Relative mydriasis after photorefractive keratectomy

PURPOSE: To report the incidence of anisocoria after unilateral excimer laser photorefractive keratectomy (PRK) for myopia and subsequent corticosteroid therapy in a retrospective and prospective study and to explore possible etiologies. METHODS: The horizontal pupil diameter was determined in 6 patients (6 eyes) at 21.8 12.6 months after unilateral wide- field excimer laser PRK (retrospective group) as well as in 8 consecutive patients (8 eyes) before and 3.4 ± 2.9 months after unilateral PRK (prospective group). The Sehwind-Keratom wide-field excimer laser was used. Measurements were done in an examination room using Rosenbaum card comparison pupillometry and with a Goldmann perimeter at 31.5 asb. In the prospective group, the effect of fitting a hard contact lens of zero diopter power and the application of 0.1% pilocarpine were evaluated. RESULTS: Relative mydriasis was present in all treated eyes and the difference in pupil diameter between the two eyes measured 0.25 to 1.75 mm (retrospective group: +0.56 ± 0.82 mm; prospective group: +0.72 ± 0.29 mm). At the time of pupil measurement, the retrospective group had a significantly longer mean postoperative follow-up (21 mo) than the prospective group (3.4 mo) and significantly more eyes still received topical corticosteroid treatment (retrospective group, 1 of 6 eyes; prospective group, 7 of 8 eyes). The amount of anisocoria did not correlate with the applied laser energy, ablation depth, or refractive change, but showed a negative correlation with increasing time after PRK. Neither hard contact lens fitting nor pilocarpine 0.1% reduced the amount of anisocoria significantly. CONCLUSION: Unilateral PRK with wide-field excimer laser ablation and subsequent application of topical corticosteroids regularly resulted in a relative pupillary mydriasis. Neither an altered corneal profile nor parasympathetic denervation is responsible for this. Weakening of the pupillary sphincter of the treated eye may cause this phenomenon.