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The refractive surgical decision tree is augmented by a new option for topography-guided custom ablation.
An algorithmic approach to surgical decisions for laser vision correction takes into account findings from topography, tomography, and aberrometry. Now this decision tree is augmented by a new option for topography-guided custom ablation.
By Cheryl Guttman Krader; Reviewed by Karl D. Stonecipher, MD
Greensboro, NC-The recent FDA approval of topography-guided custom ablation treatment (T-CAT) using an excimer laser (WaveLight Allegretto Wave Eye-Q, Alcon Laboratories) is a valuable step forward.
The treatment option allows refractive surgeons to deliver excellent outcomes to a broader patient population, according to Karl D. Stonecipher, MD, who was an investigator in the pivotal clinical trial.
“We already have great treatments for virgin corneas with wavefront-guided and wavefront-optimized ablations, and so the value of a new option depends on whether it brings something novel to the table,” said Dr. Stonecipher, medical director, TLC Greensboro and TLC Raleigh, North Carolina.
“Used out of the box without any nomogram refinements in the FDA trial, T-CAT LASIK using the [excimer laser] was associated with unprecedented refractive and visual acuity outcomes,” he said. “The results are even more impressive considering that the study population included many eyes that the investigators thought were especially well-suited for T-CAT because of corneal anatomical differences yet within normal limits for laser vision correction.”
The topography-guided ablation is determined by proprietary treatment planning software using data acquired with the WaveLight Allegro Topolyzer. Treatment accuracy is assured with the laser’s advanced platform for eye-tracking and registration (NeuroTrack).
The FDA clinical trial included 247 eyes that were treated for myopia with or without astigmatism. Analyses of data collected at 3 months showed uncorrected visual acuity was 20/20 or better in 93% of eyes, 20/16 or better in 69%, and 20/12.5 or better in 32%. Best spectacle-corrected visual acuity was 20/40 or better in all eyes and improved by at least 1 line from preoperative in 30% of eyes.
Mean postop MRSE was 0.06 D and stable throughout follow-up to 12 months. Nearly all patients, 98%, said they would undergo the topography-guided ablation again.
Based on his own research investigating outcomes after LASIK, Dr. Stonecipher said he has been a firm believer that not all patients need to undergo a wavefront-guided procedure. Results of a randomized study he conducted with Guy Kezirian, MD, showed that eyes without significant higher-order aberrations (HOAs) can achieve equally good results with a wavefront-optimized procedure [J Refract Surg. 2008;24:S424-430].
Therefore, to guide the surgical decision, all patients undergo a full diagnostic evaluation that includes topography, tomography, and wavefront aberrometry. Generally, only patients with preoperative root-mean-square HOAs of 0.35 to 0.4 μm or higher are considered candidates for a wavefront-guided procedure, assuming that it was possible to capture a good wavefront.
Patients with an “odd looking” cornea-i.e., an eye with an asymmetric bowtie pattern that still fits topographic eligibility criteria for LASIK-are considered the ideal example of a patient for T-CAT. However, Dr. Stonecipher noted that in the FDA trial, many patients with completely normal corneas were treated and had an excellent outcome.
“T-CAT ablation profiles create large uniform optical zones, which I think added to the outstanding results we saw in this FDA trial,” he said.
“In treating these patients with a topography-guided ablation, we have the opportunity to fully replicate the cornea in a way that was not possible before and provide them with better outcomes.”
He noted that one downside of the T-CAT treatment is that it removes more tissue than a wavefront-optimized ablation.
Outside the United States, T-CAT is being used to rehabilitate eyes with poor outcomes. In addition, several investigators are using T-CAT in conjunction with cross-linking of the cornea for keratoconus and corneal ectasia.
“It is important to note that this is off-label,” Dr. Stonecipher said.
Dr. Stonecipher also underscored that regardless of the type of ablation, the outcome of any LASIK procedure depends on the condition of the ocular surface, the flap-making tool used, and the postoperative management received.
“Noise going in leads to noise going out, and so if you are going to do a perfect treatment, you need to have a perfect ocular surface,” Dr. Stonecipher said.
“The reality is that most patients seeking LVC have challenges with their vision because of an ocular surface condition. Furthermore, results from the WaveLight T-CAT trial and other studies show that patients who had dry eye before LASIK are likely to have dry eye postoperatively. Capturing accurate diagnostic information for guiding the ablation and minimizing postoperative complaints depends on the patient having good ocular surface health.”
Findings from an analysis of data from more than 25,000 eyes provide support for Dr. Stonecipher’s belief that use of a femtosecond laser for flap creation will afford superior results. Compared with a mechanical microkeratome, use of the laser minimizes surgically induced HOAs and the chance for a postoperative enhancement, he explained.
Regarding postoperative management, Dr. Stonecipher emphasized the importance of patients using good quality products to minimize inflammation and the potential risk of infection in the current refractive patient population.
Karl D. Stonecipher, MD
Dr. Stonecipher is a consultant to Alcon Laboratories.
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