Effect of induced anisometropia on stereopsis and surgical tasks in a simulated environment

PURPOSE: To quantitatively correlate the loss of stereopsis by induced anisometropia with its effect on tasks that require binocular vision and stereopsis, such as ophthalmic surgery in a simulated environment. METHODS: Thirty-nine ophthalmic residents with best-corrected visual acuity of 20/20 or better OU, with normal binocular vision and stereopsis, were recruited for the study. Anisometropia was induced using spherical and cylindrical trial lenses from +1D to +5D in a trial frame. The residents performed an anterior chamber navigation exercise on the EYESi simulator and the surgical score at baseline and for each level of induced anisometropia was noted. Near stereopsis was assessed by the Randot test and TNO test at baseline and for each level of induced anisometropia. RESULTS: Stereoacuity on the Randot test and TNO test were 30 (95% CI, 25.9–34.1) and 44.4 (95% CI, 28.5–60.3) arcseconds, respectively which reduced to 65.5 (95% CI, 48.7–82.3) and 75.9 (95% CI, 15.5–136.3) arcseconds at anisometropia of +1D Sph (P < 0.001) and 380 (95% CI, 309.9–450.1) and 1922.1 (95% CI, 1582.5–2261.7) arcseconds for +5D Sph, respectively for the two tests, (P < 0.001). The corresponding surgical score reduced from 93.8 (95% CI, 91.1–96.7) to 87.5 (95% CI, 79.2–95.8, P < 0.001) for 1 DSph and 55.97 (95% CI, 38.3–73.7, P < 0.001) for 5DSph. There was a strong negative correlation between stereopsis scores and surgical task scores (Spearman's rho -0.86, P value <0.001) Similar changes were seen for anisometropia induced with cylindrical powers. CONCLUSION: Induced anisometropia is associated with a significant diminution in surgical task scores in a simulated environment and this is correlated with the deterioration in stereoacuity. Assessment of stereopsis may be included as a regular part of the screening procedure for ophthalmic trainee residents.