feature
Conductive Keratoplasty: Effective, Safe Results for Presbyopia
One surgeon discusses his technique and results with this procedure.
BY RACHEL M. RENSHAW, EXECUTIVE EDITOR

Conductive keratoplasty, known as NearVision CK (Refractec, Irvine, Calif.) was introduced to the refractive market in April 2002 and since that time, has become a mainstay in many surgeons' practices. NearVision CK uses a radiofrequency pulse applied with a probe tip to heat and shrink the collagen on the periphery of the cornea, thus steepening the angle to improve near visual acuity. The CK procedure has been compared to laser thermal keratoplasty (LTK), which also shrinks collagen, but instead of relying on laser energy applied to the cornea, CK uses radio frequency energy to penetrate deeper into the corneal stroma for a longer-lasting effect than is achieved with laser energy on the surface.

NearVision CK provides an alternative for patients with presbyopia who wish to be spectacle-free for seeing up close but do not relish an invasive procedure such as hyperopic LASIK, PRK or IOL implantation. H.L. "Rick" Milne, M.D., president of the Eye Center, PA, in Columbia, S.C., has been using NearVision CK for hyperopic correction on his patients with presbyopia for about 4 years. This article will discuss his clinical experience with the procedure including patient profile, technique and overall results with CK.

Dr. Milne says that the perfect patient for a NearVision CK procedure is the emmetropic presbyope who needs glasses for reading and other similar near vision activities. "This is good for any patient who needs up to 2.25 D to 2.50 D hyperopic correction." Dr. Milne continues, "The other patients who have success are psuedophakic emmetropes and those who have had LASIK or PRK prior to becoming presbyopic — who have been made emmetropic by surgery and now have lost their near vision."

In his practice, Dr. Milne has found that when providing the available options to his patients, they usually choose the non-invasive CK procedure because it offers the benefits of refractive correction with few risks. He counsels them frankly so that they understand the procedures available to them.

"I tell patients they have two choices: we can reshape their cornea or we can replace their lens. I explain that the first option doesn't address the pathology of presbyopia, wherein the lens progressively loses the ability to focus. We're essentially reshaping that corneal curve power to their cornea, not stopping the process of aging. With either LASIK or CK, the procedure is temporary, but CK is the safer and the less expensive of these two options," Dr. Milne says. "I also tell patients, 'eventually, you will probably have a lens procedure but it will need to be performed in both eyes, is expensive, and carries more risk because it's a surgical procedure.'"

Most patients will choose the CK procedure, he says, because they would prefer not to undergo a premature lenticular procedure, and the cost of a CK procedure is reasonable at $1,500 per eye. Moreover, the CK procedure to correct presbyopia is performed in one eye only — inducing mild to moderate myopia in the non-dominant eye to provide for near vision while preserving the distance vision in the dominant eye. Thus, the patient achieves good results with the reduced cost of a one-eye treatment.

Those who are not candidates for CK include patients with autoimmune disease, such as rheumatoid arthritis, where corneal health is compromised. Additionally, says Dr. Milne, this is not a procedure for patients with steep K-readings or thin peripheral corneas.

He also advises that patients who have been unhappy with monovision should not be treated with CK. "For patients who I'm going to be giving more than a 1-D effect, I always do a contact lens trial to be sure that they're going to be happy with monovision," Dr. Milne says.

Surgical Pearls

When Dr. Milne began performing CK, he noticed that his results for the first 2 years were not on target with the preoperative goals and did not reflect the results that were seen with the FDA clinical trials. He soon learned from experience that compression was the issue in the varied responses from the eyes after the procedure.

"Fortuitously, I had a patient where I didn't cause as much pressure on the cornea and got a dramatically better response," Dr. Milne says. "I began to realize that if I compressed on the cornea vigorously, the radiofrequency pulse was impeding its ability to shrink the collagen."

From this and subsequent clinical experience, as well as information from a colleague on the mechanics of collagen's response to heat a well as the inhibitory effect of pressure on the contractile component of corneal collagen, he developed the LightTouch technique for CK. "With LightTouch, we use fewer spots further out to get more reaction," he says.

Dr. Milne says there are three main components of the LightTouch technique:

■ Keep the corneal surface dry. Drying out the cornea allows for visibility during the procedure. Excess fluid on the surface of the cornea can hinder the surgeon's ability to see the contracting material, hindering consistency in treatment.

■ Use equal pressure. Dr. Milne recommends a 2-mm dimple around the probe tip at the beginning of the pulse to generate mild to moderate pressure evenly.

■ Follow down posteriorly through the pulse. This is a crucial step, he says, because the cornea contracts so vigorously in response to the radiofrequency energy that it can pull away from the CK probe tip, producing a shallow effect at the end of the pulse.

Clinical results

Dr. Milne says that he has performed CK on over 2,000 eyes and since employing the LightTouch technique, 95% of his patients are within 0.5 D of the preop goal. Even more impressive is the line-for-line variable between near vision gained vs. distance vision lost.

"The thing that's really interesting about CK is that on average, for every seven lines of near vision that patients gain, only one line of distance vision is lost," says Dr. Milne. "There's nothing else out that that can produce these results. Everything else is 1 line for 1 line, be it lens or laser."

Regression is an issue, but Dr. Milne says that it is no different from a hyperopic laser treatment. "The regression or stability of CK is actually similar to that of the laser for hyperopic treatment and there have been some studies that demonstrate this. Patients will need retreatment as their presbyopia progresses, but it's no different than if they received laser correction for hyperopia," he says. "Both procedures have about a 0.03 D loss per line after 6 months and they both lose about 18-25% of their effect 6 months postop."

Dr. Milne says that CK is a perfect entry-level procedure for patients with emmetropic presbyopia. "These patients are not going to get bilateral implants and pay $8,000, and they don't want laser because the laser is going to give them true monovision where they lose line for line," he says. "This is the safest procedure that makes the most sense for them."