C M Dickinson¹, H J Smith¹, I Cacho¹, R A Harper²
¹UMIST, Department of Optometry and Neuroscience, Manchester, United Kingdom; ²Manchester Royal Eye Hospital, Ophthalmology, Manchester, United Kingdom
BACKGROUND
A reduction in reading acuity and speed are common and significant difficulties for low vision patients. In the presence of an intact central visual field, however, magnification increases reading speed to a normal level and fluent leisure reading is possible. If there is a central scotoma, however, it has been predicted that reading speed will inevitably be low, even if the print is magnified. This study investigated patients with age-related macular degeneration (AMD) to determine the relationship between clinical impairment measures and reading performance.
METHOD
As part of an ongoing RCT of prism spectacles, 24 AMD patients (aged 70-91 years, median age 82 years) with bilateral central scotomas were examined: median logMAR binocular VA was 0.83 (range 0.22 to 1.32) and median Pelli-Robson contrast sensitivity was 1.05 (range 0.1 to 1.35). Threshold reading acuity, critical print size (CPS) and optimum reading speed were determined using MNREAD, and the area of central scotoma and the distance of the nearest non-scotomatous region to the fixation point in the better eye, were found using the Bjerrum screen.
RESULTS
Median reading speed was 50 wpm (but with a range from 6 to 175), and the median ratio of CPS to threshold reading acuity (the acuity reserve) was 1.58:1 (with a range 1.07:1 to 5.88:1). As expected, distance acuity was strongly correlated to near acuity (r = 0.85) but less strongly to reading speed (r = -0.50). Visual field area was however not a statistically significant predictor of reading speed.
CONCLUSION
Theoretical models of reading performance with a central scotoma may give a useful guide to average performance, but clinicians need to be aware of considerable inter-subject variability when applying such guidelines to individual patients.
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