Refractive changes after excimer laser phototherapeutic keratectomy

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Abstract
Purpose: To study the visual and refractive changes in patients with superficial corneal opacities after excimer laser phototherapeutic keratectomy (PTK). Setting: Eye Clinic, Kobe Kaisei Hospital, Kobe, Japan. Methods: One hundred twelve eyes of 80 patients with superficial corneal opacities had PTK with the Nidek EC-5000 excimer laser system. All patients had routine ophthalmic examinations including uncorrected and Landolt best corrected visual acuity (BCVA) measurements, subjective and objective refractions, keratometry, EyeSys (Premier Laser Systems, Inc.) corneal topography performed before and 1 week and 1, 3, 6, and 12 months after PTK, and pachymetry performed before and 12 months after PTK. The change in refractive status within 12 months of PTK and the relationship between factors such as ablation depth, transition zone (TZ) setting, and use of masking agents and the amount of hyperopic shift were also assessed. Results: The BCVA increased by more than 2 lines in 65.1% of eyes and by 1 line in 24.1%. The BCVA did not change in 12 eyes (10.8%) because of cataract or underlying retinal disease. A mean hyperopic shift of 3.42 ± 1.15 diopters (D) (range 1.00 to 5.25 D) was seen in all eyes at 12 months. The hyperopic shift peaked 1 month after PTK and tended to decline after that; it stabilized at 12 months. Conclusion: Although PTK is a safe and efficient method for the treatment of superficial corneal opacities, induced hyperopia after the procedure remains a major problem. A shallow ablation depth (less than 100 μm), presence of a TZ setting, and use of a masking agent decrease the hyperopic shift significantly.