Neuroprotection in glaucoma.
Currently, glaucoma is recognised as an optic neuropathy. Selective death of retinal ganglion cells (RGC) is the hallmark of glaucoma, which is also associated with structural changes in the optic nerve head. The process of RGC death is thought to be biphasic: a primary injury responsible for initiation of damage that is followed by a slower secondary degeneration related to noxious environment surrounding the degenerating cells. For example, retinal ishaemia may establish a cascade of changes that ultimately result in cell death: hypoxia leads to excitotoxic levels of glutamate, which cause a rise in intra-cellular calcium, which in turn, leads to neuronal death due to apoptosis or necrosis. Neuroprotection is a process that attempts to preserve the cells that were spared during the initial insult, but are still vulnerable to damage. Although not yet available, a neuroprotective agent would be of great use in arresting the progression of glaucoma. There is evidence that neuroprotection can be achieved both pharmacologically and immunologically. Pharmacological intervention aims at neutralising some of the effects of the nerve-derived toxic factors, thereby increasing the ability of the spared neurons to cope with stressful conditions. On the other hand, immunological interventions boost the body's own repair mechanisms for counteracting the toxic effects of various chemicals generated during the cascade. This review, based on a literature search using MEDLINE, focuses on diverse cellular events associated with glaucomatous neurodegeneration, and discusses some pharmacological agents believed to have a neuroprotective role in glaucoma.