The Trabecular Meshwork: A Basic Review of Form and Function

Glaucoma is a group of optic neuropathies in which damage to the optic nerve results in a distinctive pattern of irreversible vision loss. Elevations in the intraocular pressure (IOP) are a common contributor to this damage. This major cause of blindness affects mainly the elderly population. Over 70 million people are diagnosed with glaucoma worldwide and over 4 million have lost vision in both eyes [1-5]. The overall prevalence of open angle glaucoma is estimated to be 3.54% [6]. Glaucoma accounts for around 25% of new blindness in developed countries [3,7]. Primary open-angle glaucoma (POAG) is the most common form and constitutes up to 85% of diagnosed cases. The risk factors include elevated IOP, age, genetic factors, race, thin corneas and abnormal optic nerve anatomy [7]. Glaucoma is normally asymptomatic and is usually not detected until significant irreversible vision loss, which is primarily peripherally located in the field of view, has taken place. The therapeutic management of glaucoma costs the United States and the United Kingdom about 2.5 billion and 216 million USD annually, respectively [8,9]. IOP is a consequence of aqueous humor inflow balanced against aqueous humor outflow and both are approximately 2.75 μl/min [10]. Inflow is relatively pressure insensitive until very high pressures are achieved [11]. IOP is regulated primarily by controlled adjustments of the outflow resistance which resides in the trabecular meshwork (TM) [12,13]. Since the eye is a single hydraulic unit, pressure everywhere within the eye is uniform and IOP elevations impact the optic nerve directly, since it is most vulnerable to pressure.