Few studies have specifically investigated the functional effects of uncorrected astigmatism on measures of reading fluency. This information is important to provide evidence for the development of clinical guidelines for the correction of astigmatism.
Participants included 30 visually normal, young adults (mean age, 21.7 ± 3.4 years). Distance and near visual acuity and reading fluency were assessed with optimal spectacle correction (baseline) and for two levels of astigmatism, 1.00 diopter cylinder (DC) and 2.00 DC, at two axes (90 and 180°) to induce both against-the-rule (ATR) and with-the-rule (WTR) astigmatism. Reading and eye movement fluency were assessed using standardized clinical measures including the test of Discrete Reading Rate (DRR), the Developmental Eye Movement test (DEM), and by recording eye movement patterns with the Visagraph (III) during reading for comprehension.
Both distance and near acuity were significantly decreased compared with baseline for all the astigmatic lens conditions (p < 0.001). Reading speed with the DRR for N16 print size was significantly reduced for the 2.00 DC ATR condition (a reduction of 10%), whereas for smaller text sizes, reading speed was reduced by up to 24% for the 1.00 DC ATR and 2.00 DC condition in both axis directions (p < 0.05). For the DEM, subtest completion speeds were significantly impaired, with the 2.00 DC condition affecting both vertical and horizontal times and the 1.00 DC ATR condition affecting only horizontal times (p < 0.05). Visagraph reading eye movements were not significantly affected by the induced astigmatism.
Induced astigmatism impaired performance on selected tests of reading fluency, with ATR astigmatism having significantly greater effects on performance than did WTR, even for relatively small amounts of astigmatic blur of 1.00 DC. These findings have implications for the minimal prescribing criteria for astigmatic refractive errors.