In the past, refractive surgeons shied away from performing surface procedures over a LASIK flap for fear of haze, but this fear may not be as legitimate as was first thought if the treatments are conservative and surgeons take proper anti-haze measures. Some surgeons are enhancing LASIKs with PRK and LASEK with and without adjunctive use of mitomycin-C and are reporting satisfactory results in a small number of cases.
Here's a look at the pros, cons and current results with this technique.
Why Surgeons Do It
Miami surgeon William Trattler has done a small number of LASIK enhancements using LASEK, and even took part in a study of the technique. He says that, when used in the proper setting, it can yield good results and may be able to improve best-corrected acuity in some patients.
"These are usually small touch-ups, typically 1 D to 2 D of treatment," he says. "If you do it right on the surface, you're kind of etching it in, so there's no risk of the flap not being positioned perfectly right afterward, as would be the case if you did a flap relift. I think there are a number of situations in which surface enhancements will be helpful. For example, if you did a myopic LASIK and had a small flap, but the patient came back a little overcorrected, you then would need a bigger flap to do the enhancement with LASIK. So you'd either have to cut a new flap or reduce your optical zone. But, if you do the enhancement on the surface, the flap diameter isn't important."
Surgeons say other occasions where one might consider a surface enhancement post-LASIK include patients with thin flaps, flaps that might tear if a surgeon tried to lift them and suspect flaps made by other surgeons that the enhancing surgeon may not have all the surgical data on.
|Miami surgeon William Trattler has had good visual results with LASEK after LASIK. Photo: William Trattler, MD|
"We've done a few surface enhancements with adjunctive mitomycin-C for regular, uncomplicated LASIK cases in which we don't have enough residual corneal thickness to treat them, or, for whatever reason, we don't want to relift the flap or recut a flap," explains Chicago's Parag Majmudar, MD. Of course, surgeons who like this technique also say a patient with any type of flap irregularity, such as a buttonhole, is also a candidate. This is because recutting or relifting a flap in such a setting could cause problems.
Louis Probst, MD, who practices refractive surgery in Chicago and Madison, Wis., doesn't think surface enhancement is a great idea in most cases, however, and would rather just relift the flap to avoid causing corneal haze. He feels that, unless there's a problem with the flap or it's unusually thin, it can always be lifted.
"Mitomycin isn't a no-haze guarantee," he says. "We know that any time you do surface ablation on anyone who's had previous surgery, including LASIK, they have a substantially greater risk of getting haze. I don't do any surface ablation with mitomycin routinely after LASIK. I just do a LASIK enhancement by lifting the flap in a standard manner. But I will do it if there is some type of irregularity or opacity in the visual axis that may have been caused by an irregular flap or abnormal healing pattern … in my mind, just routinely doing enhancements with mitomycin over LASIK when there's a safer option isn't the smartest procedure."
If a cornea were clear and smooth, but there was a question about the integrity of the flap, Dr. Probst would recut the flap rather than lift it or do a surface enhancement. "The only time I'd go after it with a surface ablation enhancement is if I felt there would be an added benefit from removing some irregular or hazy anterior cornea."
• Enhancement data. Dr. Trattler recently participated in a retrospective, nine-practice study of LASIK enhancement with surface ablation. He contributed 10 cases to the study.
The study surgeons report on 91 eyes with an average follow-up of 13 months. At the time of their enhancement with surface ablation, 64 eyes had residual myopia with an average spherical equivalent of -1.30 D (range: -0.125 D to -4.25 D), while 25 eyes had residual hyperopia with an average error of +1.03 D (range: 0 to +3.625). Two eyes had mixed astigmatism with a SE of plano.
Fifty-four of the eyes were enhanced with LASEK, while 37 received PRK enhancements. Anti-haze measures included oral vitamin C and the use of ultraviolet-blocking sunglasses in at least half of the cases. Interestingly, only 14 of the eyes (15 percent) were treated with intraoperative mitomycin-C 0.02% at the time of the enhancement, but there were no cases of haze that affected vision or loss of best-corrected acuity.
Dr. Trattler also points out that 31 percent (27 eyes) of 86 eyes for which preop vision data was known lost some best-corrected vision after their initial LASIK, but 85 percent (23 eyes) of these had an improvement in best-corrected vision post-enhancement. Seventeen of these eyes regained their pre-LASIK best-corrected acuity, and four had best-corrected acuities that were actually better than they were before they had their LASIK. Though Dr. Trattler isn't sure why this occurred, he says some of the study surgeons believe it has to do with the enhancement eliminating flap microstriae.
"There are three main risks of the procedure," says Dr. Trattler. "These are haze, diffuse lamellar keratitis and accidental dislocation of the flap during the enhancement. To prevent haze, the key is to use all your haze-avoidance steps. Preop testing for dry eye is also critical, because I feel dry-eye patients can have delayed epithelial healing; some of my surface enhancement patients that had dry eye after surgery also had some early haze. So, I'm aggressive in identifying patients with preoperative dry eye and treating them postop." He prescribes Pred Forte q.i.d. for the first week, then switches to FML, which is tapered over six weeks.
If you're considering enhancing LASIK patients with a surface procedure, here are tips from surgeons who have done a few cases.
"I use alcohol on the epithelium for 30 to 40 seconds as if it were a LASEK, though I'm eventually going to do a PRK," says Dr. Majmudar. "I then perform the treatment and apply 0.02% mitomycin-C using a 6 to 8 mm circular Merocel sponge that's wet, but not dripping, with the agent. I place the sponge on the central cornea and leave it in place for 12 seconds, avoiding contact with the limbus or conjunctiva. Afterward, I thoroughly irrigate the cornea with about 30 cc of BSS." Since he's dealing with patients who already have an epithelial defect, which may predispose them toward DLK after surface ablation, he uses more frequent steroids for a few days postop.
One of the keys to avoiding haze may be to confine the ablation depth to the flap.
Dr. Majmudar says the procedure is limited mostly by the flap and residual bed thickness. "If you have an adequately thick flap of 120 to 130 µm, and you remove the epithelium, you've probably got 50 to 70 µm to work with without going through the flap, he says. "I think if you go through the flap, that's the most likely scenario for developing haze."
Teaneck, N.J., surgeon Peter Hersh also performs PRK with an alcohol debridement technique, and employs three anti-haze measures: 1,000 mg of vitamin C per day for one or two days preop and three months postop, mitomycin-C, and then irrigation with chilled BSS. "Though I use this method for about 5 percent or less of my enhancements, I've been delighted with the technique," he says.
Though these surgeons have only done a handful of cases so far, it seems as if the anti-haze measures and low-dioptric corrections have helped produce acceptable results. Longer follow-up of more patients will probably be necessary, though, before more surgeons feel comfortable with the technique.
"Doctors can certainly perform a normal LASIK flap-lift enhancement," says Dr. Trattler. "But, in my opinion, it's nice not to have to lift the flap."