Alexia and quadrant-amblyopia: reading disability after a minor visual field deficit.
Reading difficulties caused by hemianopia are well described. We present a study of alexia in a patient (NT) with a milder visual field deficit. The patient had suffered a cerebral haemorrhage causing damage to the left occipital cortex and underlying white matter. NT's text reading was slow and prone to error, but recognition of single letters was preserved. Single word reading was accurate, but slower than normal. On perimetric testing NT initially showed an upper right quadrantanopia, but by attending covertly to this quadrant he could achieve luminance detection except in a small scotoma above the reading line. A whole report experiment showed that letter perception was severely compromised in the quadrant, consistent with cerebral amblyopia. On follow-up testing one and a half year post stroke, a clear spontaneous recovery had occurred, reflected in improved text reading with close to normal eye movements. Still, subtle reading difficulties and oculo-motor abnormalities remained. Overall, the study shows how amblyopia in one quadrant can lead to a characteristic form of alexia.
Habekost
Thomas
T
Center for Visual Cognition, Department of Psychology, University of Copenhagen, Linnesgade 22, 1361 Copenhagen K, Denmark. Thomas.Habekost@psy.ku.dk
Starrfelt
Randi
R
D000328:Adult; D000550:Amblyopia / Q000150:complications* / Q000473:pathology / Q000503:physiopathology; D004411:Dyslexia, Acquired / Q000209:etiology* / Q000473:pathology; D005133:Eye Movements; D005500:Follow-Up Studies; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D009483:Neuropsychological Tests / Q000706:statistics & numerical data; D010775:Photic Stimulation / Q000379:methods; D011930:Reaction Time / Q000502:physiology; D011932:Reading; D014794:Visual Fields / Q000502:physiology*