Method for identifying amblyopes whose reduced line acuity is caused by defective selection and/or control of gaze

Three visual tests were administered to a group of 15 amblyopic children, 15 adult amblyopes and two age-matched control groups, each of 20 subjects. Test results comprised visual acuity for recognizing high contrast letters presented in line (i.e. Snellen) format, isolated-letter format and repeat-letter format. The classical Snellen format confounds the effects of gaze control defects with the effects of adjacent contours on a patient's ability to recognize a foveated letter. We designed a repeat-letter format intended to unconfound these effects. The repeat letter format is much less sensitive to gaze control defects, and somewhat more sensitive to adjacent contour interactions than is the Snellen format. We report that amblyopic eyes can be subdivided empirically into three repeat-letter categories: repeat-letter acuity significantly better than Snellen acuity; repeat letter acuity not significantly different from Snellen acuity; and repeat letter acuity significantly worse than Snellen acuity. We report that this subdivision cuts across the clinical subclassification of amblyopia and also across the crowding/no crowding subclassification. We suggest that, rather than abnormal lateral interactions, defective selection and/or control of gaze is an important factor in depressed visual acuity in amblyopic eyes of the first repeat-letter category but not for the third type, in which abnormal lateral interactions may be important. To test the hypothesis that the response to patching and refractive therapy may be less satisfactory in our first category of amblyopic eyes, we are carrying out a prospective study.(ABSTRACT TRUNCATED AT 250 WORDS)