A comparative study of stereoacuity in against the rule and oblique astigmatism.

Abstract

OBJECTIVE: To measure and compare the stereopsis level among the persons with against-the-rule and oblique astigmatism using Lang I and Lang II tests.

METHODS: Informed consent was obtained from each patient both in verbal and written form. A proforma was filled at the time of examination. Visual acuity was checked on Snellen chart which was then converted to log MAR values. The type and amount of astigmatism was measured by performing refraction subjectively using trial lenses. Individuals having cylindrical value at the axis of 70-120 degrees were considered to have against-the-rule astigmatism while individuals having cylindrical value at the axis of 20-60 degrees and 130-160 degrees were considered to have oblique astigmatism. Lang I and Lang II are performed for detailed or fine measurement of stereopsis. The sample size was 36 with a confidence level of 95% is taken and the study is conducted in the College of Ophthalmology and Allied Vision Sciences (COAVS), LAHORE. Data was entered and analyzed using a statistical package for social sciences (SPSS version-25.00). Mann-Whitney test was applied to compare the results. P-value ≤0.05 was considered significant.

RESULTS: A total of 36 individuals were included in this study and out of 36 individuals 18 individuals had against-the-rule astigmatism and remaining 18 had oblique astigmatism. Stereoacuity was measured in these two groups of astigmatism. Subjective refraction showed that the visual acuity of most of the individuals in right eye was equal to 6/36 and in left eye 6/24. And a greater number of individuals had plano spherical power in both eyes and cylindrical power of -0.50 DC in both eyes. The p-value of visual acuity, spherical readings, cylindrical readings showed that these all were insignificant in our results as p-value is >0.05. The results of Lang I test showed that large number of individuals (52.8%) did not respond to this test while Lang II test showed that (41.67%) individuals did not respond to this test means the stereopsis was absent in them. Shapiro Wilk test was used to check the normality of data and according to this test the p-value is ≤0.05 (p<0.01). It means that our data is not showing normality therefore we apply non-parametric tests. Then the p-values were find using Mann Whitney test (non-parametric test). And it showed that the p-value in Lang I test is (p=0.006) is ≤0.05. Similarly, the p-value for Lang II is (p=0.034) is also ≤0.05. As the p-values in Lang I and Lang II are ≤0.05 it means that the results are significant for this study.

CONCLUSION: Oblique astigmatic individuals had significantly poor stereopsis as compared to against-the-rule astigmatic individuals
using Lang I and Lang II tests.

KEYWORDS: Astigmatism, Against the rule astigmatism, Oblique astigmatism, Stereopsis, Stereoacuity, Lang I, Lang II, Visual acuity.