Purpose: To quantify, account for, and enhance the reading speed of patients with generalized retinal degeneration and small central visual fields.
Methods: Thirty-three patients with retinitis pigmentosa or choroideremia and 12 normal controls participated in the study. The patients had visual acuities of 20/200 or better, central visual field diameters of < or =20 degrees, and log10 contrast sensitivities of < or =1.65. Reading speed was measured by having participants silently read timed sentences presented with differing font size, font type (Times vs. Courier), and text polarity (standard black text on a white background vs. reversed white text on a black background) and then recall that text aloud.
Results: The patients' mean reading speed for standard polarity text using the Times font and their optimal font size was 43% of normal (P < 0.001). Patient reading speed was significantly related to visual acuity (r = 0.44; P < 0.001) and to contrast sensitivity (r = 0.68; P < 0.001) but not to central visual field diameter. In a multiple regression model, only contrast sensitivity by itself was a strong independent predictor of patient reading speed, although visual acuity and visual field in combination did nearly as well. On average, the patients read significantly faster with the Times font than with the Courier font (P < 0.001). The percentage improvement in reading speed with reverse polarity text was most related to contrast sensitivity (r = 0.47; P < 0.001), and 83% of patients with log10 contrast sensitivity of <1.0 versus 36% with higher contrast sensitivity read faster with reverse polarity text (P = 0.02).
Conclusion: Patients with retinitis pigmentosa or choroideremia and small central fields have, on average, impaired reading speed associated primarily with reduced contrast sensitivity, and those with very poor contrast sensitivity will most likely benefit from reversing text polarity.