A New Method for Calculating Residual Astigmatism Produced by Toric Intraocular Lens Rotation

Aims: To report a new method for calculating residual astigmatism when exact and inexact cylinder power toric intraocular lenses (IOLs) are rotated. Methodology: Using Excel spreadsheets and sin 2 ∏ values, we expressed the cylinder powers of toric IOLs in percentage terms compared to corneal astigmatic powers and calculated values for various corneal astigmatisms and toric IOLs. From these values, we created charts of residual astigmatic powers and axes demonst rating the results of IOLs ranging from 50% to 150% and rotated 0 ∫to 30∫. Results:Comparing residual astigmatic powers,the rank orders for e ach IOL were as follows: 100%<90%<80% at 5∫ of rotation, 90%<100%<80% at 10∫ of rotation, and 90%<80%< 75% <100% at 15∫of rotation. Thus, lower cylinder power IOLs perform better than higherpower IOLs when rotated over 5∫ . Furthermore, the residual astigmatic powers of 125% IOLs were always higher than those of 100% IOLs ; however,the residual astigmatic powers of 75% IOLs became lower than those of 100%IOLs when rotation exceeded 15∫. Conclusion: Our method shows thatlower cylinder power IOLs are advantageous in environments where IOL rotation is likely and when inexact IOLs are utilized.