Estimation of Subjective Visual Acuity and Refractive Error

ABSTRACT

Estimation of subjective visual acuity depends on the test type, size of object, illumination, distance, position of eyeball and head, and shape of palpebral fissure. The purpose of this study is to observe discrepancy between the correct subjective visual acuity obtained in ideal proper condition and the subjective visual acuity obtained by any means of squeezing, turning eyeball or head in refractive errors: myopia, hyperopia and astigmatism. The results of this study were as follow: 1. Visual acuity with squeezing was better than normal visual acuity in all refractive errors. 2. Discrepancy between normal visual acuity and visual acuity with squeezing was the greatest in the myopia: Visual acuity with squeezing was the best in the myopia. Better visual acuity with squeezing was shown in the compound myopic astigmatism and next in the simple myopic astigmatism. The differance between those two kinds of visual acuities was not noticeable in the hyperopia and mixed astigmatism. 3. Discrepancy between normal visual acuity and visual acuity with squeezing was more in against-the-rule astigmatism than in with-the-rule astigmatism: Visual acuity with squeezing was better in against-the-rule astigmatism than in with-the-rule astigmatism. This study have shown that visual acuity should be measured not only in proper condition of test but also in proper position of a patient with refractive error, especially with myopia.