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Corneal ring segments offer patients quick visual recovery

Issue: January 1998

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KANSAS CITY, Mo. - Veteran refractive surgeon Daniel S. Durrie, MD, in practice here at the Hunkeler Eye Clinic, offers the gamut of refractive surgery procedures, but none, said Dr. Durrie, offers results as rapidly as the Intrastromal Corneal Ring Segment (ICRS).

"The most impressive aspect of this procedure is that the patients see so well so fast," Dr. Durrie said. "I used to think that the intrastromal corneal ring was going to be unique just because it can be removed and its effects can be reversed, but it turns out that it offers the highest quality of vision early on of any procedure - photorefractive keratectomy, laser in situ keratomileusis (LASIK), radial keratotomy - available for myopia," he said.

The ICRS, manufactured by KeraVision in Fremont, Calif., are twin semi-circles of optically clear PMMA that are threaded into the corneal stroma, outside of the optical zone. Varying thicknesses of the device correlate with reduction of between 1 D and 5 D of myopia. The device can be removed, if results are not satisfactory, making it completely unique to the refractive surgery realm.

Dr. Durrie is one of several investigators in a Food and Drug Administration clinical trial of the ICRS, now in phase 3. He told Primary Care Optometry News he has high expectations for the device. "I think it is going to have a major place in low myopia surgery, but patients really like the idea that it is removable and reversible. As surgeons, we don't really care how easy it is to remove or exchange," he said, "because we never want to have to re-do a procedure."

Topical anesthesia used

--- Intrastromal Corneal Ring Segments are twin semi-circles of optically clear PMMA that are threaded into the corneal stroma.

The rings are implanted under topical anesthesia. Dr. Durrie makes a 1.8-mm long incision that is ¾ mm in depth, which forms a pocket in the stroma. The clinical protocol requires that the incision be sutured, but Dr. Durrie suggested that it is probably not necessary in the long-term. The procedure is very fast, he said, averaging between 5 and 8 minutes. "It is a very straightforward procedure," said Dr. Durrie. "The surgical skills necessary are similar to those used to fashion a good phacoemulsification wound."

Patients with myopia below 5 D and low or no astigmatism are ideal candidates for the ICRS. "It is very easy to identify these patients. They are the same ones who are wearing disposable soft contact lenses," Dr. Durrie said.

The procedure completes the menu of refractive surgery procedures he offers. "Most of my LASIK patients are toric patients, or patients with high myopia who are intolerant of contact lenses, so the ICRS has been very complementary to my practice."

Postop treatment, complications

Visual recovery is rapid and stable. "The best-corrected visual acuity is better 1 day postop with the ICRS than we have seen with any other procedure," Dr. Durrie said. "That may be because there isn't any surgery in the center of the pupil."

Dr. Durrie prescribes antibiotics - either Ciloxan (ciprofloxacin HCl, Alcon) or Ocuflox (ofloxacin, Allergan) - for 1 week. "The main thing you want to avoid is infection, and that just takes good surgical technique at the time of surgery," he said. "I prescribe the antibiotic postoperatively because the ring is an implantable material, so I want to be sure that none of the normal flora that lives in the conjunctiva ends up entering the channel where I've implanted the ring."

Dr. Durrie's technique has changed minimally during the time that he has been working with the ICRS. His procedure originally induced a small amount of astigmatism, he said, but as the algorithms and procedure were refined, the amount of induced astigmatism has decreased.

"I think the ICRS procedure parallels the advancements in phacoemulsification," he said. "We now do less wound manipulation and, therefore, we have seen a significant drop in the amount of astigmatism that is induced from the procedure. In the past, if there was a lot of wound manipulation or if the suture was tied too tight, a lot of astigmatism could be generated just by the surgery itself, and just like cataract surgery, having a good wound construction and minimal tissue manipulation ends up with more predictable results and less chance of inducing astigmatism."

Low rate of ring exchange

--- Varying thicknesses of the device correlate with reduction of between 1 D and 5 D of myopia.

Though the reversibility of the procedure is a significant selling point, the number of instances in Dr. Durrie's experience when removal was in order is very limited. "The percentage of rings that have been removed or exchanged is extremely small because we've learned which thickness ring to put in which patient," he said. "The rate of removal was a lot higher when we just started out because we really did not know what amount of corneal change each ring thickness would induce."

Adjustability, rather than reversibility, is the ICRS's strong suit, he suggested. "There isn't any change in the refraction after a week or so, so we're putting the ring in and if someone doesn't get exactly what he or she wants, then we'll change it," Dr. Durrie said. "Adjustability is really the key to it."

Durrie's associate Brian S. Boxer Wachler, MD, of the Kansas University Department of Ophthalmology, recently reported on the Hunkeler Eye Clinic's ICRS clinical trials at the International Society of Refractive Surgery (ISRS) annual meeting. Dr. Boxer Wachler explained to Primary Care Optometry News that patients over 21 years of age were eligible for the study; the main criteria for eligibility among the 50 patients on whom Dr. Durrie has 1-month follow-up is that they had a healthy eye and stable refraction preoperatively.

The most important criteria when patients are choosing a refractive surgery procedure are low pain and fast visual recovery, and the ICRS procedure offers both, Dr. Boxer Wachler said. One day postoperatively, 26% of the 50 patients were 20/16 or better; 54% were 20/20 or better; 76% were 20/25 or better; and 96% were 20/40 or better. At 2 weeks, 50% were 20/16 or better; 72% were 20/20 or better; 84% were 20/25 or better; and 94% were 20/40 or better.

At 1 month, 63% were 20/16 or better; 82% were 20/20 or better; 88% were 20/25 or better; and 98% were 20/40 or better. "These results," said Dr. Boxer Wachler, "suggest that a need for additional spectacle correction is minimal."

A few patients in the study, according to Dr. Boxer Wachler, who were intended for monovision correction, were purposefully undercorrected with satisfactory results.

For Your Information:

• Daniel S. Durrie, MD, and Brian S. Boxer Wachler, MD, may be reached at the Hunkeler Eye Clinic, 4321 Washington, Suite 6000, Kansas City, MO 64111; (816) 931-4733; fax: (816) 931-9498; e-mail: dan.durrie@rssinfo.com. Dr. Wachler has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any company mentioned. Dr. Durrie is a paid investigator, with no stocks or royalties, for KeraVision.For more information from KeraVision about the ICRS, contact Mick Taylor at (510) 353-3000.