PURPOSE: To evaluate the degree of metamorphopsia in 42 patients before and 6 months after vitrectomy for idiopathic unilateral macular hole. METHODS: Semicircular test and reference stimuli of variable diameters were applied in a binocular test that measured interocular size disparity in patients with unilateral macular hole. The test was applied 1 day before surgery and repeated after 6 months. RESULTS: Before surgery, mean disparity was 0.34 degrees at 1 degrees visual field eccentricity declining to a plateau value of approximately 0.2 degrees between 3 degrees and 5 degrees of eccentricity. Six months after successful hole closure, interocular disparity was practically constant, with a median disparity below 0.1 and no significant effect of eccentricity. Baseline interocular disparities lower than 0.35 degrees at 1 degrees eccentricity were associated with nine EDTRS letters of better visual outcome compared with higher disparities (P < 0.001). CONCLUSIONS: Metamorphopsia was consistently reduced after macular hole surgery, supporting that the intervention was successful in repositioning displaced photoreceptors toward their original location. Final best corrected visual acuity was related to the degree of preoperative disparity in spatial projection between receptive units with a shared perceptual projection in visual space in the two eyes. (ClinicalTrials.gov number, NCT00302328.).