Comparison of two strategies estimating surgically induced astigmatism in position prediction of toric IOLs in 2.2 mm cataract surgery.

PURPOSE

To compare the precision of the arithmetic mean of surgically induced astigmatism (M-SIA) and the centroid of surgically induced astigmatism (C-SIA) in estimating SIA when predicting the power and axis of toric IOLs under different circumstances.

METHODS

120 eyes of 99 patients undergoing toric IOL replacement in a simple cataract surgery were included in the retrospective study. The predicted position of toric IOL was calculated by Z Calc online calculator and Barrett Toric Calculator with M-SIA (0.4D) or C-SIA (0.1D). Position prediction error (PPE, the difference between the predicted position of toric IOL and the ideal position of toric IOL), its absolute value (PPE-Abs) and △PPE (the difference between absolute value of PPE calculated by C-SIA and by M-SIA using the same toric calculator) were used to evaluate the precision in estimate of SIA.

RESULTS

Statistical significance in mean PPE and mean PPE-Abs was found in the group M-Barrett. The orientation of corneal astigmatism and eye laterality were influential to mean PPE while gender was not. △PPE was below 0 in both toric calculators. Significant difference in △PPE was seen between groups with different corneal astigmatism when all eyes were OS, as well as between groups with different eye laterality when all eyes were with WTR astigmatism.

CONCLUSIONS

We did not find a significant difference between M-SIA and C-SIA in estimating the SIA of the patients undergoing small-incision cataract surgery combined with toric IOL implantation. M-SIA was not recommended in Barrett Toric Calculator. The orientation of corneal astigmatism and the incision on the cornea should be considered when choosing between M-SIA and C-SIA.

KEY MESSAGES

WHAT IS KNOWN? : Either the arithmetic mean of surgically induced astigmatism (M-SIA) or the centroid of surgically induced astigmatism (C-SIA) of a cohort was used to estimate the position of toric IOLs before the surgery. The size and site of corneal incision could influence the orientation and the magnitude of SIA. WHAT IS NEW? : When calculating the axis of toric IOLs with Barrett Toric Calculator, arithmetic mean of SIA (M-SIA) was not recommended for estimate. The orientation of corneal astigmatism could influence the estimate of SIA. We created several novel variables that could be used to indirectly evaluate the stability of toric IOLs and the prognosis of patients.