Chapter 32

Glaucoma is a disorder characterized by damage to the optic nerve that, if untreated, leads to progressive loss of vision. In children it is almost always caused by increased intraocular pressure (IOP). Glaucoma is one of the leading causes of visual loss in adults, but is rare in children. Estimates of the incidence of primary infantile glaucoma range from 1 in 2,500 to 1 in 22,000.

Glaucoma may be classified as primary or secondary. Primary glaucoma is caused by an underlying disorder of aqueous fluid outflow from the eye. Secondary glaucoma occurs due to a variety of ocular defects that lead to increased IOP.

Glaucoma may also be classified as open angle or closed angle (Figure 32–1). This refers to whether or not the trabecular meshwork is visible when viewed with a goniolens, an instrument that allows the examiner to visualize the fluid outflow pathways. Open angle glaucoma is much more common. In this condition, the pressure increases due to resistance within the outflow pathways, usually caused by microscopic alterations within the trabecular meshwork. In closed-angle glaucoma, access to the trabecular meshwork is blocked. This is usually caused by forward movement of the iris. This may occur for a variety of reasons, including a mass growing behind the iris (e.g., retinoblastoma), scarring of the pupil margin causing fluid to build up behind the iris and push it forward (as may occur in iritis), or in patients with very small eyes (nanophthalmos).

###### FIGURE 32–1

Fluid in the eye is produced by the ciliary body. It flows around the iris and drains into the trabecular meshwork. Top: In closed-angle glaucoma, the fluid cannot reach the trabecular meshwork, usually because the iris tissue moves forward and obstructs the flow. Bottom: In open-angle glaucoma, microscopic obstruction is present within the trabecular meshwork itself, which impedes flow, resulting in increased intraocular pressure.

Normal ocular pressure is maintained by a balance of fluid (aqueous humor) production by the ciliary body and fluid outflow through the trabecular meshwork (Figures 32–2 and 32–3A and B). Glaucoma virtually always results from obstructed outflow, rather than fluid overproduction. When the IOP is elevated, the optic nerve is damaged by compression against the sclera, resulting in loss of the ganglion cells that form the optic nerve. This initially affects the upper and lower fibers on the lateral side of the optic nerve, causing loss of vision in an arcuate pattern above and below the center of vision. If untreated, progressive constriction of the visual field occurs, ultimately affecting central vision late in the disease. Patients may not notice the peripheral loss initially, and therefore they may remain asymptomatic until substantial damage has occurred.

###### FIGURE 32–2

Glaucoma causes increased intraocular pressure, which in ...

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