Effect of effective lens position on cylinder power of toric intraocular lenses.

Objective: To evaluate the effects of effective lens position (ELP) on the corneal plane effective cylinder power of toric intraocular lenses (IOLs).

Design: Retrospective cross-sectional study.

Participants: Ninety-four eyes from 78 patients who underwent uncomplicated phacoemulsification with implantation of an AcrySof toric IOL (1.50- to 3.00-D cylinder).

Methods: The amount of corneal plane effective cylinder power of toric IOLs given by the manufacturer (target-induced astigmatism vector [TIA]) was compared with the postoperatively achieved cylindrical correction (surgically induced astigmatism vector [SIA]). The theoretical corneal plane cylinder power of toric IOLs was calculated according to ELP and corneal power using a refractive vergence formula.

Results: The TIA (1.59 ± 0.43 D) was significantly smaller than the SIA (1.78 ± 0.65 D; p < 0.001). The difference between the magnitudes of SIA and TIA demonstrated a significant negative correlation with ELP (r = -0.219 and p = 0.034). The theoretical corneal plane cylinder power of toric IOLs demonstrated a decreasing trend as the ELP and corneal power increased. The range of changes in corneal plane effective cylinder power according to ELP and corneal power was greater in toric IOLs with high toricity.

Conclusions: The cylinder power of AcrySof toric IOLs should be adjusted according to ELP. For eyes with small ELP, the cylinder power should be reduced, and for eyes with large ELP, the cylinder power should be increased. The amount of reducing or increasing cylinder power of toric IOLs should be increased as the toricity increases.