Authors: Qayim Kaba, Hannah Chiu, Eric Tam, Raj Maini, Sohel Somani

Purpose: To determine and compare the prediction error using IOL Master, Pentacam and OPD corneal topography measurements for astigmatism correction using a Toric intraocular lens. 

Study Design: Prospective cohort study 

Methods: Consecutive patients with requiring correction of corneal astigmatism and undergoing cataract extraction and toric intraocular lens implantation were recruited. Corneal astigmatism was measured preoperatively using IOL Master, OPD, and Pentacam. Residual astigmatism was determined using vector analysis, with comparison of centroid astigmatism error for each of the three topographic methods. Intraclass correlation coefficient was used to determine the similarity between predicted and actual corneal astigmatism. Predicted axis was compared to post-operative axis to determine the measurement method most accurate for axis. 

Results: A total of 41 eyes of 30 consecutive subjects with corneal astigmatism undergoing cataract extraction with toric intraocular lens implantation and no other ocular comorbidities were included in the study. Centroid errors of prediction error in IOL Master, Pentacam, and OPD were 0.39@96, 0.36@92, and 0.33@76, respectively, in with-the-rule (WTR) eyes at post-operative month 1 (POM1). They were 0.40@68, 0.33@62, and 0.38@55 for against-the-rule (ATR) eyes. For ATR eyes, Pentacam had the lowest centroid prediction error and the highest ICC (P<0.01) between the predicted and estimated astigmatism. A statistical test of the residual astigmatism (cylindrical power) between pentacam and OPD for WTR eyes showed no significance (P>0.05). There was no statistical significance (P>0.05) for actual and predicted axis comparison between IOL Master, Pentacam, and OPD. 

Conclusions: Pentacam topography resulted in the least corneal astigmatism prediction error, especially in patients with ATR astigmatism. IOL Master showed the highest centroid astigmatism error in both WTR and ATR eyes.