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Zhangying Chen, Samir I Sayegh; Cross Cylinder Calculation Agreement Amongst toric IOL Calculators and UniversIOL. Invest. Ophthalmol. Vis. Sci. 2016;57(12):927.
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© ARVO (1962-2015); The Authors (2016-present)
As toric intraocular lenses (tIOLs) for the simultaneous correction of astigmatism and refractive error in patients undergoing cataract surgery become more sophisticated and more widespread, it is crucial to determine the appropriate amount of astigmatism to be corrected for the implantation of such lenses. The initial step of any such algorithm is the addition of the preexisting corneal astigmatism to the astigmatism induced by the incision(s) of the surgery, or surgical induced astigmatism (SIA). Such a step, the analytical aspects of which dates back to the 19th century, is made by all toric calculators and made explicit by most, but not all. We propose to verify that the results of such a calculation as performed by different toric calculators for major manufacturers, as well as by a universal calculator, are identical.
We compare the results of such calculations for seven different calculators. Three calculators for tIOLs that are FDA approved and three calculators for tIOLs available internationally but not in the US. We finally compare results to a universal calculator, UniversIOL, that provides power calculation for all intraocular lenses, including toric lenses.A standardized power set of 6 values of corneal astigmatism each at 6 different angles, combined with 6 values of SIA, also at 6 different angles were combined to yield the "crossed astigmatism" for each one of 6 commercially available calculators (5 online and one in an app). The results were tabulated then compared to results obtained by UniversIOL.
All 6 calculators yielded nearly identical results for the cross cylinder and agreed with results from UniversIOL. The only difference was that for some cases one calculator differed by one degree and that UniversIOL provided one additional significant digit which may or may not be useful surgically.
There is general agreement in the results for cross cylinder amongst multiple calculators (and UniversIOL provides higher precision). This is important since all computations of an appropriate tIOL involve this crucial step. The reason for the discrepancies observed in residual astigmatism for the same eye implanted with equivalent tIOL from different manufacturers (F Dihowm and S Sayegh, ARVO 2014, AAO 2014) must originate at a different step of the computation (Gabra and Sayegh, ARVO 2014).
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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