Residual Astigmatism Following Toric Intraocular Lens Implantation Related to Pupil Size

PURPOSE: To present two patients with residual astigmatism following toric intraocular lens (IOL) implantation. METHODS: Case reports. RESULTS: A 58-year-old woman underwent toric IOL implantation (spherical power 29.50 diopters [D], cylinder power 3.00 D; SN60T5, Alcon Laboratories Inc) to correct 2.33 D @ 80° of corneal astigmatism. Postoperatively, uncorrected distance visual acuity (UDVA) was 20/30 and corrected distance visual acuity (CDVA) was 20/22 (0 -1.75 × 95), indicating an overcorrection of astigmatism. Slit-lamp examination demonstrated no IOL misalignment. Wavefront aberrometry showed a large pupil diameter (>6 mm) and a lower corneal astigmatism in a 6-mm zone (-1.40 D @ 174°) compared to a 4-mm zone (-2.21 D @ 171°). The second patient, a 60-year-old man, underwent multifocal toric IOL implantation (spherical power 22.50 D, cylinder power 2.25 D; SND1T4, Alcon Laboratories Inc) to correct 1.51 D @ 173° of corneal astigmatism. Postoperatively, UDVA was 20/50 and CDVA was 20/20 (+0.25 -1.00 × 102), indicating an undercorrection of astigmatism. Slit-lamp examination showed no misalignment. CONCLUSIONS: Both cases indicate that unexplained residual astigmatism following toric IOL implantation may be the result of multiple factors: the effect of the spherical power and anterior chamber depth on toric IOL calculations, the effect of posterior corneal astigmatism, and the effect of a large pupil size. The first two issues may be compensated for by improving toric IOL calculations. The latter indicates that pupillometry is indicated in relatively young patients who undergo toric IOL implantation.