Does hyperopic radiofrequency mirror hyperopic PRK/LASIK?

Although different from thermokeratoplasty, radiofrequency for hyperopia has vision results comparable with hyperopic refractive surgery.

Issue: June 1, 2000

The goal of hyperopic radiofrequency or conductive keratoplasty (CK) is to reduce the dependency of those with hyperopia on glasses and contact lenses. The technique utilizes Refractec Inc.’s (Irvine, Calif.) Viewpoint CK System, which is in phase 3 clinical trials and recently received Food and Drug Administration approval to begin simultaneous bilateral treatment in clinical trials. The recent approval came in response to the company’s solid safety and stability data, according to Refractec.

At the New Orleans Academy of Ophthalmology meeting, Robert K. Maloney, MD, from the Maloney Vision Institute, presented phase 3 results. The study data demonstrated a minor postoperative regression in vision of 0.38 D between 1 and 3 months, with 0.125 D regression between 3 and 6 months. Additionally, a majority of patients achieved 20/40 or better visual acuity.

How it works

---The Viewpoint CK System consists of a probe with a 450 µm long, 90 µm wide needle-like tip. This is placed into the cornea and a foot switch is hit, sending energy into the cornea. This results in a very small-diameter full-thickness corneal lesion.

Also referred to as a radiofrequency keratoplasty, CK is a minimally invasive, non-laser approach for vision correction, which utilizes a high-frequency low-power energy source to deliver electrical energy uniformly throughout the thickness of the cornea. Thermal spots are positioned in a ring formation at a 6, 7 or 8 mm optical zone. The treatment spots help to reshape the tissue. This steepens the cornea’s optical surface to better focus light and treat farsightedness.

“The spots are like a belt tightening around the cornea,” Dr. Maloney said. “You heat the cornea, collagen shrinks, tightens like a belt and that corrects hyperopia by steepening the cornea.”

The numbers of rings of spots that are placed on the cornea control the amount of correction that is achieved. This procedure does not result in any damage to the surrounding tissue. This is due to the fact that it is not dependent on thermal conductivity. Instead, CK relies on the natural conductive properties of the cornea.

Although frequently compared with Fyodorov’s hot needle where a needle was heated and poked into the cornea in an effort to heat the cornea centrally, it is significantly different. The problem with these prior procedures was that as the needle passed through the cornea, it cooled off. Therefore, the heating was on the surface and the deep cornea was not treated, so the effect wore off. Holmium laser thermokeratoplasty also preferentially heats the superficial cornea, leading to regression of effect.

“What is different about CK is that it uses a probe that goes into the cornea while it’s cool and then radiofrequency energy is put through the probe,” Dr. Maloney said. “This creates uniform shrinkage in the deep cornea.”

The Viewpoint CK System consists of a probe with a 450 µm long, 90 µm wide needle-like tip. This is placed into the cornea and a foot switch is hit, sending energy into the cornea. This results in a very small-diameter full-thickness corneal lesion. The entire procedure takes about 1.5 minutes, according to Dr. Maloney.

Clinical outcomes

In the phase 3 clinical trials, 50 eyes of 50 subjects were included, which had 1 D to 4 D of hyperopia with less than 1 D of cylinder and a spherical equivalent of 1.9 D. After undergoing CK, at 3 months, 50% of patients were within 0.5 D of emmetropia and 85% were within 1 D of emmetropia. These results are comparable with the results of hyperopic laser in situ keratomileusis (LASIK), Dr. Maloney said.

Uncorrected distance vision also was comparable to hyperopic LASIK, with 90% of patients achieving 20/40 or better. Just less than 50% of patients obtained 20/20 vision. “We had undercorrections in our initial series, on average,” Dr. Maloney said. “That is why the visual acuity results weren’t quite as good.”

What about stability?

A regression of 0.38 D was observed between 1 month and 3 months. Additionally, there was 0.125 D of regression between 3 and 6 months. These results demonstrate that conductive keratoplasty is more stable than hyperopic photorefractive keratectomy (PRK), according to Dr. Maloney. In the hyperopic PRK trials for the Visx (Santa Clara, Calif.) Star S2, “there was 0.4 D regression between 1 and 3 months and 0.3 D of regression between 3 and 6 months,” Dr. Maloney said. “In other words, so far, CK is more stable than hyperopic PRK.”

Only one eye lost two lines of vision and one patient had an increase in cylinder of more than 2 D. This cylinder has since resolved and, subsequently, the best spectacle corrected visual acuity is back to baseline. According to Dr. Maloney, induced cylinder can occur with this procedure due to the intentional contraction of the cornea that is being caused. As with most refractive procedures, if the physician is not careful in the placement of the treatment, some cylinder can be induced.

For Your Information:

Robert K. Maloney, MD, can be reached at 10921 Wilshire Blvd., Ste. 900, Los Angeles, CA 90024; (310) 208-3973; fax: (310) 208-0169. Dr. Maloney has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

Refractec Inc. can be reached at 3 Jenner, St. 140, Irvine, CA 92618; (949) 784-2600; fax: (949) 784-2601.