Long-term corneal stability still a challenge for LASIK surgeons, physicist says

SAN DIEGO, Calif. — With the advent of customized ablation, many ophthalmologists believe they have found the holy grail of refractive surgery. But the promise of wavefront-guided laser ablation will not be fully realized until researchers gain a more complete understanding of corneal biomechanics, according to a pioneer of excimer laser corneal research.

John Marshall, PhD, delivered the Charles D. Kelman, MD, Innovator’s Lecture on the topic of “Wavefronts and Biomechanics” here at the American Society of Cataract and Refractive Surgery meeting.

Dr. Marshall recalled that pioneers of laser refractive surgery faced questions about how much corneal tissue could be removed before corneal instability occurred. Early work in photorefractive keratectomy (PRK) resulted in variability of outcomes, which were only improved with the introduction of corneal topography and the refinement of laser beam and spot sizes, he said.

Dr. Marshall, one of the organizers of the First International Workshop on Laser Corneal Surgery, noted that the introduction of LASIK also marked a major breakthrough in reducing, and sometimes eliminating, postoperative pain and haze.

But the biomechanics of LASIK, in comparison to PRK, suggest that the microkeratome-based procedure causes more corneal weakening, he said.

The cornea is made up of collagen filaments arranged in grids not unlike the steel skeleton of a building or car tire, according to Dr. Marshall. When tissue is removed in PRK, he said, the surgeon cuts through 5 million of those fibers. In LASIK, by comparison, 232 million fibers are disrupted, he said.

The mechanical system of the cornea is weakened by the microkeratome cut even before the laser ablation, which induces its own microabrasions, Dr. Marshall noted.

“Certainly, at the moment, it seems that LASIK is less stable over the long term than surface procedures,” he said. “This is a major problem if we think we’re really going to use wavefront to the level we want to use it.”

The real benefit of wavefront technology to date has been to enhance or correct previous surgeries, he added.

He challenged future innovators to make sure that “wavefront technology has [not] gotten ahead of the biology.”