Reading disorders due to visual field defects: a neuro-ophthalmological view

Abstract

Background: Reading disorders can be caused by visual field defects. Analysis of the reading process provides important information about perceptual preconditions and cortical adaptive strategies, which are also of significance for rehabilitation. Methods: Reading performance was examined using a scanning laser ophthalmoscope (SLO), which allows the simultaneous assessment of the preferred retinal locus (PRL) in relation to the stimuli and the eye movements. Visual fields were measured using Tuebingen perimetry and a self-developed SLO perimetry, attentional fields using the Test of Sustained Attention. Results: Patients with absolute central scotomas are only able to read if they learn to use an eccentric PRL. With a ring scotoma, reading ability depends on the size of the intact central island and the fixation behavior.With hemianopia, it is crucial whether there is macular splitting or sparing. Without sparing, reading performance depends on adaptive strategies such as predictive saccades or eccentric fixation.The latter causes a shift of the field border towards the hemianopic side in conventional perimetry. Locations of high attentional capability during central fixation (early stage of maculopathy) correspond to the later eccentric PRL during follow-up. Conclusions: Reading performance depends on the size of the perceptual area and the resolution of the PRL used for reading. Compensating strategies are crucial for regaining reading ability. Eccentric fixation causes a shift of the sensory and oculomotor reference, indicating high cortical plasticity. There is evidence that the location of a future PRL is influenced by sustained attention – a mechanism that could be utilized for specific training. Reading disorders are strongly connected with neuro-ophthalmological issues.