Comparison of stereopsis and contrast sensitivity in myopic and hyperopic anisometropia.

BACKGROUND: Good vision has always been important for mankind; ancient activities like hunting and fishing require the same eye quality as driving a car or flying an airplane. A significant loss of vision occurs resulting in a poor quality of life. If there is difference of more than 2D in the total refractive power of both eyes considered as anisometropia. Anisometropia results in aniseikonia which causes disturbance in the fusion of slightly two different images seen by each eye. As fusion is disturbed, stereopsis (depth perception) is also disturbed. To asses functional vision contrast sensitivity function can be a helpful tool especially when careful evaluation is essential other than specified by visual acuity. OBJECTIVE: To compare stereopsis and contrast sensitivity in myopic and hyperopic anisometropia and evaluate any difference in contrast sensitivity and stereopsis in different degrees of myopic and hyperopic anisometropic correction. PATIENTS AND METHOD: A comparative cross-sectional study was conducted on 31 patients having different degree of myopic and hyperopic anisometropia and its influence on contrast sensitivity and stereopsis. Distance (6m) and near (33 cm) visual acuity was measured by using Snellen distance and near visual acuity chart and contrast sensitivity was measured by using Pelli Robson contrast sensitivity chart. Stereopsis was measured by Lang1, Lang2 and Frisby. Results were obtained by asking the patient to fill a structured Performa. RESULT: Contrast sensitivity was affected more in hyperopic anisometropic patients than in myopic anisometropia patients. Mild and moderate myopic patients showed normal contrast sensitivity while severe myopes have reduced contrast sensitivity. Hyperopes have reduced contrast sensitivity as compared to myopes. Moreover, binocular contrast was better than monocular contrast. By comparing pre and post examination results of anisometropic patients showed that there was significant improvement in stereopsis (depth perception) at Lang1 test, Lang2 test and at Frisby test in anisometropes. CONCLUSION: It was concluded that myopic and hyperopic anisometropes show reduced contrast as compared with emmetropes. Mild and moderate anisometropes have significant contrast with and without optical correction. Severe anisometropes have insignificant contrast sensitivity visual function without optical correction which can be improved by wearing optical correction. Binocular contrast was better than monocular contrast sensitivity. Stereopsis in isoametropes was better than anisometropes. Stereopsis decreased as degree of anisometropia increased.