Eccentricity-dependent residual target detection in visual field defects

Lesions in the postgeniculate part of the visual system lead to visual field defects in the corresponding parts of the contralateral visual field. In some patients these field defects, though blind according to perimetry, have been observed to still be sensitive to visual stimulation. This report is based on studies of five such patients, whose ability to detect a small visual target presented tachistoscopically within the blind field was tested. Receiver-Operating-Characteristic curves were measured for three different retinal positions: a relatively central one, an eccentric one, and one within the natural Blind Spot that serves as a control. Results show that the four patients who could detect the target did so exclusively at the eccentric position.