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Microwave thermal keratoplasty significantly reduced myopia
Adjunctive cross-linking may maintain corneal stability and preserve myopic correction, author says.
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Despite some regression, a novel thermokeratoplasty procedure safely and predictably corrected myopia and improved distance visual acuity, according to a study.
Ugur Celik, MD, and colleagues explored microwave thermokeratoplasty as an alternative to LASIK and PRK. The procedure involves applying microwaves to the superficial corneal stroma and altering the curvature of collagen fibers without severing them.
“The study showed that the microwave thermokeratoplasty procedure provided safe and initially predictable results. Although the effect regressed over time, it opens the possibility for adding an adjunctive procedure, such as cross-linking, to maintain the result,” Celik told Ocular Surgery News in an email interview.
Celik cited the fact that there is no cutting of the collagen fibrils, and thus, no weakening of the cornea, as one of the principal advantages of the procedure.
Ugur Celik
Additionally, “it is anticipated that patient acceptance, particularly for those seeking low-diopter corrections, will be much higher than for a standard surgical intervention.”
The study was published in the Journal of Cataract and Refractive Surgery.
Patients and protocols
The prospective clinical trial by Celik, Omer Faruk Yimlaz, MD, David Muller, PhD, and colleagues included 33 eyes of 33 patients with a mean age of 27.3 years who underwent microwave thermokeratoplasty for myopia.
Mean attempted correction was –3.13 D (range: –1.25 D to –5.75 D). Microwave thermokeratoplasty was performed with the Vedera KXS system (Avedro).
Eyes were examined preoperatively and at 1 week and 1, 3, 6 and 12 months postoperatively. Investigators assessed logMAR uncorrected and corrected distance visual acuity, slit lamp biomicroscopy, tonometry, corneal topography, central corneal pachymetry, endothelial cell count and fundus images.
The primary outcome measure was change in uncorrected distance visual acuity.
Preoperative mean uncorrected distance visual acuity was 0.76, mean corrected distance visual acuity was 0, mean keratometry value was 43.9 D and mean manifest spherical equivalent was –2.92 D. Mean central corneal thickness was 556 µm, and mean endothelial cell density was 2,836 cells/mm2.
Results and conclusions
Study results showed that mean uncorrected distance visual acuity improved to 0.17 at 1-month follow-up, which indicated a significant difference (P < .001).
Correction was within 0.5 D of the target in 85% of eyes.
“The 1-month predictability of the first 31 patients was remarkably good, with almost all patients being within ±0.5 D. This was much better than the initial results from PRK in the early 1990s. It is reasonable to think that this accuracy could be further improved, in particular with focus on the low-diopter myopes,” Celik said.
A significant mean regression of 0.57 (P = .001) was identified at the 3-month follow-up; however, the improvement in uncorrected distance visual acuity remained significant.
“We don’t know the exact cause, but it appears that over time the collagen returns to its pretreatment shape and form,” Celik said. “The most likely way to stabilize it would be through the use of corneal cross-linking. Corneal cross-linking has been shown to stabilize pathologically weak corneas, and it may be possible to find a corneal cross-linking treatment regimen that could significantly extend the life of the procedure.”
Mean endothelial cell density was 2,732 cells/mm2 at 12 months; the reduction in mean endothelial cell density from baseline was insignificant.
Results showed marked improvements in corneal shape, Celik said.
“In addition to a central flattening of the cornea, there was also a symmetrization and retention of the cornea’s natural prolate shape,” he said. “In the case of irregular corneas, the treatment tended to smooth out the irregularities.”
Further study of thermokeratoplasty in treating keratoconus is ongoing, Celik said. – by Matt Hasson