Conductive keratoplasty for hyperopia offers impressive stability and safety

Hyperopic outcomes comparable to LASIK in low myopia, data from phase 3 study indicate.

STANFORD, Calif. — Conductive keratoplasty for the treatment of hyperopia provides excellent stability and safety, according to a phase 3 study. Outcomes are comparable to LASIK and the visual axis is spared.

“Conductive keratoplasty (CK) uses the cornea’s conductive properties to induce a permanent collagen shrinkage,” said investigator Edward E. Manche, MD, an assistant professor of ophthalmology and director of cornea and refractive surgery at Stanford University School of Medicine here. “CK is somewhat different than traditional laser thermal keratoplasty in that it creates a cylindrical footprint as opposed to a conical footprint.”

CK, which uses the ViewPoint CK system (Refractec Inc., Irvine, Calif.), is currently being evaluated for low to moderate hyperopia. “Treatments for compound hyperopic astigmatism and consecutive hyperopia are also being studied,” said Dr. Manche.

He said he appreciates the fact that the ViewPoint system is compact. “It is about the size of a VCR or DVD player. It only weighs about 15 pounds,” he said. “I simply place it on top of one of my excimer lasers when I’m using it for the trial.”

Radio frequency energy

CK employs a 450-µm probe inserted into the cornea. Radio frequency energy is delivered via a foot pedal. The energy level is preset for 0.6 second.

The simple surgical procedure consists of applying topical anesthesia, inserting a lid speculum, marking the eye and applying treatment. “The total time is less than 5 minutes. The cornea tightens, which results in steepening,” Dr. Manche said.

Dr. Manche shared results of a phase 3 clinical study at the American Academy of Ophthalmology meeting in Dallas. A total of 400 patients were enrolled. (Fifty of these were treated in stage 1, in which the nomogram was refined.) The range of treatment was +1 D to +4 D of spherical hyperopia, with less than 1 D of cylinder. Subjects had no prior refractive surgery or significant ocular or physical history.

Average patient age was 55 (range 40 to 74) and the average spherical equivalent was +1.8 D (range +0.75 D to +3.75 D). Uncorrected visual acuity at distance was 20/40 or worse in 81% of patients. Reading acuity was J 5 or worse in 92% of eyes treated. Patients were followed for a minimum of 24 months.

After treating the first 50 eyes, the investigators elected to no longer treat patients above +3 D because the current nomogram was undercorrecting patients.

Faint leukomas

Once energy is delivered to the eye via a foot pedal, small, white leukomas appear over the area of treatment. “These leukomas are much more faint than what is observed with laser thermal keratoplasty (LTK),” Dr. Manche said. “With LTK, the leukomas look much whiter and there is more of a snowball effect.”

Slit-lamp photography 1 hour after CK also revealed small leukomas. “Again, they tend to be very faint,” Dr. Manche said. Striae radiate between the leukomas. “This is one of the few instances that you’re happy to see striae,” he said.

Preoperative topography shows a spherical cornea. At 1 hour postop, “you can see this is a 24-spot treatment,” Dr. Manche said. At 1 week, a relatively normal central cornea is achieved. Finally, at 6 months, “the cornea is quite regular centrally,” he said. “You’ve induced about 3.5 D of steepening centrally.”

Visual acuity results indicated 96% of eyes were 20/40 or better at 6 months, and 78% of eyes were within 1 D of intended correction. “At 12 months, you have similar results, with 92% of eyes 20/40 or better, and 92% of eyes within 1 D of the attempted correction,” Dr. Manche said. No eyes were retreated.

Stable procedure

There was a five-line improvement in mean uncorrected near vision. “Stability was achieved at approximately 6 months. There was also no statistically significant change in stability between months 6 and 12,” Dr. Manche said.

The change between 3 and 6 months was 0.25 D. “But between months 6 and 9 you have 0.09 D of shift, and between 9 and 12 months, 0.09 D of shift. That’s only a 0.18 D shift over a 6-month period,” he said.

The safety of CK was also superb, according to Dr. Manche. No eyes lost lines of BCVA at 1 year and no eyes had an increase of cylinder greater than 2 D. No eyes were worse than 20/40. “CK has an outstanding safety profile,” Dr. Manche said. A large optical zone is created, “so these patients are not affected much by visual aberrations, such as nighttime haloes,” he said.

The procedure “is safe enough that the Food and Drug Administration allowed us to proceed with bilateral, simultaneous treatments after our pilot study of 50 eyes to refine our nomograms,” Dr. Manche said.

For Your Information:

• Edward E. Manche, MD, can be reached at 900 Blake Wilbur Dr., Rm. W3002, Palo Alto, CA 94304; (650) 725-5765; fax (650) 498-6488; e-mail: mu.edm@forsythe.stanford.edu. Dr. Manche has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

• Refractec Inc., manufacturers of the ViewPoint CK system, can be reached at 3 Jenner, Ste. 140, Irvine, CA 92618; (949) 784-2600; fax: (949) 784-2601.