Abstract
Purpose :
Patient’s with significant corneal astigmatism may benefit from placement of a toric intraocular lens (IOL). To ensure optimal vision post operatively, accurate keratometry values must be taken. New algorithms provide options to include posterior corneal astigmatism (PCA) into calculations at the user discretion. Accounting for PCA significantly changes the predicted residual astigmatism over a range of intraocular lens (IOL) powers but at varying magnitude depending on the base data.
Methods :
Using the TECNIS® IOL Calculator, we calculated residual astigmatism with and without inclusion of PCA, while manipulating keratometry values. Steep K2 values were fixed at 40D, 45D, and 50D. Flat K1 values were manipulated 35D, 40D, and 45D respectively, and increased in increments of 0.5D. Clinically relevant IOL powers were used from 15D to 34D in increments of 0.5D. The lowest residual astigmatism was used for each data point. The main outcome calculated was residual astigmatism with and without PCA. Mean absolute error (MAE) and a two tailed t-test with a p-value ≤ 0.05 were used to calculate statistical significance.
Results :
For steep K2 value fixed at 40D, K1 values at 35D, 35.5D, 36D, and 36.5D were used with and without PCA selection. MAE of residual astigmatism at 35D was 0.44 (p<1.4 x 10-64), 35.5D was 0.15 (p<1.16 x 10-12), 36D was 0.07 (p<0.28), and 36.5D was 0.08 (p<4.8 x 10-6). For steep K2 value fixed at 45D, K1 values at 40D, 40.5D, 41D, and 41.5D were used with and without PCA selection. MAE of residual astigmatism at 40D 0.56 (p<1.7 x 10-69), 40.5D was 0.25 (p<3.2 x 10-30), 41D was 0.09 (p<0.04), and at 41.5D was 0.09 (p<1.6 x 10-7). For steep K2 value fixed at 50D, K1 values at 45D, 45.5D, 46D, and 46.5D was used. MAE of residual astigmatism at 45D was 0.67 (p<7.5 x 10-64), 45.5D was 0.39 (p<8.3 x 10-48), 46D was 0.12 (p<0.005), and at 46.5D was 0.07 (p<0.13).
Conclusions :
Over a range of keratometry values, there was statistically significant difference in calculated residual stigmatism when accounting for PCA when a manufacturer’s calculator is used, and should be accounted for when calculating patient’s IOL. However, at flat K1 values of 36D and 36.5D at a fixed steep K2 value of 40D, and flat K1 values of 46.5D at a steep K2 value of 50D were not statistically significant. This is primarily due to manufacturing limits.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.