Increasing IOL power prediction accuracy

Reviewed by Robert J. Cionni, MD

Salt Lake City-Intraoperative aberrometry with a microscope-mounted proprietary device (ORA with VerifEye, Alcon Laboratories) significantly improves refractive outcomes after cataract surgery, according to results of a multicenter trial. 

Speaking on behalf of his co-investigators, Robert J. Cionni, MD, medical director, The Eye Institute of Utah, Salt Lake City, reported on the study that included 162 eyes. Refractive outcome was evaluated at 21 to 35 days after implantation of a monofocal, presbyopia-correcting or toric IOL. Some patients also received astigmatic correction with manual or femtosecond laser-created incisions.

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In all patients, IOL power was calculated preoperatively using newer generation, optimized formulas, but final power selection was guided by intraoperative aberrometry. Mean absolute value of the prediction error (MAVPE) and median absolute error (MAE) were calculated for the implanted IOL and presuming use of an IOL chosen based on the preoperative power calculation.

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The results showed that MAVPE was significantly lower using intraoperative aberrometry to guide IOL power selection compared with preoperative power prediction (0.29 ± 0.26 D versus 0.35 ± 0.37 D; p = 0.04). MAE and MAE range using intraoperative aberrometry were also lower than with the preoperatively calculated IOL power (0.22 versus 0.27 D and 0.01-1.47 D versus 0.00-3.17 D).

In addition, the distribution of eyes with an absolute error within 0.50 D of target was significantly higher using intraoperative aberrometry to guide IOL power selection compared with use of the preoperative power calculation (85% versus 76%; p = 0.025).

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“Our goal as surgeons is to get the refractive outcome right the first time in order to avoid an unhappy patient who needs an enhancement,” Dr. Cionni said. “Preoperative calculations for IOL power selection are good, but in my mind, not good enough to meet the higher expectations of today’s patient population.”

Seeing an advantage

Seeing an advantage

The results of this study show that even when surgery is performed in the best of hands by expert surgeons using advanced IOL power formulae and state-of-the-art preoperative and intraoperative techniques, there is an advantage for using intraoperative aberrometry for achieving better refractive outcomes.

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Looking at the data on MAE distribution suggests that out of the 162 eyes included in this study, an additional 14 might be expected to require an enhancement postoperatively because of excessive residual spherical error if the IOL power was selected based on the preoperative calculation, according to Dr. Cionni.

The version of the intraoperative aberrometer used provides streaming aphakic and pseudophakic intraoperative refractive information.  

“Streaming data allows the surgeon to evaluate the quality and stability of the reading before capturing the reading for IOL power selection,” Dr. Cionni said.

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Patients were eligible for inclusion in the study if they were at least 22 years old and were undergoing routine refractive cataract extraction or lens exchange surgery not involving other procedures.

Exclusion criteria included irregular astigmatism or other corneal abnormality and inability to achieve keratometric stability or adequate fixation for image capture with intraoperative aberrometry. Outcomes evaluators were masked to use of intraoperative aberrometry, IOL type, and whether the patient had any cornea-based astigmatic correction.

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Robert J. Cionni, MD

E: rcionni@theeyeinstitute.com

This article was adapted from Dr. Cionni’s presentation at the 2016 meeting of the American Society of Cataract and Refractive Surgery. Dr. Cionni is a consultant and lecturer for Alcon Laboratories.