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[Gr., glaukōma, opacity of the lens (of the eye), cataract]
Any of a group of eye diseases characterized by increased intraocular pressure, resulting in atrophy of the optic nerve, and loss of visual fields.
SEE: visual field for illus.
Glaucoma is the third most prevalent cause of visual impairment and blindness in the U.S., but the incidence of blindness is decreasing due to early detection and treatment. It is the second most common cause of blindness internationally. Worldwide, approx. 60 million people have glaucoma.
Glaucoma occurs when the aqueous humor drains from the eye too slowly to keep up with its production in the anterior chamber. Thus, narrowing or closure of the filtration angle that interferes with drainage through the canal of Schlemm causes intraocular fluid to accumulate, after which intraocular pressure increases. Glaucoma may develop, however, even if the filtration angle is normal and the canal of Schlemm appears to be functioning. The cause of this form of glaucoma is not known.
SYMPTOMS AND SIGNS
Glaucoma causes gradual loss of peripheral vision, and, ultimately, blindness. The three major categories of glaucoma are narrow- or closed-angle (acute) glaucoma, which occurs in those whose eyes are anatomically predisposed to develop the condition; open-angle (chronic) glaucoma, in which the angle that permits the drainage of aqueous humor from the eye seems normal but functions inadequately because of overproduction of aqueous humor or obstruction of outflow through the trabecular meshwork or through the canal of Schlemm; and congenital glaucoma, in which intraocular pressure is increased because of an abnormal fluid drainage angle (a possible result of congenital infections, Sturge-Weber syndrome, or prematurity-related retinopathy), or for an unknown reason. The increased pressure causes the globe of the eye to be enlarged (buphthalmia). The acute type of glaucoma is often attended by acute pain. The chronic type has an insidious onset. An initial visual dysfunction is loss of the midperipheral field of vision. The loss of central visual acuity occurs later in the disease.
Isolated elevations in intraocular pressure (IOP) and early glaucoma may cause no symptoms. Open-angle glaucoma may cause mild eye pain, gradual but progressive loss of peripheral vision, haloes around lights, and reduced visual acuity (esp. at night) that is not corrected by prescription lenses. Acute angle-closure glaucoma (an ophthalmic emergency) causes excruciating unilateral pain and pressure, blurred vision, decreased visual acuity, haloes around lights, diplopia, lacrimation, and nausea and vomiting due to increased IOP. The eyes may show unilateral circumcorneal injection, conjunctival edema, a cloudy cornea, and a moderately dilated pupil that is nonreactive to light. Acute angle-closure glaucoma requires immediate treatment to reduce IOP.
Elevated IOP can be detected early by measurements made by optometrists or ophthalmologists. IOP measurements may require adjustment of the raw values that are obtained for changes in corneal thickness (as demonstrated with a pachymeter or with optical coherence tomography). A normal tonometer reading ranges from 13 to 22 mm Hg. The standard for determining visual loss (as opposed to the intraocular pressure) in glaucoma is the visual-field test.
Nonoperative treatment of open-angle glaucoma includes topical miotics (such as pilocarpine), beta blockers (such as timolol maleate), and prostaglandin analogues (such as travoprost or latanoprost). Marijuana alleviates the symptoms of severe glaucoma by lowering the IOP. Control of associated disorders such as diabetes mellitus should be maintained. Operative treatment includes laser trabeculoplasty, surgical trabeculectomy, viscocanalostomy, and deep sclerectomy. Side effects of trabeculectomy include postoperative hypotony, cataract formation, and choroidal detachment. Side effects of topical agents include browning of the cornea (the prostaglandin analogues) and ocular redness.
GLAUCOMA ; SEE: ciliarotomy; SEE: trabeculoplasty
Acute glaucoma may be precipitated in patients with closed-angle glaucoma by dilating the pupils. In glaucoma patients, cycloplegic drops are given only after trabeculectomy and only in the eye that had the procedure. Administering drops in an eye affected with glaucoma can precipitate an acute attack in an eye already compromised by elevated IOP.
Health care providers should wash their hands thoroughly before touching the patient's eye. Prescribed topical and systemic medications are administered and evaluated.
The patient is prepared physically and psychologically for diagnostic studies and surgery as indicated. If the patient has a trabeculectomy, prescribed cycloplegic drugs are administered to relax the ciliary muscle and decrease iridic action, thus reducing inflammation and preventing development of adhesions. Mitomycin C, given intraoperatively, reduces IOP more than surgery alone.
After any surgery, an eye patch and shield are applied to protect the eye; the patient is positioned with the head slightly elevated, and general safety measures geared to the patient's level of sensory alteration are instituted. Usually, the patient is encouraged to ambulate as soon as possible after surgery.
Patients with glaucoma need to know that the disease can be controlled but not cured. Fatigue, emotional upsets, excessive fluid intake, and use of antihistamines may increase IOP. Signs and symptoms such as vision changes or ocular pain should be reported immediately. Both the patient and family are instructed in correct techniques for hand hygiene and administration of eyedrops; the importance of adherence to the prescribed regimen; the need for regular follow-up care with an ophthalmologist; and any adverse reactions to report.
Information is provided to the patient and family as needed. Referral is made to local organizations and support groups.
Public education is carried out to encourage glaucoma screening for early detection of the disease. Because glaucoma is more common in African Americans than European Americans, all African Americans above age 40 (and earlier for those with a family history of glaucoma) should have an annual tonometric examination. Written information should be made available about detection and control of glaucoma.