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 Mosby’s 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. illion 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 which the aqueous humor flows out of the eye; there is also an age-related reduction in the size of the Schlemm’s canal (Harmon & Intrator, 2004).
A study on family history of glaucoma in the primary and secondary open-angle glaucomas (Budde & Jonas, 1998) contends that family history of glaucoma is considered to be a risk factor for the development of the disease. First-degree relatives of people with POAG have an eight-fold increased risk of developing the disease. Overall risk factors for developing glaucoma increase with the number and strength of the risk factors. Other risk factors in the development of glaucoma include systemic hypertension, cardiovascular disease, myopia, migraine headache, peripheral vasospasm, and obesity.
Seddon et al. (1983) found that patients with systemic hypertension were two to three times more likely to have an increased ocular pressure than normotensive patients. POAG has been noted to have a higher prevalence rate among people with Type II diabetes; diabetics are more susceptible to glaucomatous field loss and have a larger than average cup-to-disc ratio, thus a higher IOP than non-diabetics. Landmark Studies The most common form of glaucoma in the United States is primary open angle glaucoma (POAG). There are no signs to indicate the rise in pressure.
Without symptoms, a person with a rise in their IOP does not know until their vision is permanently affected. The glaucoma clinical trials were developed and performed to help physicians better manage glaucoma. These studies have provided valuable lessons about glaucoma that can help physicians make treatment decisions. The three clinical trials were: Ocular Hypertension Treatment Study, Collaborative Initial Glaucoma Treatment Study, and Early Manifest Glaucoma Trial. The question to ask is what lessons were learned from these three particular studies?
The answer lies with lowering the IOP. The Ocular Hypertension Treatment Study evaluated whether “lowering IOP was effective in delaying or preventing glaucoma in patients with ocular hypertension” (Johnson & Brandt, 2005). This study was designed to identify the characteristics in progression of disease in patients. Also identified as major predictive factors for development of glaucoma was optic nerve anatomy and central corneal thickness (CCT). Study results concluded “only 4. 4% of OHT study participants who received treatment developed glaucoma within five years.
In comparison, 9. 5% of individuals who were not medicated went on to develop glaucoma within five years” (Harmon & Intrator, 2004). The participants without treatment developed glaucoma at more than twice the rate of the treated group. Treatment is introduced earlier in these individuals than before this study. An interesting fact is that this study was really the first well-conceived attempt to introduce the concept of risk assessment and analysis. The OHTS trial confirms the importance of IOP control in the treatment of glaucoma.
The Collaborative Initial Glaucoma Treatment Study (CIGTS) measured whether medication or filtration surgery was better for the treatment of POAG (Johnson & Brandt, 2005). Patients have reported a decline in symptoms over time, but the surgery group experienced more foreign body sensation and ptosis which is defined as “drooping of one or both upper eyelids; it may be congenital or result from damage to the oculomotor nerve, myasthenia gravis, or other disorder” (Rothenberg, 2000). CIGTS is an important study.
It confirmed that no matter how the IOP was lowered in patients with newly diagnosed primary open angle glaucoma, physicians could stabilize the visual field and stop progression. The Early Manifest Glaucoma Trial was “conceived before the role of IOP reduction in delaying or preventing glaucomatous visual field loss was well established” (Johnson & Brandt, 2005). The evaluated efforts of immediate treatment or no treatment on early-stage open angle glaucoma was tested. The progression rates for glaucoma seen in this study are higher than other studies.
This could be explained that progression was defined very sensitively, so that any subtle change in the visual field was considered to be from progression. The highlights from glaucoma clinical trials are in lowering intraocular pressure (IOP) that may delay or prevent glaucoma, medication or surgery as initial treatment as an effective way to long term IOP lowering, and in treating glaucoma early may lower the risk of progression of disease. Today physicians are searching for scientific evidence with regard to whom to treat, when to treat, and how aggressively to treat.
These decisions about glaucoma therapy can be based on the results of these and many other clinical trials. Prevalence and Incidence of Glaucoma in the United States Studies have shown that glaucoma is the second leading cause of blindness in the United States (Leske, 1983) as well as the second leading cause of bilateral blindness in the world (Quigley, 1996). According to Healthy People 2010, glaucoma is a major public health problem in this country. An estimated 3 million people in the United States have the disease; (Rahmani et al, 1996) of these, as many as 120,000 are blind as a result (Kahn & Moorehead, 1973).
Furthermore, glaucoma is the number one cause of blindness in African Americans. However, at least half of the people who have glaucoma are not receiving treatment because they are unaware of their condition. Blindness from glaucoma is believed to impose significant costs annually on the Federal Government in Social Security benefits, lost tax revenues, and health care expenditures (Healthy People 2010). Healthy People 2010 also stated that, more than two-thirds of visually impaired adults are over age 65 years.
Although no gender differences exist in the number of older adults with vision problems, more women are visually impaired than men are because, on average, women live longer than men do. By 1999, almost 34 million persons in the United States were expected to be over age 65 years; that number is expected to more than double by the year 2030 (U. S. Bureau of the Census, 1999). As the population of older adults grows larger, the number of people with visual impairment and other aging-related disabilities is expected to increase.
Anyone can develop glaucoma. Some people are at higher risk than others. They include: African Americans over age 40, everyone over age 60, especially Mexican Americans, and people with a family history of glaucoma. A comprehensive dilated eye exam can reveal more risk factors, such as high eye pressure, thinness of the cornea, and abnormal optic nerve anatomy. In some people with certain combinations of these high-risk factors, medicines in the form of eye drops reduce the risk of developing glaucoma by about half (National Eye Institute, 2004).
African Americans are twice as likely to be visually impaired as are Whites of comparable socioeconomic status. Studies conducted in the United States and the West Indies have shown that primary open-angle glaucoma exists in a substantially higher proportion of Caribbean Blacks and African Americans than in Whites (Klein et al. , 1992); (Leske et al. , 1983). Hispanics have three times the risk of developing Type II diabetes as Whites, and they also have a higher risk of complications (Novella, Wise, and Kleinman, 1991).
This is significant since diabetes may be a risk factor for glaucoma. Many barriers still need to be overcome in reducing vision disorders. Among the major prevention strategies are educating health care professionals and the general population about the benefits of prevention, improving access to quality health care across socioeconomic classes to decrease disparities, and gaining cooperation of families in the screening and treatment of infants and children (Healthy People 2010).