SUMMARY
We investigated the morphological differences among normal extraocular muscles (EOM), normal skeletal muscle and pathological skeletal muscle. The EOM came from seven patients submitted to retinoblastoma surgery. The skeletal muscle came from normal male adults, and from patients with primary myopathy: congenital muscular dystrophy (17), mitochondrial myopathy (12), nemalinic myopathy (4) and myotonic distrophy (4). The diagnosis of mitochondrial myopathy was defined by morphological criteria (presence of ragged red fibers in muscle - biopsy specimens stained with modified Gomori's trichrome stain). This study revealed a marked difference among these muscles. There was a significantly higher oxidative metabolism in EOM than in others muscles, an unexpected pattern. We concluded that EOM has specific histochemical features, but the morphological criteria to individualize specific disease has not been defined.