Conductive keratoplasty likened to LASIK in phase 3 study

Radio-frequency collagen shrinkage procedure offers predictability and spares the visual axis.

NEW YORK — Conductive keratoplasty (CK) provides outcomes similar to LASIK in the treatment of low to moderate hyperopia, according to a report on 1-year outcomes of a multicenter, phase 3 clinical trial of Refractec’s ViewPoint CK System.

“We have excellent safety with no loss of best corrected visual acuity (BCVA) at the 1-year mark. The outcomes are comparable to LASIK, and the visual axis is spared,” said Edward E. Manche, MD, here at the Ninth Annual Ocular Surgery News Symposium.

The ViewPoint system is about the size of a VCR and weighs about 10 to 15 pounds. It is foot-pedal driven, and radio-frequency energy is delivered into the cornea via a hand piece tipped with an insulated probe.

“Conductive keratoplasty uses the cornea’s conductive properties to induce a permanent collagen shrinkage,” Dr. Manche said. “The tip, which is 450 µm, is inserted in the cornea and the energy is applied at eight meridians.” A variable number of spots are applied depending upon the degree of hyperopia, he reported.

Uniform shrinkage

The radio-frequency energy heats the corneal tissue to a uniform 65° C, resulting in a uniform shrinkage of the corneal collagen tissue and a steepening of the central cornea. The procedure is simple to perform, Dr. Manche said. “You instill some topical anesthesia and insert an insulated lid speculum,” he said. “Then you mark the eye with eight meridians using a special marker and apply the treatment. The entire procedure takes less than 5 minutes. Depending on the number of spots, it can be done in about a minute.”

Easily installed

---Central corneal steepening as a result of CK treatment application is shown.

The treatment nomogram indicates that a spot is applied on the cornea for 0.6 second at 6 mm, 7 mm and 8 mm. The procedure can be performed under a microscope or at the slip lamp. “The beauty of the system is that it can be easily installed into most offices, and it’s a very quick and easy procedure,” said Dr. Manche.

Dr. Manche compared CK to laser thermal keratoplasty (LTK). “The question is whether or not CK is going to be more stable than LTK,” he said. With CK the temperature is consistent, compared to a gradient temperature with LTK. The depth of treatment is approximately 75% to 80% with CK and 50% with LTK. To get more treatment effect with CK, the surgeon increases the number of rings; with LTK, the surgeon increases the energy or temperature to increase the treatment effect. Predictability is considered good with CK, according to Dr. Manche. “With CK, we are seeing stability at about 3 to 6 months with pretty good predictability,” he said.

Study outcomes

---Corneal marker provides physicians with a template for CK treatment application.

Dr. Manche reported on 54 patients ranging in age from 40 to 74. The study participants had 1 D to 4 D of spherical hyperopia, no more than 1 D of cylinder and no prior refractive surgery. The average spherical equivalent was 1.8 D, ranging from +0.75 D to +3.75 D. “The (preop) distance acuities were worse than 20/40 in 81% and near worse than J 5 in 92%,” Dr. Manche reported.

One hour postoperatively small white leukomas are visible at the site of the treatment spots. Striae are also visible. “This is probably one of the only times you will want to see striae,” said Dr. Manche.

Six months postop, 96% of patients were at 20/40, with 78% within 1 D, and 61% were 20/20 with 57% within 0.5 D. One year postop, the outcomes are slightly better with 92% and 62% at 20/40 and 20/20 respectively, and 92% and 54% within 1D and 0.5 D, Dr. Manche said. “They achieve stability at 6 months with no statistically significant change between months 6 and 12,” he said. Between 3 and 6 months postop there was a change of 0.26 D, while the change between 6 and 9 months and between 9 and 12 months was insignificant.

Safety variables are excellent, Dr. Manche reported. No patient lost two lines of BCVA, was worse than 20/40 a year after surgery or had greater than a 2 D increase in cylinder 1 year postoperatively. “We obviously need longer-term follow-up to assess the stability, but at this point in time it’s very encouraging,” said Dr. Manche.

Treatments using CK for compound hyperopic astigmatism and consecutive hyperopia following previous refractive surgical procedures are being investigated.

---Controlled release of radio frequency energy heats stromal tissue to a precise 65° C.

For Your Information:

• Edward E. Manche, MD, can be reached at 300 Pasteur Dr., Room A-157, Stanford, CA 94305; (650) 723-5517; fax: (650) 723-7918. Dr. Manche has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.