In his review, Dr. Lin, professor of ophthalmology, co-director of the glaucoma service, University of California San Francisco, and director of the glaucoma service, San Francisco General Hospital, discussed evidence for the use of calcium-channel blockers, beta-blockers, supplemental calcium and iron restriction, memantine, brimonidine, copolymer-1, and ginkgo biloba.
Understanding of the role of extracellular calcium transport across cell membranes in modulating various intracellular signaling processes, including the initiation of the apoptotic cascade, represents part of the rationale for interest in investigating calcium-channel blockers for neuroprotection in glaucoma. As reviewed by Araie et al. [Prog Eye Res. 2011;30:54-71], results of some clinical studies suggest calcium-channel blockers may have some efficacy as neuroprotection for normal-tension glaucoma, said Dr. Lin.
"These studies were primarily conducted in Japan where about 80% of glaucoma is of the normal-tension type and so there is great interest in finding alternatives to IOP-lowering treatment. However, one must also consider whether any positive effect associated with the calcium-channel blocker treatment can be extrapolated to other patient populations," he commented.
Some beta-blockers, particularly betaxolol, also show substantial calcium-channel blocking activity, and a review of clinical studies investigating topical betaxolol and timolol treatment found betaxolol was associated with better visual field preservation than timolol, despite having a less potent IOP-lowering effect [Prog Retin Eye Res. 2010;29:79-93]. However, the studies providing this evidence are mostly small or retrospective, said Dr. Lin.
The possible role of excessive calcium in retinal ganglion cell apoptosis raises the question of whether there is an association between glaucoma and supplemental calcium intake, and Dr. Lin credited Sophia Wang, BS, a UCSF medical school student doing research with him, for a study to investigate this idea [Invest Ophthalmol Vis Sci. 2012;13:53:725-731]. Data were extracted from nearly 4,000 participants in the National Health and Nutrition Examination Survey for 2007 and 2008 on diagnosis of glaucoma and use of calcium supplements as well as iron, which like calcium, has oxidant activity.