Comparing surgically induced astigmatism calculated by means of simulated keratometry versus total corneal refractive power

Abstract

Purpose:

To evaluate surgically induced astigmatism as computed by means of either simulated keratometry (K_SIM) or total corneal refractive power (TCRP) after temporal incisions.

Methods:

Prospective observational study including 36 right eyes undergoing cataract surgery. Astigmatism was measured preoperatively during the 3-month follow-up period using Pentacam. Surgically induced astigmatism was computed considering anterior corneal surface astigmatism at 3 mm with K_SIM and considering both corneal surfaces with TCRP from 1 to 8 mm (TCRP₃ for 3 mm). The eyes under study were divided into two balanced groups: LOW with K_SIM astigmatism <0.90 D and HIGH with K_SIM astigmatism ≥0.90 D. Resulting surgically induced astigmatism values were compared across groups and measuring techniques by means of flattening, steepening, and torque analysis.

Results:

Mean surgically induced astigmatism was higher in the HIGH group (0.31 D @ 102°) than in the LOW group (0.04 D @ 16°). The temporal incision resulted in a steepening in the HIGH group of 0.15 D @ 90°, as estimated with K_SIM, versus 0.28 D @ 90° with TCRP₃, but no significant differences were found for the steepening in the LOW group or for the torque in either group. Differences between K_SIM- and TCRP₃-based surgically induced astigmatism values were negligible in LOW group.

Conclusion:

Surgically induced astigmatism was considerably higher in the high-astigmatism group and its value was underestimated with the K_SIM approach. Eyes having low astigmatism should not be included for computing the surgically induced astigmatism because steepening would be underestimated.

Keywords

Astigmatism cataract surgery posterior cornea multifocal intraocular lens surgically induced astigmatism

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