Senescent changes in cerebrospinal fluid circulatory physiology and their role in the pathogenesis of normal-tension glaucoma.

PURPOSE To evaluate the evidence supporting a role for senescent changes in cerebrospinal fluid (CSF) circulatory physiology in the pathogenesis of normal-tension glaucoma (NTG). DESIGN Literature review and personal perspective of the authors. METHODS Analysis of selected articles in the peer-reviewed literature with interpretation and perspective. RESULTS Recent studies have reported that intracranial pressure is lower in patients with NTG when compared with patients with primary open-angle glaucoma and nonglaucomatous control subjects. It has been suggested that a low intracranial pressure in patients with normal intraocular pressure could lead to glaucomatous damage. This low intracranial pressure, leading to an abnormally high trans-lamina cribrosa pressure difference, could result in barotraumatically induced optic nerve damage at the lamina cribrosa. However, several experimental studies do not support the speculation that low intracranial pressure and the resulting pressure-dependent effects cause bowing back of the lamina cribrosa and optic disc cupping. On the other hand, CSF production and turnover have been shown to be decreased in aging and in pathologic conditions, such as Alzheimer disease and normal pressure hydrocephalus. Interestingly, recent studies have revealed that both Alzheimer disease patients and patients with normal pressure hydrocephalus may have a higher risk of developing glaucoma. Therefore, we believe that CSF circulatory failure, ultimately resulting in reduced neurotoxin clearance along the optic nerves, could be an alternative explanation as to why glaucoma develops in patients with low intracranial pressure. CONCLUSIONS On the basis of the evidence available from the peer-reviewed literature, our tentative conclusion is that age-related changes in CSF circulatory physiology and the subsequent decrease in CSF turnover, with diminished clearance of toxic substances, can account for, at least in part, the pathogenesis of NTG. It should be stressed that for the moment at least, the present hypothesis remains unproven. Further research will be necessary to determine the possible role of CSF circulatory dysfunction in NTG. If confirmed, this hypothesis could provide new, important insights into the pathogenesis of NTG.