Reading with Visual Field Defects

Abstract

The influence of different visual field defects on the reading performance was examined with potential adaptive strategies to improve the reading process in mind. By means of an SLO, the retinal fixation locus (RFL) was determined with the use of single targets and text, and eye movements scanning the text were recorded on video tape. Additionally, eye movements were monitored by an Infrared Limbus Tracker. Visual fields were assessed by the Tübingen Manual and/or automatic perimetry. Normal subjects, and patients with central scotomata, ring scotomata, and hemianopic field defects (HFD) were examined. The main pathological reading parameters were an increase of saccade frequency and regressions per line, and a decrease of reading speed. In patients with field defects involving the visual field centre, fixation behaviour is significant for regaining reading ability. In absolute central scotoma, the lost foveal function promotes eccentric fixation. The remaining problem is insufficient resolution of the RFL, which can be compensated for by magnification of the text. In patients with insufficient size of their reading visual field, due to HFD and ring scotoma, it is crucial that they learn to use a new RFL despite intact foveolar function. Preconditions for reading have been found to be: (1) sufficient resolution of the RFL, (2) a reading visual field of a minimum extent, and (3) intact basic oculomotor function. In patients with visual field defects involving the centre, a sensory-motor adaptation process is required: the use of a new RFL as the new centre of the visual field and as the new zero point for eye-movement coordinates.