Enlargement of the photorefractive keratectomy optical zone

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Abstract
Purpose: To evaluate the safety and efficacy of a photorefractive keratectomy (PRK) re-treatment procedure that enlarges the optical zone and treats undercorrection. Setting: Rotterdam Eye Hospital and Medisch Centrum Alkmaar, The Netherlands. Methods: This study evaluated 16 eyes that had PRK for myopia with the Summit excimer laser that resulted in a mean undercorrection of −2.82 diopters (D). Patients also reported impaired night vision including difficulty in driving, halos, and stray light and ghost images. These phenomena persisted after spectacle correction of residual refractive error, necessitating further treatment with a larger ablation zone. With a VISX 20/20 excimer laser, the optical zone was enlarged to 6.0 mm and undercorrection treated with a 6.0 mm ablation. Results: At 13.5 months after re-treatment, mean reduction in myopia was 1.70 D, resulting in a residual undercorrection of −1.08 D. In seven eyes, final refraction was within 1.00 D of emmetropia. Only two patients continued to report nightdriving problems. Conclusions: Re-treating undercorrections combined with enlarging the ablation zone resulted in a reduction in myopia from a mean of 2.82 to 1.08 D. Subjective reports of halos and stray light images were decreased in all cases.