Anisocoria after unilateral photorefractive keratectomy - expression of a lesion of the pupillary sphincter muscle?

Background: After unilateral photorefractive keratectomy (PRK) for myopia c orrection, relative mydriasis of the treated eye was noticed. The aim of th is study was to determine the incidence and possible etiology of this aniso coria. Patients and methods: In a prospective clinical study we examined eight con secutive patients after PRK of a spherical equivalent of -1.0 to -8.5 D wit h a 6.5-7.0 mm optical zone (Schwind-Keratom) for up to 10 months. Measurem ents of the pharmacological uninfluenced pupillary diameter were carried ou t with a Goldmann perimeter under 31.5 asb and under four different room li ght and distance conditions. In five patients a hard contact lens of 0 D po wer was fitted to the treated eye, so that the laser-induced central cornea l flattening was compensated for by the sublenticular tear film, and the pu pillary 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 an isocoria showed a small negative correlation with the interval between the PRK procedure and the day of measurement. It did not correlate significantl y with the a mount of induced refractive change, applied energy, applicatio n 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 opt ical and neuronal mechanisms have been excluded. The most probable etiology is a mild lesion of the pupillary sphincter muscle because of its localiza tion in the center of the laser shock wave distribution.