Abstract
Abstract: :
Purpose: To use numerical models to predict diopter changes in the cornea resulting from application of radiofrequency (RF) current and to treat pig eyes to determine variability in resistance and power delivery. Methods:: RF current is being used to shrink corneal collagen at peripheral points to produce a given amount of corneal steepening, measured in diopters, in a procedure called conductive keratoplasty (CK). In CK, a monopolar electrode is inserted into the cornea to deliver pulsed RF current. We developed mathematical models of electric and current density fields, thermal fields, and the resulting tissue damage to predict and quantify corneal shrinkage in the CK process. We used the finite difference method to obtain results from the models. CK treatments on pig eyes were evaluated for variability in resistance and power delivery. Results: Initial tissue shrinkage occurred at the tip of the electrode and gradually moved up the electrode shaft. Changes in tissue properties during RF activation result mostly from heating processes in tissue water. A change of 10% in applied power may result in 60% variation in refractive effects. Boundaries of collagen birefringence loss compared favorably with histology of CK treated tissue. Treatment of pig eyes showed up to 62% min–max variability in corneal resistance curves, depending upon the technique used to apply the energy. Actual CK power delivered to the cornea varied between 6.2% and 32.1% with respect to nominal values, indicating potentially large, technique–dependent fluctuations in the amount of corneal collagen shrinkage. Conclusions: Diopter value correlated linearly with % circumferential shrinkage of cornea. The numerical models produced reasonable and useful predictions of corneal shrinkage through CK. Surgeon factors may account for some of the outcome variability based upon technique–dependent alterations in the resistance curves during energy delivery.
Keywords: cornea: basic science • refraction