Accuracy of Newer IOL Power Formulas in the Short and Long Eyes Using Sum-of-Segments Biometry

My name is Dr. H. John Shammas. I am a cornea, cataract, and refractive surgeon in private practice in Los Angeles, and a Clinical Professor in the Department of Ophthalmology at the University of Southern California. We recently conducted an investigator-initiated trial to evaluate the accuracy of recently developed intraocular lens power formulas in the short and in the long eyes. Specially when using sum-of-segments biometry. The ARGOS® SS-OCT biometer is unique in how it collects sum-of-segments biometric measurements, determining the optical path lengths of the cornea, aqueous depth, lens and vitreous using their specific refractive indices. I was very enthusiastic about understanding the outcomes that might be achieved when using ARGOS® measurements in combination with newer IOL power formulas. With this objective in mind, our retrospective study began with data from 595 eyes scheduled for cataract surgery at a single center. From this data pool, we identified 78 short eyes with axial length less than 22.5 mm and 102 long eyes with axial length greater than 24.5 mm. The groups were comparable with respect to mean age. Over 80% of the patients in the short eyes group were female, while 46% in the long eyes group were female. Expected residual refractions were calculated using a range of relatively recently developed formulas that calculate the intraocular lens power based on different combinations of parameters and metrics. Results obtained with these formulas were compared to those with commonly used traditional intraocular lens power formulas. Starting with the 78 short eyes, mean absolute error was lowest, between 0.31 and 0.33 D, with the Barrett True Axial Length, Emmetropia Verifying Optical, K6, the Olsen, and the PEARL-DGS formulas. The percentage of eyes achieving a refraction within 0.50 D of predicted ranged from 71.8 to 80.8% with these formulas. All traditional formulas tested resulted in a mean absolute error greater than 0.36 D. In the 102 long eyes analyzed, all newer intraocular lens formulas resulted in a mean absolute error equal to or less than any of the traditional formulas, with the lowest values achieved with the Barrett True Axial Length, Emmetropia Verifying Ocular, Hoffer QST, Kane, and the PEARL-DGS formulas. These formulas resulted in a range of 78 to 82.4% of eyes with a refraction within 0.50 D of predicted. Precise biometric measurements and IOL power calculations are essential to ensuring good cataract surgery outcomes. The ARGOS® Swept Source -OCT biometer’s sum-of-segments approach helps address the challenge of measuring the axial length in the short and the long eyes by using the refractive index of each segment of the eye. We know from previous work that ARGOS® can improve axial length measurements and absolute IOL power prediction in short and long eyes.1 The present study builds on these findings by demonstrating that a high level of accuracy can be achieved with sum-of-segments biometry and a variety of newer IOL power formulas. This is really encouraging for surgeons, since we are always looking for ways to improve our predictive accuracy. © 2022 Alcon Inc. US-ARB-2200062