‘No Touch’ improves PRK re-treatments

Transepithelial method was developed to decrease haze commonly seen, as well as other complications.

NEW WESTMINSTER, Canada — Fear of complications associated with re-treatments after photorefractive keratectomy (PRK) may prevent surgeons from performing it. Donald G. Johnson, MD, developed the “No Touch” method to decrease haze commonly seen with re-treatment, as well as other complications.

No Touch ablation involves removing the epithelium and corneal tissue entirely with laser. This prevents a rough surface from occurring in re-treatment.

“It’s just as smooth as you get in a primary treatment, and you don’t get these rough edges because we make sure that we get central breakthrough, and you’re not going in too deep on the periphery to cause that,” Dr. Johnson said.

The inflammatory response clinically is no greater than what it would be in primary treatments, he said.

“We get very good results in treating haze with this technique,” he said. “There are a couple of cases where I am looking forward to using the mitomycin treatment on it, but in the majority of haze problems, we’ve had the haze removed well with this procedure.”

Haze occurs

Re-treatment incurs a greater risk of haze, unpredictability and slower re-epithelialization than primary treatment. These conditions stem from scraping, which causes a rougher surface.

“You’re capable of getting abrupt edges if you try to remove it in a plano transepithelial technique,” he said. “Increased inflammatory response can occur.”

Dr. Johnson said he uses a broad beam laser to preform a scleral plano epithelial removal. The patient self-fixates, facilitated by low room light.

Low microscope light helps the surgeon see the epithelial breakthrough and find any haze that exists.

Dr. Johnson said he always sets his ablation diameter at 6.5 mm. After he breaks through the epithelium centrally, he asks the technician to call out every 5 µm from 25 µm on as ablation moves toward the periphery. If he does not have to go deeper, he subtracts 0.25 D for every 5 µm of new ablation depth.

Since the previous treatment ends at 6.5 mm, he said he often stops at 4.5 mm or 5 mm.

“One of the secrets in doing this is to know how much spherical component to add,” he said. The nomogram depends upon the preoperative correction.

Pearls

Before re-treatment, refractive stability as defined by two readings 1 month apart with less than 0.5 D change, must be ensured, Dr. Johnson said. Also, surgeons need to ask whether the patient has restarted contact lens use.

“It’s very important to have serial refractions before you decide what you’re going to treat in an undercorrection,” he said. “Define whether it’s a normal range of regression for the treatment that you perform, the type of PRK that you perform, or is it related to haze, contact lenses or epithelial hypertrophy.”

Predictability depends upon determining whether regression is normal or not.

“Most of the fun I get out of refractive surgery now … is the analysis and the re-treatment, since that’s where you have to make your decisions to come up with the challenges that help your patients the most,” Dr. Johnson said.

Surgeons should control for accommodation, because if one eye is overcorrected it could cause a false reading. Re-treatments also need to address central islands and irregular astigmatism. This requires careful analysis of preoperative and postoperative refraction, topography and pachymetry, he said.

The postoperative regimen for re-treatment is the same as for primary treatment. Dry eyes can be one of the main causes of haze, so Dr. Johnson said he uses artificial tears as part of the postoperative regimen.

For Your Information:

Donald G. Johnson, MD, can be reached at London Place Eye Centre Inc., 918 12th St., New Westminster, British Columbia V3M 6B1, Canada; +(1) 604-526-2020; fax: +(1) 604-522-6579.