Increased higher-order optical aberrations after laser refractive surgery: a problem of subclinical decentration.

PURPOSE: To study the clinical and theoretical effects of subclinical decentrations on the optical performance of the eye after photorefractive laser surgery.

SETTING: Department of Ophthalmology, University of Dresden, Dresden, Germany.

METHODS: Ocular aberrations were determined before and 1 month after uneventful photorefractive keratectomy (PRK) with the Multiscan laser (Schwind) in 10 eyes of 8 patients. The corrections ranged from -2.5 to -6.0 diopters, and ablation zones of 6.0 mm and larger were used. The measured wavefront errors were compared to numerical simulations using the individually determined decentrations and currently used ablation profiles.

RESULTS: The PRK-induced aberrations were significantly greater than the preoperative aberrations. The numerically calculated increase in the higher-order optical aberrations correlated with the clinical results, demonstrating a major increase in coma- and spherical-like aberrations. Subclinical decentration (less than 1.0 mm) was found to be a major factor in increased coma-like and spherical-like aberrations after corneal laser surgery.

CONCLUSION: To minimize higher-order optical errors, special efforts to center the ablation zone are necessary; for example, by eye-tracking systems that consider the visual axis.