Purpose:
To evaluate effects of astigmatism on reading acuity (RA), near visual acuity (NVA) and reading speed (RS).
Methods:
In 23 eyes of 23 subjects (26 +/-6 years) tropicamide eye drops were administered to achieve short-term cycloplegia. Using cylindrical glasses of -0.75D and -1.5D in 90° and 180° additionally to best distance correcting glasses only, influence of astigmatism on RA [logRAD], NVA [logMAR] and RS [words/min] was evaluated. Radner-Sentences and Snellen-E optotypes were displayed on a TFT-screen with the Salzburg Reading Desk, allowing for automated detection of reading distance (RD) and RS. Default RD was 40cm. Raytracing aberrometry was performed (iTrace). Differences in metrics according to orientation and magnitude of astigmatism have been tested with Wilcoxon’s-matched-pairs-test. Bland and Altman’s method was used to show general differences between RA and NVA. Multiple regression analysis was used to evaluate the influence of demographic, refractive and aberrometric status on metrics. The overall significance threshold was p=0.05.
Results:
Overall reading distance was 41.33 +/-0.27cm. No significant influence of magnitude of astigmatism on RA, NVA and RS was shown. Astigmatism with-the-rule always resulted in significantly decreased metrics compared to against-the-rule or no astigmatism. Medians and ranges were: RA90;0.75=0.68 (0.08 to 0.93), RA90;1.5=0.61 (0.19 to 0,92), RA180;0.75=0.56 (0.08 to 0.92), RA180;1.5=0.49 (0.12 to 0.87) and RA0=0.51 (-0.01 to 0.89). NVA90;0.75=0.50 (0.07 to 0.83), NVA90;1.5=0.58 (0.26 to 0.94), NVA 180;0.75=0.47 (0.06 to 0.72), NVA180;1.5=0.38 (0.19 to 0.82) and NVA0=0.50 (0.00 to 0.82). RS90=167 (45 to 299) , RS180=192 (54 to 271) and RS0=180 (89 to 339). NVA was always better than RA. Demographic, refractive and aberrometric status had no influence on any metric.
Conclusions:
Orientation of astigmatism had a significant influence on reading performance. With-the-rule astigmatism decreased parameters compared to against-the-rule and no astigmatism.
Keywords: cataract • reading • astigmatism