Conductive keratoplasty, or CK, is a procedure that utilizes radio frequency waves to shrink collagen for the correction of hyperopia or astigmatism. Here’s a look at how the surgeon performs this procedure and at some of the documented results.
The Surgeon’s Work
The procedure starts when the surgeon places the 450-micron tip on the peripheral cornea that he or she has already marked with a corneal marker. Once in place, the tip releases controlled radio-frequency energy, cooling the stromal collagen to 65C. This, in turn, shrinks the surrounding tissue and creates a cylindrical footprint that is consistent from point to point along the circular treatment zone.
In all, the surgeon places eight treatment spots along the periphery of the cornea at a diameter of 6mm, 7mm or 8mm—or in a combination of all three, depending on the correction needed. Similar to the purse string analogy, this band of tightening causes the central cornea to steepen. Investigational studies indicate this procedure can correct up to 3.00D of hyperopia.
The Results So Far
Ophthalmologists Penny Asbell and Robert Maloney performed one study to determine if CK maintained stability of the refractive correction of hyperopia.1 In 162 eyes with preoperative hyperopia of +0.75D to +3.00D, they found 20/40 vision in 93% of patients, and only small changes in residual refractive error appear after CK. This suggests that refractive error stabilizes at six months. In fact at 6–9 months the change was only 0.14D, and from nine to 12 months only 0.08D.
In terms of safety, a paper John Davidorf, M.D., and Peter Hersh, M.D., presented at the American Society for Cataract and Refractive Surgery looked at the effects of CK on the corneal endothelium. It showed no statistical effect when comparing endothelial cell counts from pre-op with three, six and 12 months post-op.2 In another study, Dr. Hersh showed that 77% of treated eyes were within 0.50D of target, and 97% were within 1.00D six months after CK.3
CK technology has many advantages. It is a small, portable unit that will likely be far less expensive than other collagen-shrinkage technologies. It enables the surgeon to place the probe in any specific place on the cornea. This may make CK a preferred procedure for correcting astigmatism.
CK may be the technology that replaces incisional enhancement procedures, such as astigmatic keratectomy or limbal relaxing incisions. If a patient has any residual astigmatism after LASIK or cataract surgery, doctors may one day use CK at the slit lamp to treat astigmatism without weakening the eye the way incisional enhancement does.
Refractec Inc. of Irvine, Calif., manufactures the CK technology. It has completed phase III data and recently filed for FDA approval.
Dr. Karpecki is medical director for cataract, refractive surgery and anterior segment disease and Hunkeler Eye Centers, a NovaMed EyeCare Management practice, in Overland Park, Kan.
1. Maloney RK, McDonald MB. Davidorf JM, Hersh PS, Manche EE, Lindstrom RL, Asbell PA, Brint S, Culbertson W, Durrie DS, Grene RB, Sugar A. Interim results of 400 eyes enrolled In the U.S. Clinical Trial of Conductive Keratoplasty for the Correction of Hyperopia. ASCRS abstract, 2001.
2. McDonald MB, Davidorf JM, Hersh PS, Maloney RK, Manche EE. 12-month results from the U.S. Clinical Trial of Conductive Keratoplasty for the Correction of Hyperopia. ASCRS abstract, 2001.
3. Hersh PS. Personal experience with conductive keratoplasty. ASCRS abstract, 2001.
