The PTK solution

Resolving residual refractive error for EBMD patients: PTK offers retreatment success

After LASIK, patients with EBMD findings, such as microcysts, seen here, may benefit from PTK retreatment for residual error
Source: Ella G. Faktorovich, M.D.

Phototherapeutic keratectomy (PTK) can provide a simple, effective retreatment alternative for LASIK patients diagnosed with epithelial basement membrane dystrophy, according to Ella G. Faktorovich, M.D., director, Pacific Vision Institute, San Francisco. In a recent study published in the August 2009 issue of the Journal of Cataract and Refractive Surgery, investigators found that for both hyperopic and myopic eyes with epithelial basement membrane dystrophy (EBMD), the PTK procedure brought them very close to emmetropia.
Dr. Faktorovich’s interest in the use of PTK for such cases was spurred by a patient who had developed significant loosening of the epithelium within the optical zone close to the center of vision. “As the cornea healed, the epithelium underwent changes that were classic for epithelial basement membrane dystrophy,” Dr. Faktorovich said. “The patient ended up with a few map lines, a few microcysts, and essentially it seemed like most of her refractive error had recurred as she healed, even though we were able to get good best-corrected vision.”
When Dr. Faktorovich examined the patient, she found that the changes were minimal. “The cornea looked very clear and the best-corrected vision was pretty good, but most of the refractive error had recurred,” she said. “Knowing the pathophysiology of this disease and how the epithelium and the basement membrane thickens, I hypothesized that perhaps what happened in the areas of the cornea that were treated is that the thickened epithelium filled in the space and that’s how the refractive error came back.”

The PTK answer

Dr. Faktorovich reasoned that PTK could be the answer here. “I thought that because the patient clearly had EBMD, it wouldn’t be unreasonable to treat her for that with PTK—remove the epithelium, apply PTK pulses, and see where her refractive error ended up as she healed,” she said. Following the treatment Dr. Faktorovich found that the refractive error had gone away.
Subsequently she found herself faced with a few other similar cases. In the study, investigators looked at eight eyes of four patients with residual refractive error resulting from EBMD. The mean spherical error in the six eyes that underwent myopic LASIK was 1.75 D prior to PTK and mean astigmatism was .75 D. After PTK pulses were applied the mean spherical equivalent was reduced to –.33 D and the mean astigmatism .5 D. The mean uncorrected visual acuity improved from 20/50 to 20/20. In two eyes with hyperopic astigmatism prior to PTK the mean spherical equivalent was +4.38 D with a mean astigmatism of +3.25 D. Following PTK treatment the mean spherical equivalent decreased to +1.56 D and mean astigmatism to +2.13 D. Likewise, the mean uncorrected visual acuity increased from 20/35 to 20/27 in these retreated patients.
Dr. Faktorovich is encouraged by the results. “PTK in these patients seems to help both hyperopic and myopic refractive error,” she said. “I think this is consistent with the hypothesis that in patients with EBMD the areas that are flattened by the laser get filled up with epithelium basement membrane, extracellular matrix, etc.”

In the office

In light of the results, Dr. Faktorovich urges practitioners to keep PTK in mind for such patients. “Whenever there are patients who present for a possible enhancement because they have refractive error that is present after laser vision correction, one ought to look closely at the clarity of the cornea and the epithelium to see whether or not they have any signs of epithelial basement membrane dystrophy,” she said. This is particularly important now as patients tend to move around, initially having LASIK one place and then going elsewhere for a potential enhancement. “Patients come in and they’re now –1 or –2 D and they want to get an enhancement,” she said. “I think that before jumping in and lifting the flap and doing laser enhancements in the stroma it may be helpful to look at the epithelium first to see if there are any changes of epithelium basement membrane dystrophy.”
Recently, Dr. Faktorovich had a patient who had undergone LASIK 10 years earlier at a different facility. “He came in with myopia of –2 D, and it was clear that he had microcysts within his optical zone,” she said. “We did PTK for this patient with the elimination of his refractive error.”
Overall, Dr. Faktorovich sees the PTK approach as offering a good solution for remaining refractive error in patients with EBMD. “I think that this is very interesting and could possibly help avoid the need for lifting the flap and exposing patients to risks of flap lifting and an intrastromal procedure,” she said. “It’s a quick, simple way of addressing the problem.”

Editors’ note: Dr. Faktorovich has no financial interests related to her comments.

Contact information

Faktorovich: ella@pacificvision.org