The long term refractive outcome of a photorefractive keratectomy (PRK) may depend on several factors such as age, intended correction, corneal hydration, and wound healing. Thus we introduce the effective ablation rate which includes both the corneal etching rate during the treatment and the healing process after the treatment. In this study we define the effective ablation rate as the etching rate calculated from the difference between intended correction and the achieved correction measured 6 months after PRK. We have evaluated our data to find correlation between the effective ablation rate and the age of treated patients and the intended myopic correction. We have performed photorefractive keratectomy by a Schwind Keratom 2F excimer laser. 613 eyes of 348 patients were treated. 311 cases were selected where the follow-up was at least 6 months long. The effective ablation rate was calculated for each case and we have found that the effective ablation rate of human cornea depended on not only the intended correction but also the age of patients. The effective ablation rate can be calculated by the following equation: κeff = 207 + 0.53A - 3.16Di, where A is the patient age in years, Di is the intended correction in diopters, and κeff is the effective ablation rate in nm/pulse. In the meaning of the above equation the effective ablation rate is increasing as the intended correction changing from low to high myopia (e.g., from -1 D to -9 D) or as the patient's age is increasing. Above 40 years age and in the case of the -6 D or higher intended correction the increased effective ablation rate very likely leads to hyperopic result, since the effective ablation rate is equal or higher than the nominal etching rate. To reach the best correction for all patients the observed dependence must be taken into account during design of PRK.
|Number of pages||4|
|Publication status||Published - Mar 1 2000|
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Condensed Matter Physics
- Industrial and Manufacturing Engineering