Medical backgrounders: glaucoma

Abstract

Glaucoma is a leading cause of irreversible blindness in the world. Currently, glaucoma is diagnosed as a progressive optic neuropathy with characteristic optic disc and nerve fiber layer damage, usually associated with loss of visual function. The intraocular pressure (IOP) is the most important risk factor for the disease, although a significant proportion of patients do not have elevated IOP. Other risk factors include older age, African descent, myopia and family history of the disease. The ophthalmoscopic examination of the optic disc is essential to identify the signs of glaucomatous optic neuropathy, such as increased cupping, neuroretinal rim thinning or optic disc hemorrhages. Glaucomatous visual field loss usually starts in the periphery, and loss of central vision does not occur until late in the course of the disease. Visual function is most commonly assessed by standard automated perimetry; however, as many as 50% of nerve fibers can be lost before the appearance of visual field defects in this test. Newer technologies have been developed to find more sensitive ways to detect early glaucoma using both functional (short-wavelength automated perimetry and frequency-doubling perimetry) and structural (scanning laser topography, optical coherence tomography and scanning laser polarimetry) measurements. The management of glaucoma is based on lowering the intraocular pressure to prevent further optic nerve damage. Currently, there are five major classes of medications that are used to lower the intraocular pressure: Beta-adrenergic antagonists, adrenergic agonists, parasympathomimetics, prostaglandin-like analogues and carbonic anhydrase inhibitors. The goal of therapy is to maintain adequate vision for patients during their lifetime, keeping in mind the possible adverse effects of the drugs. If additional lowering of IOP is indicated or if medication fails to sufficiently lower the IOP, laser trabeculoplasty is usually the next step. If IOP is still not adequately controlled, incisional glaucoma surgery is indicated. Neuroprotective agents, which directly protect the optic nerve in glaucoma, are being evaluated in clinical trials.