Refractive surgeons debate RK, PRK, LASIK at Academy meeting

Issue: February 1996

NEW ORLEANS—Joseph P. Shovlin, OD, of Northeastern Eye Institute, Scranton, moderated a refractive surgery panel presentation here at the American Academy of Optometry's annual meeting. Shovlin was one of six experts who wrote the guidelines for the initial excimer laser trials as a member of the Food and Drug Administration's Ophthalmic Devices Advisory Panel.

Participants included:

Richard L. Lindstrom, MD, Minneapolis, whose practice consists of corneal, refractive and cataract surgery and glaucoma. Lindstrom, who supports comanagement of refractive surgery, is President of Eye Health Network of Minnesota and North Dakota, and is on the national board of Eye Health Network.

Henry Haley, MD, of New Orleans, is part of a private practice group focusing on general ophthalmology as well as cataract care.

Daniel S. Durrie, MD, of Kansas City, was the first surgeon in the country to perform photorefractive keratectomy (PRK) after U.S. Food and Drug Administration approval. He performed 100 PRKs in the first 4 weeks after approval.

Marguerite McDonald, MD, was the first investigator to perform PRK. McDonald is director of the Refractive Surgery Center of the South at the Eye, Ear, Nose and Throat Hospital, New Orleans, and medical director of Autonomous Technologies.

Joseph P. Shovlin, OD: What causes late-presenting haze?

Richard L. Lindstrom, MD: You want all your patients to get haze, then you want to see it go away. Late-onset haze is probably an abnormal response of the ablated eye to an insult.

We found that if we treat these patients aggressively with steroids for about 2 weeks, and then taper down the steroids, most of them get better. If they don't get better, they need to be retreated.

Shovlin: Can we avoid this problem by not removing Bowman's layer?

Lindstrom: We can't avoid this problem with PRK.

Marguerite McDonald, MD: In addition to an insult to the ablated eye, we've had patients who have undergone a lot of metabolic stress—such as pregnancy, change in lifestyle—and then experienced late haze. But this is just a hunch, at this point.

Daniel S. Durrie, MD: Placing a contact lens on the eye during the healing phase will definitely give you haze and regression. If somebody has a lot of haze you should suppress their healing, keep them well lubricated, keep them from irritating the eye.

I believe laser in situ keratomileusis (LASIK) gets rid of a lot of this. I'm a strong proponent of LASIK because of it.

Lindstrom: Some data suggest that patients with hay fever conjunctivitis or allergic conjunctivitis who are treated during their bad season don't do as well. Also, patients must continue with eye wear even after PRK, such as UV-absorbing sunglasses to protect the eye.

Shovlin: What do you do with eccentric ablation?

Durrie: This should never happen. The surgeon must put the ablation in the center of the eye. It's pretty much impossible to fix.

We can do some things to try to move the ablation over by blending the zone, but if the patient is already hyperopic, you'll just make the cornea flatter.

Optometrists who are starting to refer cases must make sure the person they're referring to has taken the courses, has good technique and doesn't have this happen with their first few cases, because you'll be stuck with a really unhappy patient.

McDonald: For the hyperopia you can try several things. A soft lens will rub on the ablation and perhaps induce healing so the hyperopia will go away. If patients think of it as a temporary and therapeutic procedure, they'll usually go back into their lens. Try that for a month. If that doesn't work, try Voltaren (diclofenac, Ciba), four times daily for a month.

If that doesn't work, I scrape. Scraping makes the keratocytes wake up and produce more collagen, and the whole cornea wakes up and continues to heal.

If all else fails, do a good depressed peripheral retinal exam and make sure there's no pathology, and put the patient on weak pilocarpine, 0.5%-2% four times a day, titrating the doses. This will induce myopic shift in a young enough patient, and the optical aberrations from decentration will be much enhanced by the pinhole effect of the pupil.

Lindstrom: This happened to one of my first 10 patients. I ended up using the phototherapeutic keratectomy mode on the excimer laser with a small spot size, blending off that edge.

If you do peripheral laser, you can steepen the cornea a bit. You could also treat this with a hyperopic PRK, although we don't have that in the United States.

Henry Haley, MD: I've read that some surgeons have recommended going the same distance in the opposite meridian and doing another decentered ablation in order to smooth the center out. Would any of you ever recommend this?

Durrie: I've taken care of a case like this, and I took the steps Dr. McDonald listed to stimulate healing to fill in the hole.

I managed to return the patient to myopia, and then I did a re-centered ablation. That did work to get rid of the halos and did not make the patient hyperopic.

Shovlin: What are our options for treating a patient with overcorrected radial keratotomy (RK) and consecutive hyperopia?

Lindstrom: If you're comanaging a patient and you see it early—at a week or two—and they're more hyperopic than makes you comfortable, stop any steroids, use topical hypertonic drops, begin—as early as a month—0.5% pilocarpine four times daily and increase that to 1%-2% and treat for 4-6 months with miotics. Miotics potentially help a little bit with pseudoaccommodation, creating a miotic pupil with increased depth of focus, but they also seem to induce wound healing, either directly or indirectly by being an irritant to the eye.

If you see someone at 6 months, or someone who had surgery 12 years ago, and they have a progressive hyperopic shift, I believe in compression suture techniques. They've worked well for me for a lot of patients. I would strongly recommend extreme caution with automated lamellar keratoplasty over previous RK.

Shovlin: Why is it that we seem to be able to do a touch-up with RK after PRK, yet the results with the opposite, RK followed by PRK, are not very good?

Durrie: If you use a laser over any cornea that's had any surgery, the patient is more likely to be a Type III healer and get haze. That doesn't mean it can't be done, and with the smoother generation lasers we're seeing it can be done. But you'll have to watch their wound healing.

Lindstrom: Some surgeons are recommending for myopia greater than -7 D, which is the current approval with the Summit laser, to do a maximal RK, let's say for a -12 D, then let it heal, then do a PRK over it.

I would strongly discourage you from considering that for your own patients. The complication rate is much higher. Plus, you have all the complications of RK as well as PRK, only worse than average. That's not a good approach. A mildly undercorrected PRK does respond well to an RK, however.

I would also agree with Dr. Durrie, that with the occasional RK patient from years ago who is undercorrected and very unhappy, we've done well with a larger optical zone PRK. Another thought is a transepithelial ablation, which seems to reduce the tendency for haze.

Shovlin: Is there a greater prevalence of cataracts after RK?

Lindstrom: We don't think RK causes cataracts, we also don't think PRK causes cataracts. Long-term steroid use, as with PRK, could play a role in cataract formation.

Shovlin: How do we calculate the power of the intraocular lens (IOL) following RK?

McDonald: The best way is with the average corneal power (ACP), which is an estimation taken from your topography picture. Studies have indicated that after both good and bad RK, if you use the standard K readings to calculate the IOL as opposed to the ACP, you're, on average, 1.25 D off.

With an optimal PRK, you're very close to perfect: 0.5 D to 1 D maximal off. With a suboptimal or decentered PRK, you can be 3.25 D off. It is better, in that case, to take a topography picture and use an average corneal power, which is a weighted average taken over the entrance pupil.

Durrie: Don't be surprised if somebody has cataract surgery after RK and they get a temporary hyperopic shift of 2-3 D that lasts a month or two. That's normal after an RK to go hyperopic for a while and come back down. The surgeon should not rush in and exchange an IOL. This is one of the reasons RK may have another black mark against it. It is quite difficult to calculate the IOL power after an RK. With a PRK it will be much easier.