Reading with a macular scotoma. II. Retinal locus for scanning text.

To elucidate how patients with macular scotomas use residual functional retina for inspecting visual detail and reading, we tested three patients with dense macular scotomas using a scanning laser ophthalmoscope that allows an examiner to view and record stimuli on the retina while the patient views them. Using standard psychophysical techniques, we determined the retinal position of scotomas, the retinal areas used for fixating and inspecting acuity targets, and the retinal area used for reading simple, three-letter, nonsense syllables. We found that each patient used a single, idiosyncratic retinal area, immediately adjacent to the scotoma, for fixating, inspecting acuity targets, and scanning simple, nonsense-syllable text. This preferred retinal locus (PRL) was at different retinal eccentricities (relative to the foveola) for each patient and was not always as close as possible to the foveola. There appears to be no simple rule by which patients "select" a particular PRL. Plots of text placement on the retina revealed considerable differences in patients' abilities to execute an orderly text scan. Two patients read text more rapidly with a novel retinal area than with their PRL, suggesting that the PRL may not be optimal for text reading.