System measures aphakic eyes

July 1, 2010

Intraoperative wavefront aberrometry using a proprietary system demonstrates the ability to measure refractive error accurately in aphakic eyes and represents technology that may improve accuracy of IOL power outcomes after cataract surgery.

"There are a variety of methods for calculating IOL power, but most depend on assumed corneal power from preoperative keratometry measurements and axial length that can be affected by cataract density," said Dr. Holland, director of cornea, Cincinnati Eye Institute, and professor of ophthalmology, University of Cincinnati, Cincinnati, OH.

"This intraoperative wavefront system enables real-time, on-the-table refractive assessment using the aphakic refractive function for both the corneal power and length of the eye so that it can potentially reduce . . . errors from keratometric readings and axial length obtained when the crystalline lens is still in the eye," he added.

Overall, with use of the intraoperative wavefront aberrometer, 75% of eyes were within 0.50 D of targeted power and 98% were ±1.0 D. The mean predictive error was 0.38 D.

"These results compare favorably [with] recently published data on IOL power accuracy using traditional preoperative techniques," Dr. Holland said. "In a study of about 4,800 eyes, Gale et al. reported that 55% of eyes were within 0.5 D of target and 85% were within 1 D. Narváez and Stulting studied 643 eyes and reported a mean predictive error of 0.52 ± 0.44 D."

Consistent benefits

The data also were analyzed for the three most commonly used IOLs in the series, and the results showed consistent benefits associated with use of the intraoperative data.

For 35 eyes with the MI60L IOL (Akreos AO Microincision, Bausch + Lomb) implanted, the mean predictive error was 0.38 D using the preoperative measurements, but only 0.2 D using the intraoperative data. The rate of accuracy to target within 0.5 D improved from 69% based on the preoperative calculations to 86% using the data obtained in the aphakic eye, while all refractive outcomes were within 1 D of target using either method.

There were 26 eyes with the SN60WF IOL (AcrySof IQ, Alcon Laboratories) implanted. Mean standard error was 0.33 D using the preoperative data and 0.1 D with the intraoperative data. Accuracy to target within 0.5 D improved from 85% to 100% with use of the aphakic data while accuracy to target within 1 D was 96% using the preoperative data and 100% using the intraoperative measurements.

For 32 eyes with the ZCB00 IOL (Tecnis 1-piece, Abbott Medical Optics) implanted, mean predictive error was 0.55 D using the preoperative data and only 0.26 D using the intraoperative data. The intraoperative method markedly increased the rate of accuracy to target within 0.5 D from 47% to 84%, while accuracy to target within 1.0 D was 87% using the preoperative data and 100% using the intraoperative aphakic wavefront refraction.

FYI

Edward J. Holland, MD
E-mail: eholland1@fuse.net

Dr. Holland is a consultant to WaveTec Vision.