Safety and efficacy of bilateral topical application of rocuronium bromide for mydriasis in European kestrels (Falco tinnunculus).

The avian iris is mainly composed of striated muscle fibers, and the topical parasympatholytic drugs used in mammals to induce pupil dilation are ineffective in birds. The achievement of mydriasis in conscious birds is only possible by using neuromuscular blocking agents such as curariform drugs. To determine the efficacy of the neuromuscular blocking agent rocuronium bromide as a mydriatic agent in European kestrels (Falco tinnunculus) and to assess possible adverse effects due to its use, 10 kestrels received a single topical instillation with a pipette of 0.12 mg of rocuronium in each eye (total dose, 0.24 mg/bird). Pupil diameter was measured with a pupillary gauge, and pupillary light reflex was assessed by using a standard light source from time zero (Tbase) to 250 minutes after application (T250). Baseline pupil size (Tbase) was 3.30 (0.71) mm in both eyes. Maximal mydriasis was achieved at T90 minutes with a mean (SD) pupillary diameter of 6.30 (0.42) mm and 6.35 (0.41) mm in the right eye and left eye, respectively. At the dose used, rocuronium bromide induced a consistent bilateral simultaneous mydriasis without noticeable adverse effects, and it can be considered a reliable and safe topical mydriatic agent in kestrels.