Eye Disorders
The eye is the delicate organ of sight with which we keep informed about the natural world around us. Light from an object first strikes the transparent covering of the eyeball, the cornea, then passes through the lens, a clear, flexible disk, which bends the light rays enough so that they focus on the back of the eye, the retina.
Some early discoveries about the physiology of vision were made by Thomas Young, a British physicist and physician. In 1793 he observed that the eye focuses on near or distant objects by changing the shape of the lens. This adjustment is called accommodation. Around the turn of the nineteenth century, Young discovered that color sensation is controlled by tiny structures on the retina which we now call cones, Charles Babbage (1792-1871), an eccentric English mathematician who is sometimes referred to as the grandfather of the modern computer, invented an ophthalmoscope with which to study the retina of the eye in 1847. He gave it to a doctor friend to test, but it was mislaid and forgotten about. Then in 1851 German physician and physicist Hermann von Helmholtz independently invented an ophthalmoscope for which he is usually credited. Helmholtz also invented an ophthalmometer for measuring the curvature of the eye, and he renewed interest and expanded Young's theory about color vision. Each of these theories and inventions enabled physicians to study more closely eye disorders.
The following are fairly common vision problems that do not threaten vision and can often be corrected with corrective lenses--eyeglasses and contact lenses or with surgery. Hyperopia or farsightedness was first explained by Franciscus Donders (1818-1889), a Dutch physiologist who discovered in 1858 that the cause of farsightedness was a too-shallow eyeball that caused the image to focus behind the retina. To correct hyperopia, convex corrective lenses are used. In myopia or nearsightedness, the image is focused in front of the retina so that only near objects can be seen clearly. Concave lenses can be worn to permit focusing for objects far away.
The technique of radial keratotomy involves making incisions on the cornea to correct myopia surgically. It was first done in Japan in 1955 by T. Sato and later in 1979 by Saviatoslav Feodorov in Russia. Whereas radial keratotomy was once considered a risky procedure, in the 1990s the technique has improved. Follow-up interviews on hundreds of patients who underwent the procedure show that two-thirds of the patients were able to stop wearing corrective eyeglasses or contact lenses. A newer, "corneal sculpting" laser surgery that takes only about 30 seconds to complete has been approved to correct myopia. Called photoreactive keratectomy (PRK) the process uses an excimer laser to sculpt a minute area on the surface of the eye. Since the surgery removes only 5-10% of the cornea, the corneal dome's strength and integrity is maintained. This approach has also been used to treat hyperopia and astigmatism. Astigmatism is an eye condition that makes objects appear blurred. Thomas Young suffered from astigmatism and discovered that this condition is due to irregular curves in the cornea. In 1862 Donders found that astigmatism is caused by unevenness in the curvature of either the cornea or lens. The irregular curvature makes it impossible for light rays to focus on a single point. The condition may cause headaches or eye strain. It can be corrected with glasses and certain kinds of contact lenses. Presbyopia occurs when the lens loses it elasticity and it can no longer accommodate. The condition is usually associated with age and becomes evident after 40. Usually presbyopia is corrected by wearing reading glasses. Strabismus is a condition whereby one eye is not able to focus with the other resulting in a deviation toward or away from the nose. Sometimes in children the condition will self correct or surgery is recommended to "uncross " the eyes. Color blindness is the inability to distinguish between certain colors, most often red and green. It is a congenital condition that cannot be cured, but contact lenses to correct color blindness have been invented by Dr. Jay Schlanger.
Blindness is a complete or partial loss of vision. People born with the inability to see have congenital blindness. Other people who lose their vision through accident or disease have acquired blindness. Some of the following eye disorders can lead to blindness if untreated. Cataracts are spots on the lens of the eye which cut off the light that passes through. They are sometimes attributed to age, although they may form in children or persons with diabetes or other conditions. Recent evidence shows that cataracts can be caused by exposure to ultraviolet light. If unchecked, cataracts cause the entire lens to becomes cloudy and blindness results. Glaucoma is a condition in which the eyeball hardens because fluid inside the eye does not drain properly leading to an increase in pressure that can kill the optic nerve and cause blindness. Keratitis is an inflammation of the cornea of the eye. In some cases both the cornea and conjunctiva are inflamed. These two conditions represent a large portion of all eye disease. Keratitis follows cataracts and glaucoma as a leading cause of blindness. The condition has many causes including injury, infection, radiation, irritation by chemicals, or allergy. With the use of contact lenses, especially soft and extended-wear contacts, physicians are seeing an increase in the number of cases of ulcerative keratitis, probably because of a decrease in hygiene associated with wearing lenses around the clock without disinfecting them. Conjunctivitis is a fairly common, very contagious inflammation of the eyelid caused by infection and usually treated with drug therapy. Trachoma is an extremely infectious eye disease which inflames the lining of the eyelid and forms small ulcers on the cornea. It is more prevalent in developing countries than in the United States. Ophthalmia neonatorum affects the eyes of newborns, causing ulcers to form on the cornea, the swelling of eyelids and discharging of pus. It is often caused by gonorrhea passed on from mother to child and is preventable if drops are applied to the infant's eyes. Retinitis is an inflammation of the retina which may be caused by bacterial infection, injury of the eyeball or intense light. Degenerative retinopathy may be brought on by many conditions that change the pressure in the eye including advanced age, diabetes, high blood pressure, arteriosclerosis, anemia, and leukemia. Retinopathy is successfully treated with argon laser surgery. Cytomegalovirus (CMV) retinitis is a frequent eye infection found in AIDS patients and is treated with drug therapy.
The ubiquitous use of the computer, especially in the work environment, has also led to the development of computer vision syndrome (CVS). Recognized as a medical condition by the American Optometric Association, the syndrome affects people who use video display terminals for long periods of time. Although no long-term disability is associated with the condition, which usually abates within hours of leaving the computer, it does cause dry burning eyes, blurred vision, delayed focusing, altered color perception, and headaches.
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