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Physician: Refractive cataract surgery should have outcomes as accurate as LASIK
A combination of intraoperative aberrometry with streaming refractive data and femtosecond laser enhances the precision of cataract surgery outcomes.
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In contemporary refractive cataract surgery, I believe our goal should be to achieve results that are similar to outcomes in corneal refractive surgery. To me, that means that more than 90% of eyes should be within 0.5 D of plano, for both sphere and cylinder. We know that patients with premium IOLs have high expectations and a low tolerance for residual error. I find that within that ±0.5 D “sweet spot” we can meet those expectations, maintaining high patient satisfaction and a low enhancement rate.
However, in a recent analysis of more than 17,000 procedures, emmetropia, measured as spherical equivalent of ±0.5 Dand less than 1 D astigmatism, was reached in only 55% of eyes planned for emmetropia. Warren Hill, MD, estimated that, even with the best IOL power calculation methods and with optimized lens coefficients, only about 70% of eyes will be within ±0.5 D after cataract surgery. That falls far short of the 93% of eyes that achieve emmetropia after LASIK.
Technology aids precision
In our practice, femtosecond laser technology and intraoperative aberrometry — two relatively recent additions — have greatly improved the precision of cataract surgery, bringing our results close to those of LASIK.
The femtosecond laser we use for cataract surgery (LenSx, Alcon) improves precision in several areas, including the size and regularity of the capsulotomy. Without the femtosecond laser, there are variations in capsulorrhexis creation that affect the refractive outcome, even in anatomically similar eyes implanted with the same power IOL. By ensuring that I get a 5-mm capsulotomy in every case, I can “even out” variations that occur due to the lens sitting more posteriorly or anteriorly in an eye with a slightly smaller or larger capsulotomy.
Additionally, we use the Optiwave Refractive Analysis (ORA) System (Wave-Tec Vision) in all cataract cases with a refractive outcome goal, including cases with a toric or multifocal IOL, femtosecond laser arcuate incisions or monovision and post-refractive cases in which continued spectacle independence is desired. I generally do not perform these cases without ORA because I know that my odds of getting the right answer are vastly improved.
Intraoperative aberrometry technology has evolved considerably from the first-generation ORange to ORA and now ORA with VerifEye. VerifEye doubles the device’s image processing speed and provides the surgeon with continuously streaming refractive data up to and during measurement. This makes it easy to see when the eye is in a stable, ready state for the aberrometry reading and if anything happens to change that state. For example, if a side-port incision is leaking, the IOP can decrease, causing variations in the refraction. This is immediately visible with VerifEye, while it would have been nearly impossible to notice without it. For me, the biggest advantage of the streaming data is that it increases my confidence in the ORA refraction and lens power recommendation.
Study results
In a multicenter study of 202 eyes designed to test how the intraoperative aberrometer performs with streaming refractive data, the percentage of eyes with a spherical equivalent of ±0.5 D at 1 month improved from 80% with ORA to 84% using ORA with VerifEye (Figure 1). Both compare well to the 55% to 70% estimates cited earlier.
A gain of 4 percentage points with the upgrade to streaming refractive data may sound like little, but it matters. If we assume an increased likelihood of enhancement for eyes outside of that ±0.5 D range, that could mean four more enhancements out of every 100 cases — or for me, four more enhancements every month.
The data from my own center further demonstrate the power of incremental improvements. In our case, the percentage of eyes within ±0.5 D increased from 84% with ORA to 88% with ORA and the LenSx femtosecond laser and, finally, to 92% using ORA with VerifEye and the femtosecond laser (Figure 2). Each small increase in precision gets us closer to consistently achieving the desired refractive endpoint.
Toric IOL accuracy
Toric IOL implantation presents special challenges to the surgeon concerned with refractive accuracy. In addition to all the variables involved in achieving a plano spherical correct, we also have to choose the correct cylinder power and align the IOL on the correct axis. The reference and alignment marks present opportunities for error, as does the potential for posterior corneal astigmatism contributing to the refractive result. Douglas Koch, MD, has shown that posterior corneal curvature contributes, on average, about 0.5 D more against-the-rule astigmatism than is measured on the anterior cornea. However, one cannot just factor this into the planned astigmatism correction. Some eyes will have no posterior corneal astigmatism at all; others will have 1.5 D; and still others will have 1.5 D, 90° away from where one expects it to be. Without intraoperative aberrometry, we currently have no practical way of identifying or figuring out how to correct posterior corneal astigmatism.
In my experience, the results with toric IOLs are much better when we can confirm intraoperatively that the lens is positioned to reduce the astigmatism to the lowest magnitude.
In the U.S. Food and Drug Administration clinical trial that led to approval of the AcrySof toric IOL (Alcon), 62% of eyes were within ±0.5 D of full correction of the astigmatism. My results for toric IOLs implanted using ORA intraoperative aberrometry without VerifEye reveal that 78% are ±0.5 D, and I would expect this will improve even further with the addition of refractive data streaming.
As with all new technologies, femtosecond lasers and intraoperative aberrometry continue to evolve. Personally, I am excited about the potential for greater accuracy with these technologies — a potential that is already being realized in the form of incremental improvements that take us closer to LASIK-like results in refractive cataract surgery.