Role of aberrometry may reduce refractive ‘surprises’

February 15, 2015

Intraoperative aberrometry may reduce refractive surprises and result in a higher percentage of happy patients following cataract surgery, particularly those who had undergone previous corneal refractive surgery and in those planning for a toric IOL.

 

Take home message: Intraoperative aberrometry may reduce refractive surprises and result in a higher percentage of happy patients following cataract surgery, particularly those who had undergone previous corneal refractive surgery and in those planning for a toric IOL.

 

By Michelle Dalton, ELS; Reviewed by Robert Cionni, MD

Salt Lake City-As more and more patients are expecting refractive outcomes with their cataract surgery, the use of intraoperative aberrometry may reduce refractive "surprises" and result in a higher percentage of happy patients. Surgeons are finding the technology particularly helpful with eyes that had undergone previous corneal refractive surgery and in those under consideration for a toric IOL.

More in this issue: Keys to IOL power selection in pseudophakic children

One system (ORA System with VerifEye, WaveTec Vision/Alcon Laboratories) has been invaluable, said Robert Cionni, MD, medical director of The Eye Institute of Utah, Salt Lake City. The technology has the ability to take into account the effect of posterior corneal astigmatism and to consider the aphakic refractive state for patients who have previously undergone corneal refractive surgery, he noted.

“The improvement VerifEye gives us with toric IOLs is also seen with corneal astigmatic incisions and with spherical refractive errors,” he said. “I alter my planned IOL spherical power in approximately 50% of eyes based on the information that VerifEye provides me during surgery. Nailing the refractive result is of particular importance when using multifocal IOLs or toric IOLs.”

According to manufacturer data, in a study of more than 1,300 eyes, the mean preoperative keratometric astigmatism (1.72 D) dropped to a mean of 0.42 D postoperatively when the system is used with toric IOL implantation.

 

Next: How the system works

 

The latest hardware upgrade (the VerifEye+) provides real-time, streaming refractive information on the preview screen, as well as a dynamic reticle that tracks the patient’s pupil during surgery.

Once the cataract has been removed, the eye is pressurized to about 21 mm Hg. The patient looks at the fixation light and in about 4 seconds, 40 wavefront readings are taken which results in an aphakic refraction being obtained, Dr. Cionni explained.

Proprietary software “then calculates a recommended IOL power and the refractive result, as well as the amount of astigmatism and its axis," he said. "If a toric IOL is planned, the software also recommends a toric magnitude and its alignment."

If implanting a toric IOL, a dynamic reticle tracks the pupil and guides the surgeon to the correct alignment for the IOL. Once aligned, a pseudophakic measurement confirms the reduction in cylinder, Dr. Cionni noted.

 

Minimizing errors

Before using intraoperative aberrometry, surgeons would typically base toric IOL choices on anterior corneal curvature as measured by keratometry coupled with the manufacturer’s toric IOL calculator, disregarding corneal pachymetry, anterior chamber depth, and estimated lens position. However, studies have shown calculating cylindrical compensation without considering those other aspects may not give surgeons accurate results.1,2

 

A masked, prospective, contralateral randomized study of 111 patients compared the ORA System with VerifEye with the Alcon online toric calculator. In patients scheduled for toric IOL implantation, the percentage of patients with less than 0.5 D residual astigmatism was 89% in the VerifEye eyes and 77% in the toric calculator eyes, Dr. Cionni said.

That equates to an almost 13% increase in the percent of patients within 0.5 D of intended target at the 1 month follow-up, he said.

“My personal experience is even better with about 95% of eyes showing less than 0.5 D residual refractive cylinder when utilizing VerifEye,” he said. He originally compared calculations provided by the ORA system against his manual calculations and found the ORA was “typically within 0.5 D of manual readings for spherical power,” but the device was more accurate for the power and alignment of toric IOLs.

Residual astigmatism is usually attributable to posterior corneal astigmatism, according to recent studies.3

“Doug Koch, MD’s recent work showed us that the curvature of the posterior cornea has a significant effect on refractive astigmatism in many eyes and therefore, should not be ignored,” Dr. Cionni said. “The ORA takes the effect of the posterior cornea into account.”

Measuring just the anterior cornea will not predict astigmatic correction; surgeons need to consider both anterior and posterior corneas. Dr. Koch’s group also found against-the-rule (ATR) and with-the-rule (WTR) posterior astigmatism are responsible for postoperative over- and undercorrections, respectively.

The ORA is able to correct both ATR and WTR astigmatism with equal aplomb, Dr. Cionni said.

“However, regular ‘bow-tie’ astigmatism reduction is more predictable than irregular astigmatism,” Dr. Cionni said.

 

Because of its accuracy, Dr. Cionni “regularly” uses the system with his premium IOL patients.

The streaming refractive information and “enhanced astigmatic feedback” from the VerifEye+ is likely to improve his postoperative results even more, Dr. Cionni said.

With the demands of today’s premium IOL patients, devices and technologies that allow surgeons to hit refractive targets more often are not only desirable, but necessary.

 

References

1.     Goggin M, Moore S, Esterman A. Outcome of toric intraocular lens implantation after adjusting for anterior chamber depth and intraocular lens sphere equivalent power effects. Arch Ophthalmol. 2011;129:998-1003.

2.     Goggin M, Moore S, Esterman A. Toric intraocular lens outcome using the manufacturer's prediction of corneal plane equivalent intraocular lens cylinder power. Arch Ophthalmol. 2011;129:1004-1008.

3.     Koch DD, Ali SF, Weikert MP, et al. Contribution of posterior corneal astigmatism to total corneal astigmatism. J Cataract Refract Surg. 2012;38:2080-2087.

 

 

Robert Cionni, MD

E: rcionni@theeyeinstitute.com

Dr. Cionni is a consultant to WaveTec Vision and Alcon Laboratories.