I. INTRODUCTION
Vision gives you a sense of control over your immediate environment. Being able to see the world around you gives you the ability to respond to it appropriately. Vision gives us the ability to interact with our environment and make the appropriate reaction depending on what we perceive or see. (Kandel, Schwartz, Jessell, 2000)
However, there are a number of medical conditions that affect our vision in several ways. As such, it is important to be able to understand how our eyes work and how these conditions affect our sense of sight so that we can take better care of our eyes and avoid vision problems, be able to take the necessary medical steps in order to save our vision, or learn to accept and live with blindness if such is the case.
This paper will zero in on one particular vision problem which is glaucoma in the hopes that those who read this paper will able to gain some useful information in the mechanism, prevention, and treatment of said disease.
II. THE HUMAN EYE
Before any vision problems can be discussed, it is important to have a basic understanding of how our eyes work.
Professor David Ball in his The Basics of Spectroscopy article defines the eye as a light-reactive organ of vision in animals. It is so sensitive that it can distinguish minute variations of shape, color, brightness, and distance. The actual process of seeing is performed by the brain. The main function of the eye is to capture light and translate it into patterns of nerve impulses that can be interpreted by the brain. (2005)
The human eye is a spheroid structure protected by a bony cavity on the front of the skull. The eyeball is surrounded by three structural layers: the sclera, the choroid, and the retina. The sclera is the outermost layer of eye tissue; it is visible as the “white” of the eye. In the center of the visible sclera and projecting slightly, is the cornea, a transparent membrane that acts as the window of the eye. A delicate membrane, the conjunctiva, covers the visible portion of the sclera. (Columbia Encyclopedia, 2004, p.16297)
The iris is the coloration of the eye. The pupil is the round opening in the center of the iris; the pupil can dilate and contract, thus regulating the amount of light that enters the eye. Behind the iris is the lens, a transparent, elastic structure that focuses the light on the retina where the signals are ultimately interpreted and “seen”. (Cassin, Solomon, 1990)
Right: The amount of light entering the eye is controlled by the pupil, which dilates and contracts accordingly. The cornea and lens, whose shape is adjusted by the ciliary body, focus the light on the retina, where receptors convert it into nerve signals that pass to the brain. A mesh of blood vessels, the choroid, supplies the retina with oxygen and sugar.
Left: Lacrimal glands secrete tears that wash foreign bodies out of the eye and keep the cornea from drying out. Blinking compresses and releases the lacrimal sac, creating a suction that pulls excess moisture from the eye’s surface.© Microsoft Corporation. All Rights Reserved.
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Eye movement is controlled by six muscles that are directly attached to the eyeball. The four rectus muscles form a relatively straight line from their points of origin, while the two oblique muscles approach the surface of the eye at an angle. All the muscles combine to keep the eyeball in nearly constant motion in order to maximize human vision, which is capable of focusing on about 100,000 distinct points in the visual field. These muscles also enable both eyes to focus on the same point simultaneously, thereby creating effective depth perception.© Microsoft Corporation. All Rights Reserved.
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III. GLAUCOMA
Theodore Duncan said that the eye is no more immune to aging than other parts of the body. (1982, p. 273). In fact, vision problems are one of the first complications of growing older, and fewer and fewer of us can do without some aid to vision like glasses and contact lenses.
The term ‘glaucoma’ refers to a large number of diseases that can damage the eye’s optic nerve and result in vision loss and blindness. Glaucoma occurs when the normal fluid pressure inside the eyes slowly rises. Glaucoma is associated with a gradual loss of the visual field, which can lead to total, irreversible blindness if the disorder is not diagnosed and treated properly. (Blanco, Costa, Wilson, 2002, p.17)
The visual field as referred to in glaucoma is defined as the portion of space in which objects can be seen in the periphery while the eye is looking in one fixed direction or object. Vision field is also referred to as peripheral. (Blanco, Costa, Wilson, 2002, p.67)
Normal vision Same scene as viewed by a person with glaucoma
http://www.nei.nih.gov/health/glaucoma/glaucoma_facts.asp
A. PATHOLOGY
The disease is associated with the narrowing of the vision or what we commonly refer to as tunnel vision. Because the vision arc decreases, the eye can only see what is in front of it. This disease marked in most cases by a blockage of the fluid, the aqueous humor that normally drains from the front part of the eye. James Zeitlin describes the mechanism of glaucoma… “Trapped but constantly replenished by the gland that produces it, the welling fluid builds up pressure against the shell of the eyeball and particularly the optic nerve, causing compression of the nerve cells and their death and, eventually, permanent loss of some vision, particularly in the periphery.” (2001, p.1)
B. PREVALENCE
Glaucoma needlessly blinds 80,000 Americans each year. (Ackerman, 1995, p. 17) The illness is called “the sneak thief of sight,” and it strikes African-Americans at a higher rate than any other race. In fact, I in every 13 Blacks have glaucoma. (Glaucoma: The Sneak Thief of Sight, 2003, p.84)
C. TREATMENT AND PROGNOSIS
At present, there is no known cure for glaucoma. However, early intervention measures can prevent further vision loss. Because glaucoma is a degenerative disease, the best that we can do is slow down its progression. When you have the facts, you can take charge of your health with just a few adjustments to your routine. The appropriate treatment depends upon the type of glaucoma and the associated medical condition of the patient. With the proper combination of procedures and medications, most cases of glaucoma are manageable. (http://www.glaucoma.org/living/)
Among the most common procedures for glaucoma is laser surgery. Laser has particularly been effective in treating a number of eye problems; and has allowed people to regain their clear eyesight and be free from corrective glasses.
As far as medications are concerned, they are usually in the form of eye drops so that the action is localized directly on the eye. There are several types of medications, with each having a different action, depending on the type of glaucoma you have; however, most of them are given to decrease intraocular pressure. With glaucoma medications, strict compliance and regular check-ups are necessary. (Duncan, 1982, p. 273)
Of course, as with any disease, vigilance and early detection is vital to stopping the progress of glaucoma. Patient education and constant communication with your doctor is crucial is management plans are to be successful plans. If you are fortunate to have detected the disease and exhibit no early symptoms, then intervention procedures will have a better chance of preventing any loss of vision.
D. TYPES OF GLAUCOMA
The most common types of glaucoma are the following:
1. Primary Open Angle Glaucoma (POAG) – Improper drainage of the eyes causes fluid build-up which elevates the pressure in the eye. The term open angle is used because the chamber where fluids exit the eye is normal and not constricted. The cause of drainage may be due to other factors.
2. Pseudoexfoliative Glaucoma (PEX): White, fibrous deposits block the eye’s drainage system, causing high intraocular pressure and damage to the optic nerve characteristic of POAG. These deposits do not always cause glaucoma, and their direct cause is still not clear to science.
3. Primary Angle-Closure Glaucoma (PACG): This glaucoma is primarily due to a structural problem. The angle where the fluid drains is acute, causing blockages and the fluid build-up which causes the high internal eye pressure. Medications that dilate the eye’s pupil also can cause angle-closure glaucoma.
4. Pigmentary Glaucoma: Pigmented cells from the iris are deposited along eye structures. These deposited cells then obstruct the eye’s drainage system, which can lead to buildup of internal eye pressure and glaucoma. Inability to focus on distant objects (nearsightedness) is considered a risk factor for developing pigmentary glaucoma.
5. Normal Tension Glaucoma (NTG): This is the only type of glaucoma where is no elevation of internal eye pressure. As such, vision loss tends to occur centrally rather than along the periphery. Not much is known about NTG, except that genetics appear to play a major part in their occurrence. NTG is also strongly associated with conditions such as migraines, which might indicate a relationship to blood circulation (vascular) abnormalities (http://vision.about.com/od/glaucoma/a/whatisglaucoma_2.htm.).
E. SYMPTOMS AND DETECTION
At the onset of glaucoma, there are no symptoms. Initially vision is normal, and there is no pain in the eye. As glaucoma progresses, the person may notice some problems with vision, particularly in the periphery. That means that objects directly in front of the eyes are still clear, but those on the side are blurred.
If the disease is untreated, people will progressively lose their vision, starting from the side, going center. Without intervention or management procedures, this loss of vision will progress until blindness.
F. RISK FACTORS
To be able to watch out for glaucoma, one must know the risk factors that increase the likelihood of the disease. The following are some of the risk factors as taken from http://www.glaucomafoundation.org/education_content.php?i=12:
· People over the age of 45.
· People who have a family history of glaucoma.
· People with abnormally high intraocular pressure (IOP).
· People of African descent.
· People who have:
Ø Diabetes
Ø Myopia (nearsightedness)
Ø Regular, long-term Steroid/Cortisone use
Ø A previous eye injury
IV. CONCLUSION
The main structure involved in glaucoma is the optic nerve. Damage to the optic nerve is secondary to elevated intraocular pressure. This high pressure causes undue stress to the nerve which causes it to malfunction. The high intraocular pressure is brought about by many things, but is primarily due to fluid build up.
Glaucoma is a progressive disease, which if left unattended to can lead to total loss of vision or blindness. While we have no way of stopping it in its tracks, with early detection and proper adherence to prescribed treatments, glaucoma is a very manageable and the accompanying vision loss can be delayed indefinitely. Indeed science has made tremendous inroads in helping people with glaucoma lead healthy, productive lives, while keeping their visions intact for as long as possible.
References:
Ackerman SJ, (1982). Guarding against Glaucoma. FDA Consumer. Volume: 29.
Issue: 9. U.S. Government Printing Office. p. 17.
Azuara-Blanco A., Costa V., & Wilson R. (2002). Handbook of Glaucoma. London.
pp.17, 67.
Ball, DW, (2005). The Basics of Spectroscopy.
Cassin, B., & Solomon S., (1990). Dictionary of Eye Terminology. Florida. Triad
Publishing Company.
Cline D., Hofstetter HW, & Griffin JR,. (1997). (4th ed.). Dictionary of Visual Science.
Boston. Butterworth-Heinemann.
Duncan, T.,(1982), Over 55: A Handbook on Health. Franklin Institute Press.
Philadelphia. p. 273.
Kandel ER, Schwartz JH, & Jessell TM. (2000). (4th ed.). Principles of Neural Science.
New York. McGraw-Hill.
Zeitlin, J., (2001). Glaucoma Causes Many Cloudy Days.Newspaper Title: The
Washington Times. p.1.
Glaucoma ‘The Sneak Thief of Sight’. (2003). Glaucoma Foundation Leads Campaign
against Eye Disease. Magazine Title: Ebony. Volume: 58. Issue: 9. Johnson
Publishing Co. p. 84.
Microsoft Encarta. (Premium Suite). (2005).
The Columbia Encyclopedia. (6th ed.) (2004). New York. Columbia University Press.
Licensed from Lernout & Hauspie Speech Products N.V.
http://www.glaucoma.org/living/
http://www.nei.nih.gov/health/glaucoma/glaucoma_facts.asp
http://nihseniorhealth.gov/glaucoma/glaucomadefined/glauc_m_popup.html
http://vision.about.com/od/glaucoma/a/whatisglaucoma_2.htm