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CK helps near vision in presbyopic, post-surgical eyes
Conductive keratoplasty (CK) (NearVision, Refractec Inc.) improves near vision in presbyopic eyes and in presbyopic eyes that had undergone an excimer laser procedure.
Conductive keratoplasty (CK) (NearVision, Refractec Inc.) improves near vision in presbyopic eyes and in presbyopic eyes that had undergone an excimer laser procedure.
Two experts in the technique discuss how the procedure has been incorporated into their practices.
CK treatment to improve near vision involves inducing slight to moderate myopia, -1 to -1.5 D, in the patient's nondominant eye. Patients who have undergone the procedure show improved near vision without experiencing significant, compromised functional distance vision, as occurs with excimer laser monovision procedures, he explained.
CK works, Dr. Pascucci explained, like a belt tightening the cornea in the mid-periphery when a full circle of treatment spots is applied. The central cornea steepens, and the corneal asphericity increases. This happens because the resistance of the stromal tissue creates even heating along the path of the keratoplasty tip. When the corneal tissue is heated from the bottom to the top, there is deep stromal collagen contraction in the treatment spot. This produces a cylindrical footprint about 80% deep.
Nomogram adjustment Typically, when using the 16-spot nomogram, the treatment is applied at the 6- and 7-mm optical zones to achieve 1 to 1.625 D of correction. With the 24-spot nomogram, the spots are applied at the 6-, 7-, and 8-mm optical zones for 1.75 to 2.25 D of correction. When performing CK after LASIK, the nomogram must be modified because collagen shrinkage under this circumstance is quite robust. Usually an eight-spot treatment will suffice after LASIK.
Dr. Pascucci and Daniel S. Durrie, MD, conducted a study in which they evaluated whether CK can provide functional near vision in patients with presbyopia who had undergone LASIK, LASEK, or PRK. Forty-two patients (42 eyes) were treated with CK after undergoing LASIK, LASEK, or PRK and followed for 3 months. The mean patient age was 52 ± 4 years (range, 44 to 60).
Before CK, the mean sphere was 0.20 ± 0.49 D (range, 0.75 to -1.25 D), the mean cylinder was -0.23 ± 0.26 D (range, 0.0 to -0.75 D), and the mean spherical equivalent was -0.31 ± 0.50 D (range, -0.75 to -1.25 D). Thirty-eight patients had undergone LASIK, one underwent LASEK, and three underwent PRK. The patients underwent the procedures a mean of 48 ± 27 months before CK (range, 6 to 143). All eyes were treated with eight spots at a 7.5-mm optical zone. The mean corneal pachymetry value was 493 ± 103 µm (range, 226 to 651 µm). The near add before CK was 1.70 ± 0.68 D (range, 0.0 to 3.00).
Dr. Pascucci reported that the near vision values increased with time after CK.
