Topography-guided transepithelial ablation may treat LASIK complications

In cases with sufficient residual stromal thickness, topography-guided transepithelial ablation may be effective for LASIK flap or interface complications associated with visually disturbing irregular astigmatism and light scattering, a study found.

“If you are doing topography-guided surface ablation, especially for irregular astigmatism where epithelial remodeling has occurred, you should use the transepithelial approach; otherwise, the result may be even worse than it would be without treatment,” Xiangjun Chen, MD, first study author, said in an email interview with Ocular Surgery News.

By regularizing the corneal shape and removing the pathology that caused the irregularity in one procedure, the technique addresses complications that are often not treatable using conventional approaches, Dr. Chen said.

In the retrospective analysis, 17 eyes of 16 patients with LASIK flap or interface complications and central residual stromal thickness of at least 300 µm were treated via the iVIS Suite 1-kHz excimer laser (iVIS Technologies). Mean interval between prior LASIK and transepithelial ablation was 59.3 ± 38.8 months.

Technique, treatment

No-touch ablation was performed using the iVIS Suite, an integrated system that includes the Scheimpflug-based Precisio tomographer, pMetrics pupillometer, CIPTA topographic ablation planning software and iRES excimer laser.

The procedure is executed as a single uninterrupted ablation comprising a refractive portion that regularizes the corneal surface and a lamellar portion that “translates” the new surface into the stroma below the pathology. This approach takes epithelial remodeling into account.

“Epithelial remodeling (thickening over depressed stroma and thinning over elevated stroma) will occur in irregular astigmatism due to the irregular stromal surface and must be addressed if surface ablation is used,” the study authors wrote. “The remodeling compensates in some degree for the irregular astigmatism, meaning that the irregularity seen and measured on topography is only a part of the stromal irregularity, implying a mismatch between the epithelial and stromal surfaces.”

In other words, mechanical or alcohol-assisted epithelial removal performed using traditional techniques will result in an irregular stromal surface that does not match preoperative corneal topography.

“A topography-guided custom ablation based on topography taken on the epithelial surface will lead to error if the epithelium is removed before the laser ablation, like in conventional surface ablation techniques such as PRK, epi-LASIK, LASEK, etc.,” Dr. Chen said.

While the mechanism of epithelial remodeling has not been clarified by researchers, it could relate to the eyelid polishing effect that occurs during blinking.

Notably, a high-speed excimer laser optimized to yield a minimum ablation rate difference between the epithelium and stroma is required for the no-touch technique; otherwise, epithelial remodeling may still affect outcomes.

Results, future enhancements

At a mean of 15.9 ± 11 months postop, uncorrected distance visual acuity had improved from a mean of 20/87 to 20/25, while corrected distance visual acuity improved from 20/28 to 20/19 (P < .001). The mean corneal irregularity index decreased from 25.82 µm to 20.36 µm (P = .009), and the root-mean-square of total higher-order aberrations also decreased from 1.30 to 0.49 (P = .042).

No intraoperative or postoperative complications occurred, and eight patients said their visual symptoms had improved, while the remaining nine said they were cured. Dr. Chen and colleagues are working on improving the procedure further.

“We need to get more precise information concerning the epithelial thickness profile and the depth of the pathology to improve ablation planning,” she said. “Another possible enhancement may be a better knowledge and control of epithelial remodeling after the treatment, as well as a more precise refraction measurement amidst a high amount of higher-order aberrations.” – by Michelle Pagnani

Reference:

• Chen X, Stojanovic A, Zhou W, et al. Transepithelial, topography-guided ablation in the treatment of visual disturbances in LASIK flap or interface complications. J Refract Surg. 2012;28(2):120-126.

• Xiangjun Chen, MD, can be reached at SynsLaser Kirurgi, Lille Grensen 7, 0159, Oslo, Norway; 4745511001; email: chenxiangjun1101@gmail.com.
• Disclosure: Dr. Chen has no relevant financial disclosures.

Topography-guided ablation is an exciting technique that has consistently been improved upon over the last decade. The study authors used a transepithelial approach, which allowed them to conserve tissue and compensate for the tendency of the epithelium to fill in where there is irregularity; the epithelial filling effect creates more unpredictability when treating these irregular corneas. Some patients improved dramatically, and none experienced significant visual deterioration. All 17 said their vision was either “better” or “cured.” However, this approach is challenging; five of the 17 eyes required re-treatment. Patients should be forewarned that multiple treatment sessions may be required.

The iRES excimer laser and computer software used in this trial are not widely available, but fortunately, other systems are being developed internationally and will hopefully be accessible to U.S. surgeons soon. Studies like this one and the new technologies they evaluate are invaluable in treating patients with irregular astigmatism.

– Scott M. MacRae, MD
OSN Optics Board Member
Disclosure: Dr. MacRae is a consultant to Bausch + Lomb, Technolas and Acufocus.