The Visual Acuity of Partially Sighted Persons

The visual acuity of partially sighted patients, as measured by letter recognition, may show various phenomena which affect Its validity as a predictor of visual capacity. These include peripheral fixation, visual search, and exaggerated dependence on object luminance and contrast.In particular, the “6 metre acuity” and/or the acuity at farther distances, cannot be predicted from measurements made at shorter distances, since many patients exhibit large variations in visual acuity with viewing distance.Data on these variations will be presented, together with a theory for their occurrence. This also explains why a given degree of magnification improves the acuity of different patients by greatly differing amounts.In support of the theory, recent attempts to improve the visual acuity of selected patients with appropriate exercises, have proved highly successful.