Glaucoma is not a single disorder, but rather multiple disorders (Table 1). There are multiple classification schemes. Glaucoma can be classified into congenital glaucoma, primary glaucoma, and secondary glaucoma. Congenital glaucoma is caused by an abnormality in the aqueous humor outflow tract in the anterior chamber. There may be other associated developmental ocular abnormalities. Primary glaucoma is divided into two categories, primary open angle glaucoma, and primary closed angle glaucoma. Primary open angle glaucoma is the most common form of glaucoma . It is caused by chronic obstruction of outflow of aqueous humor from the anterior chamber through the trabecular network. The angle between the iris and the cornea is open and there is free passage of aqueous humor from the posterior chamber to the anterior chamber. The reported causes of obstruction at the level of the trabecular network are multiple and include accumulation of debris in the trabecular network, loss of the normally functioning trabecular cells, loss of permeability of the trabecular network, loss of the normal trabecular cleaning mechanism, and poor drainage through the canal of Schlemm due to a loss of adequate spaces. Primary closed angle glaucoma is caused by sudden increase in intraocular pressure due to blockade of aqueous humor flow from the posterior chamber because of pupillary block. Secondary glaucoma is an increase in intraocular pressure due to trauma, hemorrhage, infection, tumor, or surgical procedures.
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