Glaucoma

Glaucoma is a disease characterized by elevated intraocular pressure, optic nerve damage, and subsequent impaired vision. Glaucoma is one of the leading causes of adult blindness in the United States and worldwide. Risk factors include increased age, African-American race, and family history in a first-degree relative. The main types of glaucoma include primary open angle glaucoma, angle closure glaucoma, and congenital glaucoma. Primary open angle glaucoma is the most common form of glaucoma and occurs in 0.5 to 2.1 percent of the population over the age of 40. It is caused by a resistance to flow of aqueous humor. Aqueous humor is produced in the ciliary body and drained by the trabecular meshwork. Dysfunction of the trabecular meshwork leads to a disruption in the normal flow of aqueous humor. This results in an increase in the pressure of the eye and damage to the optic nerve. The increased pressure causes a decrease in the blood supply to the nerve and thus damage to the nerve. Over time, due to the damage to the nerve, patients will gradually lose peripheral vision. In advanced cases, the vision loss can lead to absolute blindness.

Angle closure glaucoma results from the peripheral iris, or colored part of the eye, blocking the trabecular meshwork. The angle closure leads to a rise of the in [Page 741]traocular pressure from its normal level (10 to 21 mm Hg) to 30 mm Hg or more. This results in an increase in aqueous fluid inside the eye causing damage to the optic nerve. Prodromal symptoms occur as transitory attacks during which time patients may experience symptoms of decreased vision, eye pain, halos around lights, headache, nausea, and vomiting.

Glaucoma is one of the leading causes of adult blindness in the United States and worldwide.

Another important type of glaucoma is congenital or infantile glaucoma. Congenital glaucoma has an incidence of 1 in 10,000 births with an increased incidence in males. The exact cause is unknown but appears related to a maldevelopment of the aqueous humor drainage system. Signs and symptoms include enlarged cornea (buphthalmos), photophobia, and tearing. Prompt surgical intervention offers the best method of controlling the intraocular pressure and long-term preservation of vision.

For the adult patient, the first signs of glaucoma include gradual loss of peripheral vision. Patients with angle closure glaucoma may present with pain and colored halos, but with primary open-angle glaucoma, patients may be asymptomatic until late in the disease. Glaucoma screening involves a complete ophthalmic history and examination, including evaluation of intraocular pressures, optic nerve, visual fields, and gonioscopy (evaluation of the drainage system of the eye). Intraocular pressure in most individuals ranges between 10 and 21 mmHg, with an average of approximately 16 mmHg. Patients with pressures above 21 are suspicious for glaucoma. Intraocular pressures can fluctuate throughout the day, so pressure levels cannot be the only screening tool for glaucoma.

During examination, the optic nerve is also observed. The optic nerve is examined by comparing the cup to disk ratio. A central depression exists in the optic nerve called the cup. An increase in the size of the cup relative to the rest of the nerve signifies glaucomatous damage. Physical examination should also include gonioscopy. Gonioscopy consists of a special lens placed on the eye that allows visualization of the trabecular meshwork, peripheral iris, cornea, and presence of angle closure. For patients with glaucoma, management includes intraocular pressure checks every three to six months, visual field examination every six to 12 months, gonioscopy and optic nerve evaluation yearly.

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