Glaucoma is a serious and progressive EYE condition in which the cells at the front of the OPTIC NERVE where it intersects with the RETINA, the retinal ganglia, die, resulting in vision loss. Early diagnosis and treatment can minimize vision loss. Health experts estimate that 5 million Americans have glaucoma, though only about 2 million of them know it. Glaucoma is the third-leading cause of blindness in the United States, primarily because it remains undetected until damage to the optic NERVE becomes significant. Glaucoma becomes more common after age 65, though there is a congenital form that manifests in early childhood (congenital glaucoma).
Until the late 1990s ophthalmologists perceived glaucoma to be the exclusive consequence of increased pressure within the eye (INTRAOCULAR PRESSURE) that caused the death of retinal ganglia cells. Current understanding of the disease process of glaucoma affirms the death of retinal ganglia cells as the cause of damage to the optic nerve, though recognizes that numerous factors, intraocular pressure being only one among them, contribute to this damage. About 30 percent of people who have glaucoma have normal intraocular pressure, and only about 10 percent of people who have elevated intraocular pressure have glaucoma.
There are two general forms of glaucoma: open angle and closed angle (also called angle-closure). The designations refer to whether the channel through which aqueous humor drains from the eye, called the angle, is open but dysfunctional (open-angle glaucoma) or becomes blocked by the iris (closed-angle glaucoma). In glaucoma, the drainage angle either malfunctions (open-angle glaucoma) or a segment of the iris seals over it (closed-angle glaucoma). When the aqueous humor cannot properly drain, it causes the pressure to increase in the anterior chamber. Increased pressure in the chambers puts increased pressure on the inner eye, causing intraocular pressure to rise. Extreme or extended elevations in intraocular pressure compress the optic disk, causing nerve cells to die.
Acute closed-angle glaucoma requires emergency medical attention. Without immediate treatment, severe to complete vision loss can occur within hours of the onset of symptoms.
Open-angle glaucoma is chronic, progressing over years, and is the most common form of glaucoma, accounting for about 85 percent. Closedangle glaucoma can be acute, with the sudden onset of severe symptoms, or chronic with symptoms similar to those of open-angle glaucoma. The function and dysfunction of aqueous humor drainage is the dimension of glaucoma doctors and researchers understand most clearly, and most treatment approaches target reducing aqueous humor production or improving its drainage from the eye. Less clear are the other factors that contribute to death of the retinal ganglia cells and corresponding destruction of the optic disk. These factors are especially significant for the 30 percent of people who have glaucoma with normal intraocular pressure. Researchers are investigating the roles of genetics, autoimmune processes, and correlations with conditions such as DIABETES and HYPERTENSION (high BLOOD PRESSURE).
The key symptom of chronic glaucoma, openangle or closed-angle, is the gradual and painless loss of VISUAL ACUITY and VISUAL FIELD. Often the pattern of progression begins with loss of peripheral (outside) vision. Over time the field of vision becomes increasingly narrow, which people often describe as “tunnel vision.” Other symptoms of Glaucoma include excessive tearing (especially with close focus tasks such as reading), halos around lights at night, aching eyes, and headaches. Sudden throbbing PAIN in the eye, loss of vision, severe HEADACHE, halos around lights, and a dilated pupil in the affected eye are symptoms of acute closedangle glaucoma.
|Chronic (Open-Angle or Closed-Angle)||Acute Closed-Angle|
|slow loss of peripheral vision||sudden, throbbing PAIN in the EYE|
|“blind spots” in the field of vision||sudden, severe HEADACHE|
|halos around lights at night||sudden restriction or loss of vision|
|teary eyes with close focus tasks||dilated pupil in affected eye|
|achiness in the affected eye||NAUSEA and vomiting|
Though eye care practitioners routinely use TONOMETRY to screen for increased intraocular pressure, this test alone is not sufficient to detect glaucoma. Detecting glaucoma requires a full OPHTHALMIC EXAMINATION including fundus examination to assess the condition of the optic disk. The ophthalmologist will also conduct a visual acuity test and a peripheral vision test. Other procedures that can help diagnose glaucoma in its early stages or quantify the extent of damage in moderate to advanced glaucoma are ULTRASOUND of the eye and OPTICAL COHERENCE TOMOGRAPHY (OCT).
Acute closed-angle requires emergency measures to relieve intraocular fluid and the accumulation of aqueous humor. Such measures typically include a combination of procedures to open the drainage angle, ophthalmic medications to lower intraocular pressure, and systemic medications to draw fluid from cells (osmotics). The ophthalmologist is also likely to administer medications for pain and to minimize NAUSEA and vomiting. Ongoing treatment with glaucoma medications or glaucoma surgery is then necessary. Ophthalmic medications (drops, inserts, and ointments) to open the drainage angle and lower intraocular pressure are the standards of treatment for chronic glaucoma of either form, and typically can control glaucoma for many years.
|Common Glaucoma Medications|
|Type of Drug||Actions|
|alpha-blockers (apraclonidine, brimonidine)—topical ophthalmic preparations||reduce aqueous humor production by slowing function of ciliary processes; increase drainage of aqueous humor|
|beta-blockers (betaxolol, carteolol, levobunolol, metipranolol, timolol)—topical ophthalmic preparations; oral products sometimes used||reduce aqueous humor production by slowing function of the ciliary processes|
|carbonic anhydrase inhibitors (brinzolamide, dorzolamide)—topical ophthalmic preparations||reduce aqueous humor production by blocking the action of the enzyme necessary for its production, carbonic anhydrase|
|miotics (pilocarpine, carbachol)—topical ophthalmic preparations||increase drainage of aqueous humor|
|prostaglandin analogs (latanoprost, travoprost, bimatoprost, unoprostone)—topical ophthalmic preparations||increase drainage of aqueous humor via secondary routes|
Surgery becomes an option to treat glaucoma that becomes advanced or does not respond to medication therapy. Surgical treatments for glaucoma include the following:
Early diagnosis and treatment offer the best opportunity for minimizing vision loss. It is important to diligently follow the directions for using glaucoma medications, as glaucoma requires consistent control. Appropriate treatment can slow the progression of vision loss in most people who have glaucoma.
Age is the most significant risk factor for glaucoma; glaucoma is uncommon in people under age 40 and about two thirds of people who develop glaucoma are over age 65. Glaucoma is more common in people of African American and Asian ethnicity and tends to run in families. Glaucoma also is more likely to develop in people who have hypertension, ATHEROSCLEROSIS, diabetes, and severe MYOPIA (nearsightedness) and in people who take CORTICOSTEROID MEDICATIONS. Prevention focuses on regular ophthalmic examinations to detect glaucoma early in its course.
Resource: Facts On File Encyclopedia Of Health And Medicine
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