Problems of refraction after photorefractive keratectomy

Excimer laser photorefractive keratectomy (PRK) is a refractive procedure to correct myopia that is gaining worldwide acceptance. PRK has been performed as an open-ended clinical trial since January 1992, and specific problems have been encountered in refracting PRK patients.

A review of all cases of PRK performed with at least 1-year follow-up was conducted. Nine hundred and seventy-one eyes with myopia ranging from -2.00 to -15.00 diopters had preoperative manifest and cycloplegic refraction, and postoperative refraction at 3 months after treatment.

Refractive difficulty due to degradation of the retinoscopic reflex was encountered in patients who developed moderate to severe haze (seven eyes). Small ablation zones (5 mm) and decentered ablations also contributed to confusion in interpretation of the retinoscopic reflex. In addition, excessive accommodation, profound early myopic and hypermetropic shifts, postoperative irregular astigmatism and inaccurate autorefractometer readings contributed to difficulty in refraction.

Laser ablation of the central cornea produces alterations in optical homogeneity of the cornea that may cause significant refractive difficulties. Refracting PRK patients requires careful and consistent refraction by an experienced refractionist, both before and after laser treatment.