– 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.
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).
Often asymptomatic; frequent changes in prescription for glasses; mild headaches, vague visual disturbances; halos around lights; difficulty adjusting to darkness
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
Untreated glaucoma leads to progressively diminishing vision, degeneration of the optic nerve, and blindness.
To measure elevation in IOP
Visual field studies
To detect impairment in central and peripheral visual fields
To detect cellular debris or adhesions and differentiate openangle from closed-angle type
To visualize optic nerve
In secondary glaucoma, treatment focuses on the underlying disease process, in conjunction with mydriasis.
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.
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.
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.