Improving the Prediction of Astigmatism After Toric IOL Implantation
Purpose
To compare the relative contribution of surgical induced astigmatism (SIA), axis misalignment and method of prediction to unexpected outcomes after toric IOL Implantation.
Methods
The refraction, keratometry and axis of the implanted lens were measured postoperatively in a series of 54 Patients who had cataract surgery performed with a toric intraocular lens. Using vector calculations the error in predicted residual astigmatism was compared in a serial fashion by eliminating errors in assumed SIA and axis alignment. The relative contribution of these factors was estimated using different toric calculators and methods of calculation.
Results
With the Alcon calculator the percentage of cases with a predicted error in residual astigmatism of 0.75 D or less improved by 10% when errors in both SIA and Axis alignment were eliminated. Using the Barrett toric calculator improved the percentage of cases within 0.75 D of predicted error in residual astigmatism by an additional 30 percent. Eliminating errors due to SIA and axis alignment, 70.4 percent of cases had an error in predicted residual astigmatism within 0.5 D with the Barrett calculator vs 50% using the Holladay calculator modified with the Baylor nomogram or direct measurements of the posterior cornea obtained with a Pentacam Scheimpflug camera.
Conclusion
Assumed values for SIA and errors in alignment of the toric IOL axis played a smaller role than the method of calculation in this series.