An Introduction to Glaucoma for the Non-Opthalmic Doctor
Glaucoma is a group of eye diseases which in most cases produce increased intraocular pressure (IOP), which over time causes damage to the optic nerve. Through early detection and treatment, vision can be saved most of the time.
The aqueous humor is constantly circulating through the anterior chamber. It is produced by the ciliary body, situated behind the iris (Fig 1).
It flows between the iris and the lens and, after nourishing the cornea and lens, flows out through a spongy tissue, the trabecular meshwork, which serves as the drain of the eye. The trabecular meshwork is situated in the angle where the iris and cornea meet. When this drain becomes clogged, aqueous can not leave the eye as fast as it is produced, causing the fluid to back up. We call this open angle glaucoma. In angle closure glaucoma, on the other hand, the aqueous cannot actually reach its drainage site due to blockade at the iridocorneal angle, weather acute (appositional) or chronic (synechial).
To understand how increased IOP leads to glaucoma, remember that the adult eyeball wall is non-expandable so it gives away at the weakest point, which is the site in the sclera at which the optic nerve leaves. We call this the lamina cribrosa and it harbors most of the clinical signs of glaucoma (Fig 2). The optic nerve is part of the central nervous system and carries visual information from the eye to the brain. This cranial nerve is made up of over one million nerve axons, which are nerve fiber extensions of the retinal ganglion cells. When IOP is increased and/or other inciting factors exist, the optic nerve becomes damaged and the retinal ganglion cells undergo slow apoptosis. The death of the retinal ganglion cells and degeneration of the nerve fibers results in permanent vision loss. Early diagnosis and treatment of glaucoma can help prevent blindness.