Hyperopic thermokeratoplasty: clinical evaluation

A new procedure, hyperopic thermokeratoplasty (HTK), developed in the Soviet Union for the correction of hyperopia, uses controlled thermal burns of the corneal stroma with a retractable probe tip preset to penetrate the cornea at 95% depth. The coagulations are applied in a radial pattern for spherical hyperopia. Only the peripheral cornea is treated and the effect is titrated by varying the optical zone and number of rays. The thermal effect flattens the peripheral cornea and steepens the central cornea. In this report, we prospectively evaluated the refractive results of a group of 61 HTK patients. Mean preoperative spherical equivalent was 3.9 diopters (D). Mean follow-up to date is 5.2 months, with 44% of cases evaluated at six months and 31% at one year. The initial effect of surgery (at one day) was a mean decrease in hyperopia of 6.0 D (standard error of the mean [S.E.] = 0.3 D), resulting in a mean spherical equivalent of -2.1 D (S.E. = 0.2 D). There was a steep regression of effect between one day and two months at which point average refraction was close to emmetropia. After two months, there was a gradual but continuing regression of effect, leveling off after six months. At five to six months, 63% of cases were undercorrected by at least a diopter; at 9 to 12 months, 83% of cases were undercorrected. The overall change in spherical equivalent at each time increased as optical zone size decreased.(ABSTRACT TRUNCATED AT 250 WORDS)