PRK after UVA-induced collagen crosslinking yields gratifying results

Las Vegas-UVA-induced collagen cross-linking (CCL) followed by surface excimer ablation shows promise as a safe and effective technique for visual rehabilitation in eyes with keratoconus or post-LASIK ectasia, said A. John Kanellopoulos, MD, at the annual meeting of the American Academy of Ophthalmology.

At 6 months after the UVA-induced CCL procedure, the keratoconus and ectasia appeared stabilized. In 22 eyes, a reduction of the steep K by at least 2 D was seen, and 22 eyes also showed a decrease of at least 2.4 D in spherical equivalent (SE). Endothelial cell count showed a slight, paradoxical increase, possibly from discontinuing contact lens use. In most patients with an untreated, fellow affected eye, corneal pathology worsened.

"In my practice, I see no reason not to treat keratoconus with UVA CCL as a temporizing measure in the visual rehabilitation of these patients, but I caution clinicians that this modality has not been investigated in an FDA trial and is not FDA-approved," said Dr. Kanellopoulos. "My experience also shows PRK after UVA CCL provides very gratifying visual rehabilitation. However, I currently perform PRK first, followed by UVA CCL at the same visit, because I believe that approach will offer a window for re-treatment if necessary. Now, longer follow-up and additional studies are needed to see whether this technique can prevent the need for penetrating keratoplasty."

Treatment protocol

The UVA CCL light treatment is performed by first removing the epithelium as for PRK, and then instilling riboflavin 0.1% solution, one drop every 2 minutes. The light treatment is performed using a 370-nm device (Keracure, PriaVision Inc.) at an energy of 300 mW/cm² for 30 minutes.

"The goal of the ablation is not to achieve emmetropia but to normalize the cornea in order to improve BSCVA. The topography-guided treatment flattens the apex of the cone but also extends to the periphery, where it causes flattening in order to steepen the diametrically opposite side of the central cornea," explained Dr. Kanellopoulos.

He also noted using the topography-guided treatment instead of a wavefront-guided approach has several important advantages.

"The topography-guided treatment removes about 60% less tissue in these thinner corneas than a similar wavefront-guided treatment would require. In addition, it is essentially impossible to obtain reproducible wavefront maps in eyes with such irregular corneas, and therefore not possible to treat in a customized way," Dr. Kanellopoulos said.

"In our experience so far, it was usually necessary to deliver less treatment than we had planned, which indicates some nomogram adjustment is needed when ablating these rigid, cross-linked corneas," he added.

Asked about the haze that developed in a few eyes, Dr. Kanellopoulos noted that based on preclinical studies examining cytotoxicity of the UVA treatment, it is recommended that the CCL procedure be avoided in eyes with a cornea thinner than 400 μm to avoid endothelial cell damage.

"However, we have to consider some of these PRK treatments are fairly aggressive, and in our practice, a virgin normal eye treated with the same refractive parameters would also be likely to develop some haze," he said.