation between unaided atmospheric and unaided underwater visual acuity is—.258.