治療的エキシマレーザー角膜表層切除術後の遠視化の原因について

Abstract

The postoperative hyperopic shift of the excimer laser phototherapeutic keratectomy (PTK) for treatment of corneal superficial opacitis in the major complication of this technique. To investigate the causes of this hyperopic shift, we ablated the PMMA plates, hard contact lenses and the corneas of white rabbits by excimer laser which was set to perform a therapeutic ablation. The hyperopic shift when the PMMA plates were ablated with a depth 50 μm was about 1 diopter, and the greater the numbers of pulses during ablation, the greater the tendency toward hyperopia. Regression analysis shows that the steeper the basecurve of the hard contact lenses, the greater the tendency toward hyperopia. The hyperopic shift in ablated rabbit corneas was about 3 diopters after 2 weeks, and it was continued to 3 months. There was a tendency that the greater the numbers of pulses during ablation and the steeper the curvature of the cornea, the greater hyperopic shift. The causes. of this hyperopic shift of the PTK were considerd to be the following : 1) the differential distribution of the energy density of the laser beam ; 2) the ablation rates between central and peripheral cornea are different ; 3) re-epithelizations in the peripheral area were thicker than those in the central area.