homonymous hemianopia Scanning the visual world : a study

Objectives—This study examined the scanpaths of patients with homonymous hemianopia while viewing naturalistic pictures in their original and also spatially filtered forms. Features of their scanpaths with respect to various saccade and fixation parameters were examined to determine whether they develop compensatory eye movement strategies. The eVects of various lesion parameters including location, size, and age on the evolution of such strategies were considered. Methods—Eye movements of eight patients with homonymous hemianopia (four left, four right), but lacking neglect, were recorded while they viewed 22 images of real scenes, and they were compared with the eye movements of eight age matched controls. Subjects viewed each image for 3 seconds, initially in a spatially filtered form in which much of the semantic content had been removed, and then in their unfiltered, original form. Results—Patients diVered significantly from controls in various fixation and saccade parameters. For fixation parameters patients with hemianopia fixated diVerent spatial positions from controls, made more fixations which were more widely distributed and of shorter duration than controls, and spent a greater proportion of their total fixation time in the area corresponding to their blind hemifield. They did not make significantly more refixations than controls. For saccade parameters patients made more saccades into their blind hemifield, these saccades having shorter latencies and shorter amplitudes than those made into their seeing field, and had longer scanpaths than control subjects. The amplitude of their first saccade was longer than that of controls although its direction did not correlate simply with the side of the field defect. Their mean saccade amplitude was similar to that of controls. Filtering out high spatial frequencies within images seemed to accentuate the described diVerences between eye movement characteristics of hemianopes and controls. Scanpath diVerences correlated with increasing age but not location or size of lesions causing the hemianopia. Conclusion—Various features of scanpaths produced by hemianopes were different from normal subjects. These diVerences correlated with lesion age and may reflect the evolution of a compensatory eye movement strategy. (J Neurol Neurosurg Psychiatry 2000;69:751–759)