Visual performance in cataract patients with low levels of postoperative astigmatism: full correction versus spherical equivalent correction

Robert P Lehmann¹, Diane M Houtman^2
1Lehmann Eye Center, Nacogdoches, TX, ²Alcon Research Ltd, Fort Worth, TX, USA

Purpose: To evaluate whether visual performance could be improved in pseudophakic subjects by correcting low levels of postoperative astigmatism.
Methods: An exploratory, noninterventional study was conducted using subjects who had been implanted with an aspheric intraocular lens and had 0.5–0.75 diopter postoperative astigmatism. Monocular visual performance using full correction was compared with visual performance using spherical equivalent correction. Testing consisted of high- and low-contrast visual acuity, contrast sensitivity, and reading acuity and speed using the Radner Reading Charts.
Results: Thirty-eight of 40 subjects completed testing. Visual acuities at three contrast levels (100%, 25%, and 9%) were significantly better using full correction than when using spherical equivalent correction (all P < 0.001). For contrast sensitivity testing under photopic, mesopic, and mesopic with glare conditions, only one out of twelve outcomes demonstrated a significant improvement with full correction compared with spherical equivalent correction (at six cycles per degree under mesopic without glare conditions, P = 0.046). Mean reading speed was numerically faster with full correction across all print sizes, reaching statistical significance at logarithm of the reading acuity determination (logRAD) 0.2, 0.7, and 1.1 (P , 0.05). Statistically significant differences also favored full correction in logRAD score (P = 0.0376), corrected maximum reading speed (P < 0.001), and logarithm of the minimum angle of resolution/logRAD ratio (P < 0.001).
Conclusions: In this study of pseudophakic subjects with low levels of postoperative astigmatism, full correction yielded significantly better reading performance and high- and low-contrast visual acuity than spherical equivalent correction, suggesting that cataractous patients may benefit from surgical correction of low levels of preoperative corneal astigmatism.

Keywords: aspheric intraocular lens, astigmatism, cataract surgery, contrast sensitivity, reading acuity, visual acuity