The accuracy of IOL power calculations continues to improve with the use of modern instruments for biometry, updated formulas, and constant optimization. However, unusual eyes still present a challenge, and residual refractive error still occurs in a clinically significant proportion of normal cases, said Giacomo Savini, MD.
There are differences, however, in the performance of available formulas, and results from various published studies show that better outcomes are achieved by using the newer formulas that take anterior chamber depth into account for the estimation of the IOL position, Dr. Savini said. Some formulas introduced more recently include the Barrett Universal II, EVO, Hill-RBF, Kane, Naeser, Olsen, Panacea, and Pearl-DGS, and most of those can be accessed for free online.
A recent study by Dr. Savini and colleagues compared the accuracy of 15 IOL power calculation formulas, including many of the newer formulas [Savini G, et al. J Cataract Refract Surg. In press https://www.jcrsjournal.org/article/S0886-3350(19)30641-8/fulltext]. Using data from 150 eyes that were all measured with the same biometer, received the same model IOL, and operated on by one of two surgeons, the analyses showed that the prediction error was within 0.5 D in almost 90% of eyes.
“With seven of the formulas, a prediction error ≤0.5 D was achieved in ≥88% of eyes. Even the older formulas did not do so bad because with their use, about 85% of eyes were within 0.5 D of the intended target, which is still a good result,” Dr. Savini said.
Particularly interesting, however, was the finding that a prediction error ≤ 0.25 D was achieved in the majority of cases (51% to 62%), regardless of the formula used. The best results were achieved with the Kane and Barrett formulas, both of which had a prediction error ≤0.25 D in 62% of eyes.
“As the next frontier, I think we will be classifying performance of IOL calculation formulas by the percentage of eyes with a prediction error lower than 0.25 D instead of 0.50 D,” Dr. Savini said.
Giacomo Savini, MD
E: [email protected]
This article is based on a paper presented by Dr. Savini at the 37th Congress of the European Society of Cataract and Refractive Surgeons. Dr. Savini is a consultant to, a speaker for, and/or receives research support from companies that manufacture IOLs and instruments for biometry.