Previous experimental and clinical investigations have suggested that some patients with primary open-angle glaucoma may have an abnormally low orbital cerebrospinal fluid pressure (CSFP). A meta-analysis of available clinical data showed a marked overlap in lumbar CSFP measurements between patients with normal-tension glaucoma and healthy subjects, so that the question arises as to which additional factors play a role in the pathogenesis of glaucomatous optic neuropathy.