Glaucoma

Appearance of the eye in acute glaucomaAppearance of the eye in acute glaucoma– A disorder in which increased intraocular pressure leads to eventual vision impairment and possibly to degeneration of the optic nerve. It may be primary or occur secondary to other ocular disease. Glaucoma is classified as open or closed angle.

Causes and Incidence

The etiology of primary glaucoma is unknown, but predisposing factors include heredity, hyperopia, and vasomotor instability. It is estimated that 1.5% to 2% of Americans over 40 years of age have glaucoma, and more than 12% of newly diagnosed cases of blindness are attributable to glaucoma. Blacks and those with a family history are most susceptible. Ninety percent of primary glaucoma cases are the open-angle type, which occurs most often after age 65.

Disease Process

Increased intraocular pressure (IOP) is related to an imbalance in the production, inflow, and outflow of aqueous humor. Inflow occurs through the pupil and outflow through the meshwork at the juncture of the iris and cornea. In secondary glaucoma the meshwork becomes clogged by blood, fibrin, or inflammatory cells produced by an underlying ocular disorder. Primary open-angle glaucoma is marked by degenerative changes to the meshwork that block outflow. In primary closed-angle glaucoma, the anterior chamber is shallow, the filtration angle is narrow, and the iris obstructs the meshwork at Schlemm’s canal. Sometimes dilation of the pupil or trauma pushes the iris forward, narrowing the angle and resulting in obstruction in an acute attack. Primary or secondary glaucoma may be congenital; the condition is hereditary (primary) or is caused by fetal defects in the ocular structure or underlying congenital systemic disorders (secondary).

Symptoms

Open angle
Often asymptomatic; frequent changes in prescription for glasses; mild headaches, vague visual disturbances; halos around lights; difficulty adjusting to darkness

Closed angle
Severe pain in and around eye; tearing; colored rainbow halos around lights; recurring episodes of blurring and impaired vision; mild dilation of pupils; hazy cornea; possible nausea and vomiting

Potential Complications

Untreated glaucoma leads to progressively diminishing vision, degeneration of the optic nerve, and blindness.

Diagnostic Tests

Tonometry
To measure elevation in IOP

Visual field studies
To detect impairment in central and peripheral visual fields

Gonioscopy
To detect cellular debris or adhesions and differentiate openangle from closed-angle type

Ophthalmoscopy
To visualize optic nerve

Treatments

In secondary glaucoma, treatment focuses on the underlying disease process, in conjunction with mydriasis.

Surgery
Open angle: laser/external trabeculoplasty to improve drainage if medications fail; placement of filtering devices if trabeculoplasty fails.

Closed angle: laser iridotomy/peripheral iridectomy to push iris back and increase angle.

Ocular implants for some complex forms of glaucoma.

Drugs
Open angle: betaadrenergic blockers and diuretics to reduce production of aqueous humor, miotics to reduce pressure, and adrenergics to increase aqueous outflow.

Closed angle: hyperosmotic agents, carbonic anhydrase inhibitors, and miotics to reduce pressure or abort acute attack; narcotic analgesics for pain.

General
Open angle: avoidance of tobacco use, fatigue, emotional upset, and ingesting large quantities of fluid; instruction in instillation of eye drops, and long-term use of medications and their side effects.