Eyes with normal-pressure glaucoma and those with high-pressure glaucoma can show a similar optic nerve head appearance, while eyes with vascular optic neuropathies show a markedly different optic disc appearance. Factors in addition to intraocular pressure (IOP) may thus play a role in the pathogenesis of glaucomatous optic neuropathy. Clinical and experimental studies showed that (1) physiologic associations between cerebrospinal fluid (CSF) pressure, systemic arterial blood pressure, IOP and body mass index exist; (2) a low CSF pressure was associated with the development of glaucomatous optic nerve damage in cats; (3) patients with normal (intraocular) pressure glaucoma had significantly lower CSF pressure and a higher trans lamina cribrosa pressure difference when compared to normal subjects; and (4) patients with normal- pressure glaucoma as compared with patients with high-pressure glaucoma have a significantly narrower orbital CSF space. A shallow orbital CSF space has been shown to be associated with a low CSF pressure. Due to anatomic reasons, the orbital CSF pressure and the optic nerve tissue pressure (and not the atmospheric pressure) form the retro-laminar counter-pressure against the IOP and are thus part of the trans-lamina cribrosa pressure difference and gradient. Assuming that an elevated trans-lamina cribrosa pressure difference and a steeper trans-lamina cribrosa pressure gradient are important for glaucomatous optic nerve damage, a low orbital CSF pressure would therefore play a role in the pathogenesis of normal-(intraocular) pressure glaucoma. Due to the association between CSF pressure and blood pressure, a low blood pressure could be indirectly involved.