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

Sammanfattning: Excimer lasers have been adapted to treat refractive errors in the human eye since1987. By remodeling the corneal surface, myopia and astigmatism can be corrected.The investigations herein were performed during a time period when the surgical techniquedevelopment was extensive. It was necessary during this time to evaluate the outcomesin 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 inthis 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 wereevaluated. The different components in corneal wound healing and its dependence onlaser beam characteristics and beam delivery systems were evaluated clinically andexperimentally. Histochemistry, pachometry, and planimetry were used. With the exception of laseralgorithms causing slight myopia in one system and the beneficial effects of increasingthe beam diameter, no differences were found between the laser brands. Variationsin beam delivery systems in order to smooth the treated corneal surface profile werestudied with special reference to the influence of involuntary eye movements. Therefractive results of PRK in almost all treated patients were good. In patients thatdid not achieve the expected refraction a reoperation gave, in most cases, acceptableresults so that a total of 97% of all treated and eventually retreated patients hadan uncorrected visual acuity of 0.5 or better. In conclusion, our investigations show that the choice between the two most usediris aperture lasers is not significant to the refractive results in treatments withthe larger diameter of 6 mm. A large ablation diameter is important in order to avoidhalo effects and night vision problems. The refractive results in general were good,stable, and predictable. Comparisons between the epithelial thicknesses showed nodifferences in patients whose one eye had been treated with Summit laser and theother with VISX laser. The two lasers showed no difference when the epithelial healingphase was compared in an experimental study. Increasing the number of times a shutteris opened in a treatment does not result in a smoother wound surface, since the naturalmovements of the eye contribute to create a smooth surface. Epithelial hyperplasiaand/or excessive extracellular matrix formations, such as hyaluronan, contributesto haze formation and regression. Haze disappears with time and regression can bereoperated with good results. Key words: Photorefractive keratectomy, excimer laser, comparison, centration,contrast sensitivity, night vision, endothelial cell, epithelial thickness, multipass/multizone,multizone, haze, saccades, hyaluronan, myopic regression, reoperation, wound healing. ISBN 91-628-2631-X