QUANTIFICATION OF PRISM INDUCED METAMORPHOPSIA AS A MODEL FOR CLINICAL RETINAL (AND OTHER) DISTORTIONS

Metamorphopsia (all causes) results in perceived distortions in the vi sual field. A simple technique utilizing hyperacuity judgements was de veloped in this laboratory some years ago to allow quantification of s uch distortions. We ask here, how good is this assessment method at de tecting a distortion? To control better investigations of metamorphops ia, a model providing constant optical distortions and resultant perce ptual metamorphopsia was devised using plane prisms of 8 Delta and 15 Delta. The instrument includes a beamsplitter and a CRT display contro lled by an IBM PC computer and a 'mouse'. In this study, three short v ertical lines (perpendicular to the prism base-apex line) were used to assess image distortion in the central retinal area. Positions of ind ividual lines of this pattern were varied in order to determine percei ved distortions induced by a prism. Normal observers were tested on mu ltiple occasions. It is possible to measure accurately prism-induced d irectional biases (mean locations) using this method. We separated per sonal setting biases from the prism-related distortions. The test meth od devised mimics modest clinical metamorphopsia. Prism magnitude affe cted settings. We were able to make judgements to less than +/-2% erro r. (C) 1997 The College of Optometrists.