August 2012

 

COVER FEATURE

 

Refractive challenges and innovations

Addressing the post-RK hyperopic shift


by Michelle Dalton EyeWorld Contributing Writer

   
RK compromised cornea

A post-RK compromised cornea Source: Mark Packer, M.D.

Surgical options remain limited, and none can reverse the continued hyperopic progression. But newer techniques may be able to offset the diurnal fluctuations

Very few uncomplicated refractive surgeries result in unhappy patientsunless the patient has undergone radial keratotomy (RK). In the post-RK eye, a high percentage (upward of 40%) has hyperopic shifts. "The most difficult cases to manage are patients with previous RK and progressive hyperopia," said Eric D. Donnenfeld, M.D., clinical professor of ophthalmology, NYU Medical School, New York. "It's extremely common with RK and [has] a direct association with the number of incisions the patient underwent." RK is a procedure that gained popularity in the early 1990s; surgeons would make radial incisions (typically four or eight incisions per eye) that resulted in a flattened cornea. Retreatments with RK for highly myopic patients resulted in some corneas receiving up to 32 incisions. Unfortunately, it wasn't until the mid-1990s that published studies alerted surgeons to the long-term issues with RK, said Parag A. Majmudar, M.D., associate professor of ophthalmology, Rush University Medical Center, Chicago, and in private practice, Chicago Cornea Consultants Ltd.

"RK never stops," he said. "The incisions continue to flatten the cornea and that's what causes the hyperopic shift, and it's progressive. These patients are miserable most of the time."

John A. Vukich, M.D., partner, Davis Duehr Dean Center for Refractive Surgery, Madison, Wis., started performing RK in the early 1990s but had abandoned it by 1995. "Many of the RK patients who were in their early 30s at the time of surgery are now in their 50s. Most of them became presbyopic earlier because of latent hyperopia post-RK. Almost every one of them is back in spectacles and few are happy with their current vision," he said. "Unfortunately, these were patients we thought we were helping at the time."

Complicating matters further for physicians and patients alike is that patients can have diurnal fluctuations up to "a couple of diopters of difference," Dr. Donnenfeld said. He added many of these corneas are incredibly flat and cited Ks as low as the mid-30s in some cases. Ideally, he said, the goal is to make these patients emmetropic in the morning and myopic in the evening rather than having them plano in the evening but hyperopic in the morning.

"Hyperopia of RK is the gift that keeps on giving," Dr. Donnenfeld joked.

Providing better vision

The biomechanical stability of the cornea has been lost in a post-RK eye, Dr. Majmudar said. "I tell patients we can remove the hyperopia today, but in 6 months or a year that might change. If the cornea continues to get more ectatic in the mid-periphery, the hyperopia will return."

Surgeons basically have three options, he said: LASIK, PRK, or (if age appropriate) cataract surgery. Creating a LASIK flap after RK can result in irregular astigmatism because of potential flap issues, so Dr. Majmudar doesn't recommend it. "RK and LASIK are incompatible," Dr. Vukich said. "The hyperopic shift is a corneal problem, and placing horizontal transecting incisions into vertical incisions is a recipe for disaster." When he did perform LASIK on these eyes in the past, Dr. Donnenfeld said some patients had issues with the RK incisions splitting, creating a "pizza pie-like appearance." If he can obtain wavefront aberrometry, he's comfortable performing PRK but offered a few pearls.

First, he said, if there are epithelial inclusion assists within the incisions themselves, it indicates the incisions are spreading. He prefers to clean out the incisions with a Sinskey hook and suture them closed with non-biodegradable sutures (such as 10-0 prolene). Suturing will hold the incisions together and, by tightening, may result in reversing some of the hyperopia and astigmatism that's been caused in the area. He also uses mitomycin-C for 30 seconds (0.02 mg/mL) instead of the typical 12 seconds in surface ablation.

"I'd rather steepen the cornea than do a clear lens exchange," he said. "I think the optics with a steeper cornea are better for these patients."

Dr. Vukich will try to leave patients in spectacles if they have a minimal correction and functional vision; otherwise he prefers to perform refractive lens exchange (presuming no irregular astigmatism/ higher order aberrations). "I'll aim to leave them a little myopicmaybe a 1 or sobecause they'll continue to have a slow hyperopic shift toward emmetropia," he said. "They'll need glasses for distance, but patients appreciate the improved near vision." Likewise, he's "hesitant" to correct astigmatism with a toric IOL, saying results are less predictable.

"We have to tell these patients that 'perfect' isn't possible. We can try to improve their vision, but they're not going to have the vision they did in their 20s," he said. Most RK patients have been living with variable vision and advancing hyperopia "for at least a decade," so while they may not be happy about the situation, "they've learned to cope with their vision," he said.

Dr. Donnenfeld "highly recommends" intraoperative aberrometry in clear lens exchange patients, especially in cases of high hyperopia, because predicting IOL powers is "next to impossible" after the keratometry changes. Dr. Vukich also recommended using a scleral tunnel incision to minimize induced corneal astigmatism. "You want to tread as lightly as possible to avoid stretching," Dr. Donnenfeld said.

Following cataract surgery, it's not uncommon to have an immediate hyperopic shift of up to 2 D, "but don't be dissuaded by that," since the patient can go plano after 2 months or so, Dr. Donnenfeld said. Because of the significant higher order aberrations associated with these patients, he recommended using a negative or zero aberration lens.

CXL?

Post-RK article summary

Dr. Majmudar said a newer, but somewhat controversial, potential treatment for these patients might be corneal collagen crosslinking (CXL), which "may improve the biomechanical stability of the cornea like we see in keratoconus." Early results seem to indicate CXL may help alleviate the diurnal fluctuations in vision for these patients. No studies have shown CXL can change the hyperopic shiftyet, Dr. Donnenfeld said. "I've done CXL on about 20 patients with previous RK and found in patients with fewer incisions it's eliminated the diurnal fluctuations, but not so in those who had 8 or 16 incisions. In that latter group, however, CXL did reduce the magnitude of the fluctuation." More importantly, no one's vision was adversely impacted after undergoing CXL, he added.

For Dr. Vukich, the early anecdotal results are promising, but "it's too early for any projections forward." "If you've done PRK, done cataract surgery, tried CXL, and the patient is still having issues, the only remaining option may be transplant," Dr. Majmudar said.

Editors' note: The doctors mentioned have no financial interests related to this article. Dr. Majmudar is an investigator for the CXL Group.

Contact information

Donnenfeld: 516-446-3525, eddoph@aol.com
Majmudar: 847-275-6174, pamajmudar@yahoo.com
Vukich: 608-282-2000, javukich@gmail.com