An eye movement study on the role of the visual field defect in pure alexia

Simulation of visual impairment in persons with normal vision for scientific research

Simulation of visual impairment in healthy eyes has multiple applications in students' training, research and product development. However, due to the absence of an existing standard protocol, the method of simulation was left to the discretion of the researcher. This review aimed to outline the various methods of simulating visual impairment and categorising them. A scoping review of the relevant publications was conducted. Of the 1593 articles originally retrieved from the databases, 103 were included in the review. The characteristics of the participants, the method for simulation of the visual impairment in persons with normal vision and the level or type of visual impairment that was simulated were extracted from the papers. None of the methods of simulation can be judged as being superior to the others. However, electronic displays produced the most consistent form of visual impairment simulation.

When mild pure alexia may not be reducible to hemianopic alexia

Individuals with pure alexia often have visual field defects such as right homonymous hemianopia. Relatively few attempts have been made to develop criteria to differentiate pure alexia from hemianopic alexia. In this Commentary we provide concrete suggestions to distinguish the two disorders. We also report on additional assessments with two previously reported cases for whom the diagnosis of pure alexia was called into question and an alternative proposal was offered that the reading deficits were instead due to hemianopia. We show that the results of clinical and neuropsychological tests do not support the account that the reading impairment was caused by the visual field defect. In particular, for both cases, the right homonymous hemianopia was not complete, and a split-field reading task demonstrated an inability also to read words presented in the intact left visual field. In conclusion, pure alexics may indeed show fairly modest word-length effects; however, the presence of right homonymous hemianopia and a non-extreme gradient of reading speed alone are not sufficient grounds to put in doubt the diagnosis. We propose that a fuller clinical and neuropsychological examination taking into account the possible confounding effects of the visual field defects will help to distinguish pure alexia from hemianopic alexia.

A formal analysis of alexia in persistent aura and a comparison to acquired pure alexia

A patient is reported with reversible pure alexia in the context of migraine with aura. Following previous, anecdotal reports, the present study is the first to formally assess word reading, writing, and other linguistic and visual processing and to compare these to a patient with stroke-related pure alexia. The reading impairment, suggestive of letter-by-letter reading, was observed across 7 days but had remitted at a 3-month follow-up. The deficit also affected recognition of letters, suggesting a functional impairment at the level of letter recognition, not just word reading. It went along with reversible abnormalities in diffusion-weighted and fluid-attenuated inversion recovery imaging in areas known to be involved in word reading.