Enlargement of levator palpebrae superioris muscle fibers in Graves' ophthalmopathy.

Enlargement of the extraocular muscles in Graves' ophthalmopathy is attributed to inflammation and fibrosis. This is the first report of the histology and morphometry of the levator palpebrae superioris (LPS) muscle proximal to Whitnall's ligament in Graves' ophthalmopathy. Four thousand computer-assisted levator muscle fiber measurements in 16 control and abnormal levator palpebrae superioris muscle biopsies were done. These measurements showed statistically significant levator muscle fiber enlargement in the Graves' ophthalmopathy specimens. There was minimal evidence of inflammation. These findings suggest that muscle fiber enlargement is an important cause of the characteristic hypertrophy of the levator muscle in Graves' ophthalmopathy. Levator muscle fiber enlargement is a likely cause of upper eyelid retraction in Graves' ophthalmopathy.