Sildenafil citrate was developed to treat angina, but was found to also inhibit PDE in the corpus callosum and is now widely used to treat impotence. We report a case of enlargement of the inferior rectus muscle after sildenafil citrate ingestion.

A 58-year-old male presented with binocular diplopia which started 2 weeks prior. He had no underlying disease. The patient had taken sildenafil citrate on 3 different occasions 2 weeks prior, and 2 days after his first ingestion, his right conjunctiva was injected and binocular diplopia started. On the first visit, he showed 16 PD hypotropia of the right eye with limitation of motion at upgaze. The MRI scan showed enlargement and enhancement of the inferior rectus muscle, and 50 mg of prednisone was prescribed. The amount of hypotropia decreased to 8 PD 2 weeks later.

Enlargement of extraocular muscle caused by sildenafil citrate ingestion has not been reported in Korea, and related mechanisms are yet to be researched. Additional case reports and research are necessary in the future.