Glaucoma
A group of disorders, glaucoma is characterized by high intraocular pressure (IOP) that damages the optic nerve. Glaucoma may occur as a primary or congenital disease or secondary to other causes, such as injury, infection, surgery, or prolonged topical corticosteroid use.
Primary glaucoma has two forms: open-angle (also known as chronic, simple, or wide-angle) glaucoma and angle-closure (also known as acute or narrow-angle) glaucoma. Angle-closure glaucoma attacks suddenly and may cause permanent vision loss in 48 to 72 hours.
One of the leading causes of blindness, glaucoma affects about 2% of Americans older than age 40 and accounts for about 12% of newly diagnosed blindness in the United States. The incidence is highest among Black and Asian populations. In the United States, early detection and effective
treatment contribute to the good prognosis for preserving vision.
treatment contribute to the good prognosis for preserving vision.
Causes
Open-angle glaucoma results from degenerative changes in the trabecular meshwork that block the flow of aqueous humor from the eye, thereby causing increased IOP. The result is optic nerve damage. Affecting about 90% of all patients who have glaucoma, open-angle glaucoma commonly occurs in families.
Angle-closure glaucoma results from obstruction to the outflow of aqueous humor caused by an anatomically narrow angle between the iris and the cornea. This causes a sudden increase in IOP. Angle-closure glaucoma attacks may be triggered by trauma, pupillary dilation, stress, or any ocular change that pushes the iris forward (a hemorrhage or a swollen lens, for example).
Secondary glaucoma can proceed from such conditions as uveitis, trauma, drug use (such as corticosteroids), venous occlusion, or diabetes. In some cases, new blood vessels (neovascularization) may form, blocking the passage of aqueous humor.
Complications
If untreated, glaucoma can progress from gradual vision loss to total blindness.
Assessment
Inspection may reveal unilateral eye inflammation, a cloudy cornea, and a moderately dilated pupil that’s nonreactive to light. Palpation may also disclose increased IOP discovered by applying gentle fingertip pressure to the patient’s closed eyelids. With angle-closure glaucoma, one eye may feel harder than the other. (See How glaucoma progresses.)
Diagnostic tests
Tonometry (with an applanation, Schiøtz, or pneumatic tonometer) measures IOP and provides a baseline for reference. Normal IOP ranges from 8 to 21 mm Hg. However, patients whose pressures fall within the normal range can develop signs and symptoms of glaucoma, and patients who have abnormally high IOP may have no clinical effects.
Slit-lamp examination allows the physician to see the effects of glaucoma on the anterior eye structures, including the cornea, iris, and lens.
Gonioscopy determines the angle of the eye’s anterior chamber. This enables the physician to distinguish between open-angle and angle-closure glaucoma. The angle is normal in open-angle glaucoma. In older patients, however, partial closure of the angle may occur (allowing two forms of glaucoma to coexist).
