Refractive Outcomes Using Simulated Keratometry Versus Keratometry From an Optical Biometer

Abstract

Purpose

To compare refractive prediction accuracy using simulated keratometry (SimK) measurements obtained from a Scheimpflug tomographer (Pentacam AXL, Oculus) versus keratometry (K) measurements obtained from an optical biometer utilizing telecentric keratometry (IOLMaster 700 (IOLM700), Carl Zeiss Meditec AG) applied to modern IOL power calculation formulas.

Design

Retrospective accuracy and validity analysis

Methods and Setting

Private practice center

Study Population

Five hundred eighty-nine eyes with preoperative SimK and K measurements undergoing phacoemulsification and implantation of monofocal IOL (Clareon SY60WF IOL, Alcon Laboratories, Inc.). Using IOLCon constants and optimized lens constants, nine IOL formulas (Barrett Universal 2.0 (BU2), Cooke K6 (K6), EVO 2.0, Haigis, Hoffer Q, Holladay I, Pearl DGS, SRK/T, and T2) were used to calculate refractive prediction errors across 3 methods: (1) IOLM700 biometry (axial length (AL), anterior chamber depth (ACD), and K), (2) Pentacam AXL biometry (AL, ACD, and Sim K), and (3) combined IOLM700 AL/ACD with Pentacam AXL Sim K

Main Outcome Measures

Mean absolute error (MAE) and root mean squared error (RMSE) were used to assess refractive outcomes.

Results

Using both nonoptimized (IOLCon) and optimized lens constants, all nine formulas demonstrated the lowest MAE and RMSE with the IOLMaster 700 approach, followed by the combination approach, and then the Pentacam AXL approach. Formula rankings varied among the 3 techniques: the K6 formula had the highest ranking for the IOLM700 technique, while EVO 2.0 had the top ranking for the Pentacam and combination techniques. When applying heteroscedastic testing to compare the 3 methods within each of the nine formulas, the IOLM700 version was significantly better than the combination version (all P < .05), and the combination version was superior to the PC version (all P < .05). Among the top-performing Pentacam formulas, the BU2 and Haigis formulas were statistically similar to the EVO 2.0

Conclusions

Biometric values (including standard K) from the IOLM700 provided the most accurate refractive predictions across formulas, outperforming biometric values (including Sim K) from the Pentacam AXL, even after lens constant optimization. Sim K values are not directly interchangeable with SS-OCT biometer-derived K values. The performance of formulas varies based on the source of biometry and optimization.