Visual function, visual attention, and mobility performance in low vision.

PURPOSE: The aim of this study was to determine if useful field of view (UFV) measures help to predict aspects of orientation and mobility in people with visual impairment. The UFV is a composite measure of visual attention, ability to detect objects in the presence of clutter and basic visual functions such as visual field loss and contrast sensitivity.

METHODS: Thirty-five participants aged 20 to 80 years with low vision due to a variety of visual disorders took part. Mobility around a partly indoor and exterior real-life mobility course was measured, together with UFV and clinical measures of contrast sensitivity (CS), visual fields, and visual acuity. Two series of models were considered; series 1 using the UFV scores as measured and series 2 using the UFV scores corrected for visual field loss (only counting errors in areas of intact visual field).

RESULTS: UFV was found to be an important predictor of some aspects of mobility performance. Mobility errors were best predicted by uncorrected UFV (R = 0.38), although CS was also a good predictor. Walking speed and preferred walking speed (PWS) were best predicted by uncorrected UFV and age (R = 0.575 and 0.573, respectively). The visual detection distance and visual identification distances were best predicted by clinical vision measures, such as contrast sensitivity, visual fields, and central vision function. The percent PWS was not predicted by any of the measures we used. None of these models was improved by the addition of the corrected UFV scores.

CONCLUSIONS: These results indicate that attention and the presence of distractors, as well as visual function and age, are important factors in orientation and mobility performance, in particular mobility errors, walking speed and PWS.