[Anisocoria after unilateral photorefractive keratectomy. Result of a lesion of the pupillary sphincter muscle?]. / Anisokorie nach einseitiger photorefraktiver Keratektomie. Ausdruck einer Läsion des Pupillensphinktermuskels?

BACKGROUND: After unilateral photorefractive keratectomy (PRK) for myopia correction, relative mydriasis of the treated eye was noticed. The aim of this study was to determine the incidence and possible etiology of this anisocoria. PATIENTS AND METHODS: In a prospective clinical study we examined eight consecutive patients after PRK of a spherical equivalent of -1.0 to -8.5 D with a 6.5-7.0 mm optical zone (Schwind-Keratom) for up to 10 months. Measurements of the pharmacological uninfluenced pupillary diameter were carried out with a Goldmann perimeter under 31.5 asb and under four different room light and distance conditions. In five patients a hard contact lens of 0 D power was fitted to the treated eye, so that the laser-induced central corneal flattening was compensated for by the sublenticular tear film, and the pupillary diameter was measured again. The influence of pilocarpine 0.1% eye drops to the pupil was also examined. RESULTS: Postoperatively, the pupil of the PRK-treated eye measured up to 1.75 mm larger than that of the fellow eye in all patients. The amount of anisocoria showed a small negative correlation with the interval between the PRK procedure and the day of measurement. It did not correlate significantly with the amount of induced refractive change, applied energy, application of pilocarpine 0.1% eye drops or the contact lens fitting. CONCLUSION: After unilateral PRK, anisocoria can regularly be observed. At present its definite pathogenesis is unclear, although certain possible optical and neuronal mechanisms have been excluded. The most probable etiology is a mild lesion of the pupillary sphincter muscle because of its localization in the center of the laser shock wave distribution.