Methylmalonicaciduia(MMA)accompanied with homocystinuria is a rare autosomal-recessive with congenital metabolic disorder of Vitamin B12. There are three subtypes, cblC, cblD, cblF, in which cblC is the most common one. The diagnostic tests are tandem mass spectrometry and gas chromatography-mass spectrometry. Tests for activity of enzyme in fibroblasts from skin, complementary assay and genetic analysis can be used to make the subtype clear. Early-onset patients, defined by onset of symptoms before the age of 1 year, may have severe ocular involvement, including visual loss, nystagmus, strabismus, retinopathy, maculopathy, optic atrophy, abnormal electroretinography. Late-onset patients, defined by onset of symptoms after the age of 4 year, rarely have ocular manifestations. The pathogenesis of the ophthalmic symptoms may be related to the high level of homocystine, oxidative stress and the abnormal development of nervous systems. The treatment for MMA accompanied with homocystinuria is mostly symptomatic based. Ophthalmic treatment is limited. Early supplement of methionine,GSH or other antioxidants may be helpful for retinopathy. There is no standard ophthalmological examination for those patients in China. It is critical to set up inter-departmental cooperation and early stage examination for the treatments and outcomes of the patients.