Long-term results of excimer phototherapeutic keratectomy (PTK) for corneal scars and dystrophies

Purpose. To assess the long-term effect of the subtotal (9-10 mm) ablation of Bowman's membrane in a PTK strategy designed to avoid postoperative hyperopic shift. Methods. In 87 eyes with various types of corneal scars and dystrophies, a 9-10 mm ablation zone (AZ) (Nidek EC 5000) was used in conjunction with low-molecular 0.4% hyaluronic acid masking fluid to create an even postoperative surface. This technique has previously been shown to sharply decrease postoperative hyperopic shift. Best corrected visual acuity (BCVA), manifest refraction, and corneal topography were used to evaluate the outcome. Minimum follow-up time was one year. Results. At 12 months postoperatively, mean BCVA increased by 2.1 ± 0.32 Snellen lines. There was no loss of BCVA in any eye. The mean change in refraction was +1.15 ± 3.98 D, for an average of 93 μ of ablated corneal tissue. Videokeratography showed stability of topography after the initial 6 postoperative months, as well as a dioptric range of only 3-4 D within the central 4.0 mm. Corneal transparency increased in all eyes. There were no wound healing problems despite the large ablation zone. Conclusions. Altering traditional PTK technique, by substantially increasing the AZ diameter and using a special masking fluid, improves refractive results (by markedly decreasing post-operative hyperopia) without adverse effects such as ektasia, late development of dense haze or instability of refraction.