About the role of visual field defects in pure alexia.

Abstract

Pure alexia is an acquired reading disorder characterized by a disproportionate prolongation of reading time as a function of word length. Although the vast majority of cases reported in the literature show a right-sided visual defect, little is known about the contribution of this low-level visual impairment to their reading difficulties. The present study was aimed at investigating this issue by comparing eye movement patterns during text reading in six patients with pure alexia with those of six patients with hemianopic dyslexia showing similar right-sided visual field defects. We found that the role of the field defect in the reading difficulties of pure alexics was highly deficit-specific. While the amplitude of rightward saccades during text reading seems largely determined by the restricted visual field, other visuo-motor impairments-particularly the pronounced increases in fixation frequency and viewing time as a function of word length-may have little to do with their visual field defect. In addition, subtracting the lesions of the hemianopic dyslexics from those found in pure alexics revealed the largest group differences in posterior parts of the left fusiform gyrus, occipito-temporal sulcus and inferior temporal gyrus. These regions included the coordinate assigned to the centre of the visual word form area in healthy adults, which provides further evidence for a relation between pure alexia and a damaged visual word form area. Finally, we propose a list of three criteria that may improve the differential diagnosis of pure alexia and allow appropriate therapy recommendations.

• Authors: Tobias Pflugshaupt, Klemens Gutbrod, Pascal Wurtz, Roman von Wartburg, Thomas Nyffeler, Bianca de Haan, Hans-Otto Karnath, René M Mueri
• Journal: Brain : a journal of neurology (Brain) Vol. 132 Issue Pt 7 Pg. 1907-17 (Jul 2009) ISSN: 1460-2156 [Electronic] England
• PMID: 19498088 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Topics

• Adolescent
• Adult
• Aged
• Alexia, Pure (complications, pathology, physiopathology)
• Brain (pathology)
• Brain Damage, Chronic (complications, pathology)
• Comprehension
• Dyslexia (physiopathology)
• Eye Movement Measurements
• Female
• Fixation, Ocular
• Humans
• Magnetic Resonance Imaging
• Male
• Middle Aged
• Prospective Studies
• Psychomotor Performance
• Reading
• Saccades
• Time Factors
• Vision Disorders (etiology, physiopathology)
• Visual Fields