Using high resolution perimetry in repeated sessions, we investigated 27 patients with homonymous visual field defects in order to detect islands of vision within the damaged area, and to determine color- and form-recognition abilities within these zones of residual vision. In most patients we found circumscribed areas within the "blind" field in which the stimulus was detected in about 50% of presentations. Only one patient had an island of vision greater than 5 degrees within the defective area. We also found an area of variable performance between the blind and the intact field. Borders of field defects were classified as being: (a) sharp (small transition zone), (b) medium, or (c) fuzzy (scattered deficits). We propose that transition zones are functional representations of partially spared neuronal structures in areas of the brain which are only partially injured.