Topographic neutralizing technique useful in managing corneas aberrated after LASIK, PRK

June 15, 2009

The custom topographic neutralizing technique seems to be a promising alternative for treating patients with aberrated corneas after refractive procedures. The procedure is performed using a proprietary topographically guided excimer laser (Allegretto Wave Eye-Q, Alcon Laboratories [formerly WaveLight]) and corneal topographer (Allegro Topolyzer, Alcon Laboratories [formerly WaveLight]).

Key Points

"Correcting highly aberrated corneas can be difficult," he said. "TNT offers an alternative treatment to wavefront-guided treatments for patients who underwent a refractive procedure with less-than-optimal visual results such as decentered optical zones or small optical zones."

Dr. Holland is in private practice with co-author David T.C. Lin, MD, FRCSC, at the Pacific Laser Eye Centre, Vancouver, and a clinical professor of cornea at the University of British Columbia, Vancouver. Dr. Lin is clinical associate professor of ophthalmology, Department of Ophthalmology, University of British Columbia.

Drs. Holland and Lin evaluated the effectiveness of TNT for treating aberrated corneas after laser refractive surgery. A proprietary topographically guided laser (Allegretto Wave Eye-Q, Alcon Laboratories [formerly WaveLight]) was used to treat 115 patients, 67 of whom had decentered optical zones with irregular astigmatism and 48 with small optical zones. The laser system included a corneal topographer (Allegro Topolyzer, Alcon Laboratories [formerly WaveLight]). All patients had undergone a previous LASIK or PRK procedure.

Dr. Holland said the treatment has four stages:

"The treatment is complex because we have to anticipate any induced changes," he said.

During the study, the patients underwent measurement of preoperative and postop uncorrected visual acuity (UCVA), best spectacle-corrected VA (BSCVA), refraction, topography, centration relative to the pupil center, and change in the monodioptric optical zone. The study also evaluated the predictability and safety of the technique.

Dr. Holland reported that of the 67 patients treated for a decentered optical zone from 0.9 to 0.3 mm, 76% had 20/20 UCVA, 76% had 20/25, 94% had 20/40, and 100% had 20/80. In this group, 5% gained two or more lines of BSCVA after TNT, and none lost two or more lines.

In the 48 eyes treated with TNT for small optical zones, an increase occurred in the central monodioptric optical zone from 3.9 to 5.6 mm (p < 0.01). All patients had been symptomatic before surgery, and 81% were asymptomatic after surgery. Twenty-one percent of eyes had an improvement in vision of at least one line; 75% of patients had no change in BSCVA, and 6% lost one line of vision. All eyes had improvement in the degree of astigmatism from 1.25 to 6.75 D. In this group, 63% had a UCVA of 20/20 and 94% had 20/40. The predictability of the procedure was 94% ± 1 D, according to Dr. Holland.

"All patients were symptomatic before surgery with one or more symptoms such as halos, glare, poor night vision, image doubling, blurred or hazy vision, and starbursts," he said. "Most of the study patients, 81%, in both groups had an improvement or resolution of the preoperative condition. The remainder had no improvement, refractive error, nor regression."

Challenges of irregular astigmatism

Dr. Holland said that challenges in treating patients with irregular astigmatism exist.

"The treatment planning is difficult," he added. "Correction of the induced refractive error demonstrates the value of TNT in limiting the need for a second treatment for the changes induced by the plano topographically guided treatment. Patients need to have realistic expectations."

TNT currently may be the best surgical option, for example, when wavefront capture is poor, he said.

"Treatment of highly aberrated corneas with topographically guided ablation using the [proprietary] platform and custom TNT has the potential to resolve or improve symptoms in patients with complications of laser refractive surgery," Dr. Holland continued. "The safety profile is acceptable for patients with small optical zones and re-treatments for decentered ablation, but treatment planning is challenging due to the induced refractive error from the topographically guided treatment."

TNT is not yet approved by the FDA.