Comparison of Crowding Bar and Linear Optotype Acuity in Amblyopia

A series of preferred and amblyopic eyes of fifty-one children were examined by masked examiners to compare the results of testing vision with linear symbols versus isolated symbols surrounded by crowding bars. Data were obtained with a new instrument, the B-VAT™ II Video Acuity Tester. Group 1 (24 patients) data were used to compare linear acuities with acuities obtained with crowding bars at one stroke width (one-fifth letter) separation. A significant difference between linear and crowded acuity was found for both amblyopic and preferred eyes, with crowded acuity approximately one line worse. Group 2 (27 patients) data were used to compare linear acuities with acuities obtained with crowding bars at 2.5 stroke width (half letter) separation. There was no significant difference between linear and crowded acuity in the amblyopic eyes. Preferred eyes had a slight but significant difference of .29 lines. These results suggest that crowded acuity with 2.5 stroke width (half letter) separation may provide a good approximation to linear acuity in young amblyopic patients.