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Samir I Sayegh; Toric IOL Calculations for Refractive Cataract Surgery: The Good, The Bad, and The Distorted. Invest. Ophthalmol. Vis. Sci. 2016;57(12):925.
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© ARVO (1962-2015); The Authors (2016-present)
With the rising success of toric intraocular (tIOL) lenses to correct astigmatism at the time of cataract surgery, the repertoire and range of such lenses have been rapidly expanding and associated calculators, specific to a manufacturer or more broadly defined, have proliferated. The purpose of this presentation is to examine the underlying algorithms and methods used, properly or improperly, by a variety of calculators. Good methodologies emerge but also some serious limitations and these are classified as good, bad or distorted.
The consideration of tIOL calculators were evaluated on the following criteria1) Stand-alone-toric or allowing for sphere computation2) Sequential computation of sphere then toric components or allowing for simultaneous optimization3) Appropriate addition/combination of corneal astigmatism and surgically induced astigmatism4) Allowing for additional astigmatism combination such as that created by second incision or limbal relaxing incision (LRI)5) Use of fixed toricity ratio, variable toricity ratio or combination6) Allowing for meridional methods and its propoer implementation7) Appropriate interface with flexibility for re-computation and comparison8) Ease of use of the graphical user interface (GUI)
From the methods of computations examined, the majority of calculation environments were found to be stand-alone-toric implementing one portion of a necessarily sequential algorithm. The methods of combining astigmatism were generally appropriate but lacking generality, placing the burden of additional computations on the user. Some did not display cross cylinder necessitating indirect methods to elucidate results. Fixed toricity ratio methods were still broadly used despite a growing awareness of their inappropriateness. The meridional methods can be inappropriately applied, resulting in distorted results. Flexibility for re-computation and comparison was limited with few exceptions. There was a significant variability in user experience and quality/functionality of GUI, including the generation of a specific clear easy to use surgical plan.
While the use of tIOLs is growing rapidly with an increasing range and repertoire of options for the patients, calculation environments have continued to lag. A diagnostic approach and systematic classification of significant flaws is proposed along with suggested methods to address the shortcomings.
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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