Refractive surgery with the ArF excimer laser (photorefractive keratectomy) : surgical technique, wound healing and refractive results

Excimer lasers have been adapted to treat refractive errors in the human eye since 1987. By remodeling the corneal surface, myopia and astigmatism can be corrected. The investigations herein were performed during a time period when the surgical technique development was extensive. It was necessary during this time to evaluate the outcomes in order to document improvement in the refractive results and the quality of vision.The visual outcome and the wound-healing performance are very closely related in this type of surgery.

This study deals with the refractive outcomes of the photorefractive keratectomies (PRK) of different laser models as well as factors that influence these results. Refraction, uncorrected visual acuity, contrast sensitivity, and centration were evaluated. The different components in corneal wound healing and its dependence onlaser beam characteristics and beam delivery systems were evaluated clinically and experimentally. Histochemistry, pachometry, and planimetry were used. With the exception of laser algorithms causing slight myopia in one system and the beneficial effects of increasing the beam diameter, no differences were found between the laser brands. Variations in beam delivery systems in order to smooth the treated corneal surface profile were studied with special reference to the influence of involuntary eye movements. The refractive results of PRK in almost all treated patients were good. In patients that did not achieve the expected refraction a reoperation gave, in most cases, acceptable results so that a total of 97% of all treated and eventually retreated patients had an uncorrected visual acuity of 0.5 or better.

In conclusion, our investigations show that the choice between the two most used iris aperture lasers is not significant to the refractive results in treatments with the larger diameter of 6 mm. A large ablation diameter is important in order to avoid halo effects and night vision problems. The refractive results in general were good, stable, and predictable. Comparisons between the epithelial thicknesses showed no differences in patients whose one eye had been treated with Summit laser and the other with VISX laser. The two lasers showed no difference when the epithelial healing phase was compared in an experimental study. Increasing the number of times a shutter is opened in a treatment does not result in a smoother wound surface, since the natural movements of the eye contribute to create a smooth surface. Epithelial hyperplasia and/or excessive extracellular matrix formations, such as hyaluronan, contributes to haze formation and regression. Haze disappears with time and regression can be reoperated with good results.