Intraocular pressure variations: causes and clinical significance.

Reduction of intraocular pressure (IOP) is the only known effective treatment for glaucoma. However, IOP is a highly variable and dynamic parameter, undergoing virtually constant changes from numerous factors, including body position and circadian rhythms. Despite this variability, evidence for the efficacy of IOP reduction in glaucoma is based on studies designed to assess mean IOP and not IOP variations. Post hoc analysis of data from major clinical trials has suggested that IOP variations may be an independent risk factor for the development of glaucoma or glaucomatous progression, at least in some patients, but the evidence is incomplete and further studies are required. In the interim, judicious selection of existing therapies can help to minimize IOP variations. In general, therapies that improve outflow instead of suppressing aqueous humor production result in more stable IOP. However, new technology to allow better monitoring of IOP, ideally in a continuous 24-hour manner, is required to fully understand the role of IOP variations in glaucoma.