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Fatma Dihowm, David Hjelmstad, Samir I Sayegh; Comparison of Astigmatism Calculation Methods for FDA approved Toric Intraocular Lenses. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3749.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To compare the results of FDA Toric IOL Calculators, and assess their accuracy in predicting IOL power in patients with astigmatism.
Methods: In this comparative study, the three software programs for calculation of Toric IOL were identified and used to calculate Toric IOL of 90 standardized cases, 30 in each calculator. IOL spherical equivalent (SE) of 10, 15, 20, 25, and 30 were used to calculate the toric IOL power. Flat keratometer reading (K1) was chosen to be 42 D at axis 0 and steep keratometer reading (K2) were 43, 44, 45, 46, 47, or 48 D at axis 90. Surgically Induced Astigmatism (SIA) was taken as zero and Incision Location (IL) at 90. The calculation was done to each SE and repeated by changing K2 reading each time. The amount of predicted residual astigmatism was compared. A direct comparison was possible for two out of three manufacturers as they provide identical toric corrections for a subset of their lenses.
Results: The amount of residual astigmatism predicted differed significantly between manufacturers, but at low level of astigmatic correction, was not at the level of clinical significance.
Conclusion: The study demonstrates significant differences in the methodology and results of toric IOL calculation between manufacturers. These differences may be clinically significant at higher levels of attempted astigmatic correction. The introduction of a universal toric intraocular lens calculator rooted in an exact astigmatic calculation and taking into consideration all relevant anatomical variables is warranted.
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