Evaluation of Different Corneal Powers Measured by Corneal Tomography in Intraocular Lens Power Calculation

Abstract

Abstract Background Corneal power measurement is essential for IOL power calculation. Conventional keratometry measures the anterior corneal surface using a standard keratometric index without measuring the posterior corneal surface. Schiempflug imaging have added the ability to measure posterior corneal surface which may affect IOL power calculation and postoperative refraction. Purpose To evaluate different keratometric measurements including Simulated keratometry (SimK), true net power (TNP), total corneal refractive power (TCRP) and equivalent K reading (EKR) obtained from corneal tomography in IOL power calculation and compare the predicted refraction of calculated IOL power with postoperative subjective refraction. Materials and Methods Sixty-five cataractous eyes were included in this prospective interventional case series. Four corneal power measurements using Pentacam AXL were analyzed: SimK over 3mm, TNP over 4mm, TCRP over 3mm and EKR over 4.5mm. The IOL power was calculated using Barrett Universal II formula. Results No statistically significant difference between SimK and EKR (p- value=1.000) while TNP and TCRP were statistically significantly higher than SimK (p-value<0.001) with mean difference 1.2+/-0.2D and 0.67+/-0.34D respectively. The mean prediction error of refractive outcome was -0.006+/-0.32D for SimK, -0.02+/- 0.5D for EKR, 1.08+/-0.4D for TNP and 0.56+/-0.46D for TCRP. Conclusion Corneal power measurements using SimK and EKR displayed comparable accuracy in IOL power calculation and postoperative refraction while TNP and TCRP were far away.