UNLABELLED: Main purpose of this study was to evaluate effect of aniseikonia on the stereo vision. We had together 90 subjects without eye pathology with or without habitual correction. Five of them were excluded due to important anisometropia or bad visual acuity (V < 0.5 on worse eye). All 85 subjects every in 4 cases (without size lens, with size lens on OD 1, 3 and 5 %) undergone measuring of their stereoscopy parallax. This was evaluated by Random dot stereo test. The level for stereoscopy vision was set bellow 60 arc seconds. This criterion was not achieved naturally by 6 subjects, so final number of all cases was 316 (100 %). As a whole 48 subjects (15.2 %) fail after using the test with size lens on OD 1, 3 or 5 %. All 268 cases (84.8 %) had not impaired stereoscopy parallax with size lens over chosen critical level. KEY WORDS: size lens, anisometropia, aniseikonia, heterophoria, stereoscopy vision.