Crowding in visually impaired patients: contour interaction and/or gaze-selection defects?

Visual crowding, defined as a lower line acuity compared to single-letter acuity, was investigated in 18 visually impaired patients. The separate effects of contour interactions and gaze-selection defects were investigated using a line-acuity test, a single-letter acuity test, and the Regan repeat-letter test. The limits of normality were established from data collected on 25 age-matched normals. In the visually impaired group, 83% of the patients showed visual crowding. When dividing the group into the other two categories, 39% of patients showed gaze-selection problems and 56% demonstrated abnormal contour interactions. Only 5% of the patients showed no effect of contour interactions or gaze-selection defect. These results have important implications for the visual rehabilitation of such patients.