Macular disease produces central field loss and seriously disrupts reading performance. Training individuals with central field loss to read using eccentric retinal regions for fixation is a time-consuming and often frustrating experience. Moreover, reading performance, even after training and use of magnification devices, rarely approaches that of normally-sighted individuals. One possible reason for this is that, after central field loss, the oculomotor control system must undergo a difficult process of adaptation to permit eccentric viewing of text. Another possibility is that visual characteristics limit the ability of the peripheral retina to read. Experiment I proposes to compare reading rates in normal subjects, and changes therein with practice, using two reading-testing paradigms at each of three eccentricities. One requires only the horizontal eye movements characteristic of normal reading. Thus changes in reading rate with practice could be due to either oculomotor or sensory adaptation. The second paradigm, by completely eliminating the need for eye movements, will be used to provide an estimate of sensory limits (and adaptation). Experiments IIa-c are designed to compare central vs. peripheral retinal regions of the normal eye with respect to letter spacing (""""""""crowding""""""""), visual persistence, and spatial phase discrimination. To evaluate the significance of results obtained with normal subjects, similar measurements will be made on patients with long-standing central field loss. A Double Purkinje-image Eyetracker will be used to provide the varying degrees of retinal image stabilization required in all experiments.
| Higgins, K E; Arditi, A; Knoblauch, K (1996) Detection and identification of mirror-image letter pairs in central and peripheral vision. Vision Res 36:331-7 |
