Optineurin (OPTN) has recently been linked to glaucoma, a major cause of blindness worldwide. Mutations in OPTN such as Glu50-->Lys (E50K) have been reported in patients, particularly those with normal pressure glaucoma. Here, we show that the endogenous OPTN was not secreted in two ocular cell types, human trabecular meshwork and retinal pigment epithelial cells. It localized instead in the cytoplasm in a diffuse pattern without a distinct association with the Golgi apparatus. When overexpressed, however, wild-type OPTN-green fluorescent protein (GFP) formed foci especially around the Golgi, colocalizing partially with the common endocytic pathway marker transferrin receptor in both cell types. Fragmentation of the Golgi was also observed. On nocodazole treatment, the OPTN foci were dispersed into the cytoplasm. Overexpression of mutant OPTNE50K-GFP resulted in a greater number (P<0.0055) and size of the foci, compared with the wild type, and the Golgi alteration was potentiated. Cell loss observed in OPTN-expressing cultures was also more pronounced in OPTNE50K-GFP compared with that of wild-type OPTN-GFP counterparts (P<0.01). This study highlights a possible role of OPTN in vesicle trafficking and Golgi integrity. It also provides in-sights into the possible mechanisms why E50K would exhibit a propensity toward the development of glaucoma.