Glaucoma In The Us
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Abstract
This research paper examines glaucoma over the age of 40 in the United States, in the last 10 years. Knowing the fact that glaucoma is the second leading cause of blindness in the United States leads us to choose this subject for research. Glaucoma is a group of eye diseases that gradually steals sight without warning and often without symptoms. Vision loss is caused by damage to the optic nerve. This nerve acts like an electric cable with over a million wires and is responsible for carrying the images we see to the brain. The two main types of glaucoma are open angle glaucoma, or primary open angle glaucoma (POAG), and angle closure glaucoma. Currently, there is no cure for glaucoma. Glaucoma is a chronic disease that must be treated for life. However, much is happening in research that makes us hopeful a cure may be realized in our lifetime. There is exciting work being conducted by scientists all over the world in the areas of genetics, neuroprotection and neuroregeneration. These areas of study deal with the origins and pathology of glaucoma as opposed to managing symptoms. A cure is on the way.
Glaucoma over the Age of Forty in the United States
The term “glaucoma” encompasses a group of eye diseases, not a single entity. Glaucoma is described broadly in terms of aqueous fluid drainage through the trabecular meshwork, the major outflow pathway. There are two main types: angle closure glaucoma and open angle glaucoma. Open angle glaucoma is far more common in the United States.
The American Academy of Ophthalmology defines primary angle closure glaucoma as “An appositional or synechial closure of the anterior chamber angle caused by relative pupillary block in the absence of other causes of angle closure”. The American Academy of Ophthalmology defines primary open angle glaucoma as a “Multifactorial optic neuropathy in which there is a characteristic acquired loss of optic nerve fibers”. Classifying glaucoma broadly into angle closure glaucoma or open angle glaucoma is helpful from both a diagnostic and pathophysiological perspective.
Problem Statement
In the United States, approximately 2.2 million people age 40 and older have glaucoma, and of these, as many as 120,000 are blind due to the disease. The number of Americans with glaucoma is estimated to increase to 3.3 million by the year 2020. Each year, there are more than 300,000 new cases of glaucoma and approximately 5,400 people suffer complete blindness. Glaucoma is a leading cause of blindness among African Americans and Hispanics in the United States. African Americans experience glaucoma at a rate of three times that of Whites and experience blindness six times more frequently. Between the ages of 40 and 64, glaucoma is fifteen times more likely to cause blindness in African Americans than in Whites.
Vision experts estimate that half of those affected may not know they have glaucoma because symptoms may not occur during the early stages of the disease. By the time the patient notices something is wrong, the disease has already caused considerable damage. Unfortunately, the vision lost to glaucoma is gone forever. Medications and surgery can help slow the progression of the disease, but there is no cure.
Importance of the Study
The fact that glaucoma is the second leading cause of blindness in the United States renders this study as extremely important. There is no known treatment for glaucoma, so every little bit of information we can obtain is very important.
Natural History of Glaucoma
Mosbys dictionary (Anderson, 1998) defines glaucoma as “an abnormal condition of elevated pressure within the eye caused by obstruction of the outflow of aqueous humor”. Several types of glaucoma have been identified; however, the most common are Primary Open Angle Glaucoma (POAG), which has a slow insidious onset, and Angle Closure Glaucoma (ACG), which is less common and more acute in nature (World Health Organization, 2005).
It is noted that POAG is a significant public health problem. POAG is an important cause of blindness and more frequently found to cause nonreversible blindness in African Americans (American Academy of Ophthalmology, 2004). POAG is manageable and because the visual impairment caused by glaucoma is irreversible, early detection is essential. In the United States more than seven million office visits are made per year to monitor those who have glaucoma or are at risk of developing the disease. Blindness from glaucoma is estimated to cost in excess of $1.5 billion per year (Weinreb, 2004).
Causality Assessment
POAG is a chronic, bilateral disease that is characterized by progressive damage of the optic nerve shown by changes in the optic disc, retinal fiber layer or visual field; with an adult onset (Weinreb, 2004). POAG typically has a gradual rise in intraocular pressure (IOP); there is no apparent cause or initiating event, and there is no outward sign the IOP elevation is occurring. There is no pain, no blurred vision, and the cornea does not swell. The main reason this disease goes undetected is because it presents with no symptoms. Peripheral vision is affected first; as the disease progresses central vision is affected (Harmon & Intrator, 2004).
IOP is regulated by a balance between the secretion and drainage of aqueous humor. Aqueous humor provides nutrients to the iris, lens, and cornea; it exits the eye into the venous circulation. The optic nerve contains about one million nerve fibers, which converge on the optic disc to form the optic nerve. The optic disc is 1.5 mm in diameter and vertically oval. Axons of retinal ganglion cells make up the retinal nerve fiber layer which is the innermost layer of the retina; these axons converge to form a depression in the optic disk known as the cup. With glaucoma the width of the neuro-retinal rim decreases therefore enlarging the optic disk cup resulting in neuronal death (Weinreb, 2004).
The level of IOP is related to the death of retinal ganglion cells and optic nerve fibers of patients with POAG. When pressure increases above physiological levels, the pressure gradient across the lamina cribosa also increases. In glaucoma, cupping of the optic disc and compression, stretching, and remodeling of the lamina cribosa arises in response to the increased intraocular pressure (Weinreb, 2004).
POAG is present in approximately 2% of the population worldwide over forty years old. The incidence of the disease increases with age due to the narrowing of the spaces through