Eye Disorders: Overview

Eye disorders include cataracts, glaucoma, iritis, retinal disorders, macular degeneration, pink eye or conjunctivitis, and dry eye. Disorders of the eye can cause temporary or permanent damage to or loss of vision.

Common disorders or diseases of the eye include refractive errors, cataracts, glaucoma, iritis, retinal disorders, macular degeneration, conjunctivitis, dry eye, and color blindness.

Refractive errors are errors in the eye's ability to focus light on the retina, the layer of light-sensitive tissue at the back of the eye. They include farsightedness (hyperopia); nearsightedness (myopia); the inability to focus on close work (presbyopia); and focus problems caused by irregularities in the curvature of the cornea or the lens (astigmatism). Such refractive errors as farsightedness and nearsightedness may develop during childhood or may be present at birth. Presbyopia is a result of the aging process, so older adults are at greatest risk of presbyopia. The word presbyopia comes from a Greek word that means older adult.

Cataracts are a clouding of the lens of the eye and are often the result of aging. Cataracts can also be caused by prolonged exposure to sunlight. Older adults are at greatest risk of developing cataracts.

Glaucoma is a group of diseases that damage the optic nerve. The optic nerve is the major component of the brain responsible for vision. There are several types of glaucoma: open-angle glaucoma, closed-angle glaucoma, secondary glaucoma, and congenital glaucoma. Secondary glaucoma is usually related to an injury to the eye; an inflammation of the eye; abnormal blood vessel formation (usually seen in diabetes); and the use of steroid-containing medications. Most types of glaucoma affect the drainage system of the eye. Glaucoma is the leading cause of blindness in the United States.

Iritis, also called anterior uveitis, is an inflammation of the iris (the colored part of the eye). The iris is part of the middle layer of the eye, which is called the uvea. The usual causes of iritis are infection (often from herpes simplex, herpes zoster, and Lyme disease); injury or trauma to the eye (including burns); genetic predisposition; and a complication of some medications, including antiviral medications. The genetic predisposition to iritis seems to be related to autoimmune diseases, in that people with some autoimmune diseases like ankylosing spondylitis and rheumatoid arthritis are likely to develop iritis or uveitis.

Retinal disorders include detached retina, macular degeneration, diabetic eye diseases, and retinoblastoma (cancer of the eye). The retina is the light-sensitive lining at the back of the eye that contains the blood and nerve supply as well as the macula * , which facilitates high-resolution focusing on objects. Causes of detached retina include injury to the eye and such diseases that cause retinopathy (disease of the retina) as diabetes or sickle cell anemia.

Macular degeneration, or age-related macular degeneration (AMD), is a progressive degenerative disease of the macula that destroys sharp central vision. The macula is a small ovalshaped area located on the back of the eye near the eye center of the retina. Images are formed on the macula and transmitted to the brain for interpretation. There are two types of macular degeneration: dry and wet.

Macular degeneration is most likely to occur in adults older than 55 years of age. Genetic factors are thought to play a major role in AMD. There is a greater risk of AMD in families in which another family member has AMD. Other risk factors for AMD include a high-cholesterol diet, obesity, cigarette smoking, exposure to bright sunlight, cardiovascular disease, and hypertension.

Dry eye is the name of the condition in which there are insufficient tears to cleanse and protect the eye. There may be inadequate tear production, poor consistency of the tears produced, or increased evaporation of tears. Other names for dry eye include dry eye syndrome, dysfunctional tear syndrome, and evaporative tear deficiency. Dry eye can be associated with (1) diseases of the skin on or around the eye; (2) diseases of the eyelid; (3) side effects of medications taken for other conditions; (4) allergies; and (5) infrequent blinking that develops when a person stares at a video or computer screen for long periods of time.

People at increased risk of dry eye include women taking hormone replacement therapy; pregnant women; people who wear contact lenses for long periods of time, and the elderly. People who have such autoimmune disorders as rheumatoid arthritis, systemic lupus erythematosus, and Sjδgren's syndrome are at increased risk of dry eye. People who work in occupations that require constant computer use are also at increased risk of dry eye.

Color blindness is the inability or decreased ability to see color, or to perceive differences in color under normal lighting. It is important to note that color blindness is not actual blindness, but rather the inability to distinguish between colors or various shades of a color. Color blindness is also called color vision deficiency, or color vision defect.

The cone cells or photoreceptor cells, which are responsible for color vision, are located in the retina of the eye. There are three types of color blindness associated with defects in the photopigments of the three different types of cone cells: red-green, blue-green, or total absence of color vision. Red-green color blindness is the most common; total color blindness is rare. Color blindness is primarily a sex-linked inherited disorder, as the genes responsible for inherited color blindness are located on the X chromosome and produce the disorder more often in males than in females. Inherited color blindness may be present at birth, begin in childhood, or not appear until adult life. Color blindness can also be caused by physical or chemical damage to the eye, the optic nerve, or the parts of the brain that process color information. Color vision also declines with age, usually associated with the development of cataracts.

Although a detached retina can happen at any age, retinal detachment is more common in people older than 40 years of age, more common in men than in women, and more common in Caucasians than in African Americans. Retinal detachment is more likely to occur in people who have a family history of retinal detachment; are extremely nearsighted; have already had a detached retina in one eye; have had cataract surgery or an eye injury; or have such other diseases of the eye as lattice retinal degeneration.

AMD is the most common cause of blindness in older adults. The dry type of AMD accounts for approximately 90 percent of all cases. According to the Foundation Fighting Blindness, approximately 10 million people in the United States either have AMD or are at risk of developing it. Pink eye is one of the most common disorders of the eye in children and adults, accounting for 30 percent of eye-related complaints. Dry eyes is a common problem that affects more than 10 million people in the United States each year.

The following list indicates how and when people know they have either refractive errors, cataracts, glaucoma, iritis, retinal disorders, macular degeneration, conjunctivitis, dry eye, or color blindness.

Healthcare providers take a complete health history from patients and ask specific questions about vision and such related symptoms as headaches, and diseases that may affect vision, including diabetes. A complete eye and vision examination is conducted. Often people with eye or vision problems are referred to a specialist called an ophthalmologist * , who can perform a more thorough examination of the external and internal eye using specialized equipment. One instrument used to examine the eye is an ophthalmoscope * .

The following list indicates how refractive errors, cataracts, glaucoma, iritis, retinal disorders, macular degeneration, conjunctivitis, dry eye, and color blindness are treated.

Most refractive errors cannot be prevented. Cataracts are related primarily to aging and thus cannot be prevented. Because sun exposure can increase the risk of developing cataracts, people should wear protective sunglasses when exposed to the sun. Wearing a hat with a wide brim also provides some eye protection by keeping the eyes within the shadow of the hat brim. Glaucoma cannot be prevented, but early diagnosis and treatment can preserve vision and delay loss of vision.

Because iritis can be caused by infection, people should take care to avoid touching their eyes, and they should wash their hands thoroughly if they must touch their eyes. Taking precautions to prevent such injuries as burns and trauma to the eyes by wearing protective goggles when working with equipment or chemicals also prevents iritis. If iritis is related to a particular medication, discontinuing or changing the medication can prevent or relieve iritis.

In general, retinal detachment cannot be prevented. Wearing protective eyewear or goggles when participating in sports or working with tools or other equipment that may cause eye injuries is important. Getting immediate treatment for a detached retina can prevent permanent loss of vision. People who are at risk of retinal detachment should have a yearly eye exam.

The genetic risk of AMD cannot be prevented. A person can, however, control other risk factors such as diet, weight, cigarette smoking, and sun exposure. Wearing a sun hat and protective eyewear like sunglasses whenever going outside can decrease the risk associated with sun exposure.

Some strategies that can prevent pink eye include avoidance of touching the eyes and the surrounding tissues; thorough handwashing before touching the eyes and the surrounding tissues; avoidance of sharing eye makeup; and use of disposable applicators to apply eye makeup (discarding the applicators after each use).

The use of over-the-counter artificial tears can help relieve dry eye. Wearing wraparound glasses or sunglasses can decrease dry eye related to evaporation. It is helpful to rest and blink the eyes intermittently to moisten the surface of the eye when working or playing on a computer, or when watching television, reading, or doing such close work as needlepoint.

Color blindness cannot be prevented. It is a genetic disorder. Recognizing color blindness early is important so that appropriate strategies can be taken to prevent learning difficulties in children and to help adults cope with color blindness in daily life. For example, a person who is colorblind will have difficulty reading traffic lights by color. They must learn to read traffic lights by the position of the light; that is, that the green light is on the bottom of most traffic lights and the red light is on the top.

See also Aging • Allergies • Astigmatism • Autoimmune Disorders: Overview • Blindness • Cataracts • Color Blindness • Detached Retina • Diabetes • Eyelid Disorders: Overview • Farsightedness • Glaucoma • Nearsightedness • Pink Eye (Conjunctivitis) • Sjögren's Syndrome

* macula (mack-u-la) is a small oval-shaped area on the retina that contains the fovea centralis, which is responsible for central vision.

* allergen is a substance that provokes a response by the body's immune system or causes a hypersensitive reaction. Also called an antigen.

* antihistamine (an-ti-hiss-tahmeen) is a drug that opposes the action of histamine and is often used to treat allergic reactions.

* over-the-counter are medications and other treatments that can be purchased without a doctor's prescription or order.

* artificial tears are eye drops used to lubricate or provide moisture for the eyes.