Pupillary responses and blink reflex in myotonic dystrophy.

We have studied pupillary responses to parasympathetic and sympathomimetic agents, pupillary cycle time and the electrophysiology of the blink reflex in 18 patients with myotonic dystrophy. The response of the iris to dilute pilocarpine and phenylephrine did not indicate pharmacologic supersensitivity. Pupillary cycle time was prolonged in nine of the 18 patients. Ipsilateral R1 blink reflex latencies were normal in all cases, and bilateral R2 were normal in 16 of the 18 patients. These results do not support either autonomic or brainstem dysfunction in the majority of patients with myotonic dystrophy. In 50% of the patients the results are compatible with smooth muscle involvement of the iris.