Objective To investigate the clinical manifestations,pathological characteristics of mitochondrial encephalomyopathy with the mainly symptoms in the eye.Methods Clinical manifestations and pathological changes were analyzed in 12 patients with chronic progressive external opthalmoplegia (CPEO) and 2 patients with kearns-sayre syndrome.Results:In 14 patients,8 were male and 6 female.The average age of onset was 1 1.5 years old,2 were siblings.All patients showed chronic progressive ptosis and difficulty in eye movements.All were symmetric except 2 at early stage.Besides ophthalmoplegia,5 had orbicularis weakness,1 had mild limb weakness,1 had auditory defect,2 had retinitis pigmentosa,3 had endocrine disfunction.Ragged-red fiber (RRF) positive muscle fibers and cytochnome cxidase (COX) deficient muscle fibers were increased in all specimens of muscle biopsies.Conclusions The major clinical manifestation of CPEO and kss is progressive ophthalmoplegia,which can be accompanied by limb weakness,retinitis pigmentosa,deafness,heart conduction defect,endocrine dysfunction,etc.Ragged red fibers and COX deficiency fibers would be crucial pathological clues for the diagnosis of CPEO and Kss.