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Troubleshooting PRK
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SCRANTON, Pa.—Caring for photorefractive keratectomy (PRK) patients is a clinical challenge that may come knocking at the door of many primary care optometrists in the near future, according to one with experience comanaging both PRK and incisional keratotomy patients.
Joseph P. Shovlin, OD, part of a 24-member group of ophthalmologists and optometrists here, said, "There's considerable variation in patient response, and dealing with these variations is always going to tax the clinical skills of most practitioners."
Shovlin, one of six experts who helped write the guidelines for the initial excimer laser trials, sat on the Food and Drug Administration's Ophthalmic Devices Advisory Panel.
In an interview with Primary Care Optometry News, Shovlin reviewed PRK complications and their treatment.
Shovlin has had eight patients undergo PRK either in U.S. clinical trials or in Canada. "I think with laser surgery the complications are fewer than with RK," he said. "But unfortunately when they do occur they're just as debilitating, and in some cases even more debilitating."
Minor complications of PRK
Glare
While not as severe as with RK, debilitating glare is sometimes reported after PRK.
Pain
As with RK, nonsteroidal anti-inflammatory drugs (NSAIDs) have greatly helped reduce pain after PRK. However, the combination of an NSAID and a bandage lens, especially for more than two or three days, can lead to the development of infiltrative keratitis. If that occurs, the lens should be removed and the patient should be treated with an antibiotic-steroid combination.
Subepithelial haze
--- Visually significant reticular haze, reducing best corrected vision to 20/50 at one year.
Corticosteroids are somewhat effective for treating subepithelial haze, though their precise use has not been completely defined, Shovlin said. "Are we really modulating wound-healing as we think we are or are we just suppressing the inflammatory response, or both?"
More serious PRK complications
Decentered ablations
--- Five-millimeter ablation decentered superiorly in spite of vision correctable to 20/20. This patient complained of monocular polyopia, halos and ghosting.
Decentered ablations, Shovlin said, are the "most dreaded complication" of PRK. A decentered zone can be discovered through corneal topography.
Patients should be moved quickly to the minus side, Shovlin said. The optometrist can put the patient on pilocarpine to constrict the pupil if the decentration is not that severe. The optometrist first should conduct a careful peripheral retinal evaluation so as to avoid retinal detachment.
After pilocarpine, diclofenac (Voltaren, Ciba Vision) can be introduced to spur regression. A more drastic measure is to remove the epithelium (before six months postoperatively) in the hope that it grows back "in a less hyperplastic fashion, and not as thick, avoiding steroid usage," Shovlin said.
With decentered ablation there is often induced irregular astigmatism, so a rigid contact lens is normally the only option, he noted.
Undercorrection
An undercorrected patient can have an incisional or laser enhancement to create more flattening. (However, Shovlin said, PRK enhancements should not be made after undercorrected RK.)
Overcorrection
Treatment for overcorrection should be done quickly; after three to six months there is little that can be done, Shovlin said. Steroids should be stopped and diclofenac begun, and the epithelium can be removed at a later date. Also, an extended wear contact lens can be used to steepen the cornea.
Central islands
--- Visually significant central island created irregular astigmatism, increasing the surface regularity index on the Tomey to 2.75 (normal is 0.75 or less).
Central islands are revealed through corneal topography, and many of them disappear on their own. While corticosteroids can help eliminate many other problems, Shovlin said, they can sometimes worsen the condition. If steroids do not work, the islands need to be removed with another ablation, but he warns that "you need to be careful not to induce additional refractive effect unless that is what you want.
"Contact lenses are really a mainstay in therapy in those patients who are very unhappy," Shovlin continued. "It is fortunate that the severe complications are quite rare, because in most cases patients are going to surgery to eliminate contact lenses, so they're quite reluctant, unless things are really bad, to go back to a contact lens."
While he is not against enhancements, Shovlin said that, in general, the less surgery, the better. "The eye wasn't meant to be operated on the first time, and sometimes second and third procedures just make it worse," he said.
He advised waiting six months to a year for enhancement after PRK. "You want the healing process to be pretty much complete," he said.