IMPROVEMENT IN VERNIER ACUITY IN ADULTS WITH AMBLYOPIA - PRACTICE MAKES BETTER

Purpose. To determine the nature and limits of visual improvement thro ugh repetitive practice in human adults with naturally occurring ambly opia. Methods. A key measure the authors used was a psychophysical est imate of Vernier acuity; persons with amblyopia have marked deficits i n Vernier acuity that are highly correlated with their loss of Snellen acuity. The experiment consisted of three phases: pretraining measure ments of Vernier acuity and a second task (either line-detection thres holds or Snellen acuity) in each eye with the lines at two orientation s; a training phase in which observers repetitively trained on the Ver nier task at a specific line orientation until each had completed 4000 to 5000 trials; and posttraining measurements (identical to those in the first phase). Two groups of amblyopic observers were tested: notic e observers (n = 6), who had no experience in making psychophysical ju dgments with their amblyopic eyes, and experienced observers (n = 5), who had previous experience in making Vernier judgments with their amb lyopic eyes (with the lines at a different orientation) using the sign al-detection methodology. Results. The authors found that strong and s ignificant improvement in Vernier acuity occurs in the trained orienta tion in all observers. Learning was generally strongest at the trained orientation but may partially have been transfer red to other orienta tions (n = 4). Significant learning was transferred partially to the o ther eye (at the trained orientation) in two observers with anisometro pic amblyopia. Improvement in Vernier acuity did not transfer to an un trained detection task. In two observers, the improvement in Vernier a cuity was accompanied by a commensurate improvement in Snellen acuity. Conclusions. Some adults with amblyopia retain a significant degree o f neural plasticity. Although several observers (primarily novices) sh owed evidence of generalized learning, several amblyopic patients show ed evidence for improvement that was orientation and task specific. In this latter group of observers, the improvement appeared to reflect a lterations that were, at least in part, in early neural processes that were orientation specific and were localized beyond the site of conve rgence of the two eyes.