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M. Bird, S. Norrby, L. Wang, D. Koch, P. Piers; Calculating IOL Power for Myopic LASIK Patients Using Real Ray Tracing. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5603.
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© ARVO (1962-2015); The Authors (2016-present)
It is sought to find a reliable method to calculate the IOL power needed for cataract patients who have previously undergone myopic LASIK surgery. The current study examines 35 highly aberrated myopic LASIK patient eyes and reports on four metrics for the evaluation of IOL power calculation: one that minimizes defocus, two that maximize the radial MTF, one at 6 c/deg and another at 30 c/deg and one that maximizes the area under the radial MTF curve. It is also the purpose of this study to compare these results to current IOL power calculation methods in order to determine whether or not the same formulas can be applied to post-LASIK eyes.
Clinical measurements of ACD, AL and K along with corneal topographies of 35 real LASIK eyes were integrated into Zemax to create individual eye models. A corneal thickness of 0.5mm was assumed and the curvature of the posterior surface was determined using the Dubbelman ratio. Three IOL designs were added to the models: a lens with positive spherical aberration, a lens that has zero spherical aberration, and a lens designed to correct the average pseudophakic corneal spherical aberration. For each design the lens was exchanged to satisfy, individually, the four metrics. A comparison across metrics was made using a Student’s t-test as well as an F-test with a significance level of P = 0.05. The results were also compared to an average IOL power as well as to the Adjusted Atlas0-3 (AA03) IOL power calculations.
The simulations provided average SE refractions of 0.14 D for the first two IOL types and -0.13 D for the third. It was found comparing across metrics that all metrics used were not significantly different from one another. It was also shown that the results from the metrics were not significantly different from the Adjusted Atlas0-3 power calculations but were however significantly different from the average of 5 IOL power calculators.
Real ray tracing (RRT) is a valuable tool for calculating the proper IOL power needed for LASIK patients. On average the ray tracing results for IOL power agree with the power calculated by the AA03 calculator, and on a patient-by-patient basis RRT ensures a minimum SE refraction.
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