Wavefront aberrometry can improve toric IOL outcomes

Take-home

Using technology in place of conventional corneal measurements and nomograms for selection and placement of toric IOLs can improve patient outcomes.

Dr. CionniBy Fred Gebhart; Reviewed by Robert J. Cionni, MD

Salt Lake City-Clinicians can improve postoperative outcomes for patients with astigmatism who receive toric IOLs by adding a wavefront aberrometer to the standard operative workflow.

“We clearly get better results using an intraoperative wavefront aberrometer-more accurate results-compared [with] conventional techniques for toric IOL selection and placement,” said Robert J. Cionni, MD, medical director, The Eye Institute of Utah and adjunct clinical professor, at The University of Utah Moran Eye Center, Salt Lake City.

“Indeed, I will no longer implant a toric IOL without guidance from an aberrometer,” he said. “Up until the introduction of aberrometry, we typically have utilized calculations and nomograms that point us to the best result for the average of a group of patients. Now by utilizing aberrometry, we can determine the best answer for each individual patient.”

Outcomes could be improved

Results of a recent study do not yet change the standard of care for toric IOL implants, Dr. Cionni noted. However, the data offer clear evidence that outcomes achieved using convention techniques can be significantly improved.

The study looked at 65 eyes that had at least 1.5 D of preoperative keratometric astigmatism. All of the patients were scheduled for cataract surgery with the implantation of a toric IOL. The initial cylinder power was selected based on standard measurements of anterior corneal curvature and a standard toric IOL nomogram. The steep axis was marked prior to surgery in keeping with standard procedures.

After phaco, the aphakic refraction was measured (ORA System, WaveTec Vision). The aberrometer was used to verify the magnitude and axis of refractive astigmatism and to determine the optimal cylinder power and axis for the lens to be implanted.

After the final lens selection, ORA was used for pseudophakic measurements and the IOL was rotated to the optimal axis using ORA’s retile as a guide for final placement. A final measurement was taken to confirm correct positioning.

For most patients, 36 eyes (55%), ORA cylinder recommendations recommended a cylinder power other than the power calculated using standard methods. ORA recommended a decrease in power for 27 eyes and an increase for 9 eyes.

“Usually these changes were just one magnitude power difference, representing 0.75 D,” Dr. Cionni said. “But in five cases there was a decrease of 2.25 D and another case with an increase of 2.25 D. If the aberrometer was right, these recommendations would mean the difference in having to do a second procedure because we had used the wrong implant the first time.”

The difference, he explained, is that standard methodology is based on anterior corneal curvature. Posterior curvature is poorly understood and not typically measured, nor are other potential sources of aberration.

Comparing preoperative keratometric astigmatism with aphakic refractive astigmatism measured using ORA confirmed recent results presented by Doug Koch, MD suggesting that traditional methods tend to underestimate against-the-rule astigmatism and overestimate with-the-rule astigmatism, Dr. Cionni continued.

Wavefront aberrometry is able to take into account posterior corneal curvature, which appears to average about 0.5 D different from anterior corneal curvature measurements.

Pre- and postoperative measurements confirm that aberrometry can improve outcomes. The mean preoperative astigmatism was 2.01 D ± 1.04 D. The mean postoperative refractive astigmatism was 0.33 D ± 0.35 D.

Though this was not a head-to-head comparison of conventional technique versus wavefront aberrometry, historical data on 244 eyes provides a useful comparison. The mean ORA postoperative refractive astigmatism of 0.33 D compared with a postoperative mean of 0.55 D in historical controls. The average cylinder reduction for ORA patients was 84% compared with 62.4% reduction for historical data.

Just over half of ORA eyes (54%) had postoperative refractive astigmatism of 0.25 D or less. More than three-quarters of ORA eyes (78%) had 0.5 D or less postoperative refractive astigmatism compared with 62% of historical eyes. Nearly all ORA eyes (98%) had one D or less of postoperative refractive astigmatism compared with 88% of historical eyes.

Most ophthalmologists who implant toric IOLs do not utilize a wavefront aberrometer, said Dr. Cionni, noting that the standard of care for astigmatism will not and cannot change until more practitioners have access to the technology.

“I truly believe that I would be doing my patients a disservice if I didn’t use an aberrometer when placing a toric implant,” Dr. Cionni said. “The bottom line is that when we looked at results using aberrometry-guided placement of toric implants compared [with] the historical method, the aberrometer was significantly better.”

Robert J. Cionni, MD

E: rcionni@theeyeinstitute.com

Dr. Cionni is a paid consultant for WaveTec Vision.

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