Common Eye Disorders
Approximately 11 million Americans aged 12 years and older could improve their vision through proper refractive correction. More than 3.3 million Americans aged 40 years and older are either legally blind (having best-corrected visual acuity of 6/60 or worse (=20/200) in the better-seeing eye) or are with low vision (having best-corrected visual acuity less than 6/12 (<20/40) in the better-seeing eye, excluding those who were categorized as being blind). The leading causes of blindness and low vision in the United States are primarily age-related eye diseases such as age-related macular degeneration, cataract, diabetic retinopathy, and glaucoma. Other common eye disorders include amblyopia and strabismus.
For a basic demonstration of the eye’s anatomy, watch the Anatomy videoExternal.
Refractive errors are the most frequent eye problems in the United States. Refractive errors include myopia (near-sightedness), hyperopia (farsightedness), astigmatism (distorted vision at all distances), and presbyopia that occurs between age 40–50 years (loss of the ability to focus up close, inability to read letters of the phone book, need to hold newspaper farther away to see clearly) can be corrected by eyeglasses, contact lenses, or in some cases surgery. Recent studies conducted by the National Eye Institute showed that proper refractive correction could improve vision among 11 million Americans aged 12 years and older.
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Age-Related Macular Degeneration
Macular degeneration, often called age-related macular degeneration (AMD), is an eye disorder associated with aging and results in damaging sharp and central vision. Central vision is needed for seeing objects clearly and for common daily tasks such as reading and driving. AMD affects the macula, the central part the retina that allows the eye to see fine details. There are two forms of AMD—wet and dry.
Wet AMD is when abnormal blood vessel behind the retina start to grow under the macula, ultimately leading to blood and fluid leakage. Bleeding, leaking, and scarring from these blood vessels cause damage and lead to rapid central vision loss. An early symptom of wet AMD is that straight lines appear wavy.
Dry AMD is when the macula thins overtime as part of aging process, gradually blurring central vision. The dry form is more common and accounts for 70–90% of cases of AMD and it progresses more slowly than the wet form. Over time, as less of the macula functions, central vision is gradually lost in the affected eye. Dry AMD generally affects both eyes. One of the most common early signs of dry AMD is drusen.
Drusen are tiny yellow or white deposits under the retina. They often are found in people aged 60 years and older. The presence of small drusen is normal and does not cause vision loss. However, the presence of large and more numerous drusen raises the risk of developing advanced dry AMD or wet AMD.
It is estimated that 1.8 million Americans aged 40 years and older are affected by AMD and an additional 7.3 million with large drusen are at substantial risk of developing AMD. The number of people with AMD is estimated to reach 2.95 million in 2020. AMD is the leading cause of permanent impairment of reading and fine or close-up vision among people aged 65 years and older.
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Cataract is a clouding of the eye’s lens and is the leading cause of blindness worldwide, and the leading cause of vision loss in the United States. Cataracts can occur at any age because of a variety of causes, and can be present at birth. Although treatment for the removal of cataract is widely available, access barriers such as insurance coverage, treatment costs, patient choice, or lack of awareness prevent many people from receiving the proper treatment.
An estimated 20.5 million (17.2%) Americans aged 40 years and older have cataract in one or both eyes, and 6.1 million (5.1%) have had their lens removed operatively. The total number of people who have cataracts is estimated to increase to 30.1 million by 2020.
Diabetic retinopathy (DR) is a common complication of diabetes. It is the leading cause of blindness in American adults. It is characterized by progressive damage to the blood vessels of the retina, the light-sensitive tissue at the back of the eye that is necessary for good vision. DR progresses through four stages, mild nonproliferative retinopathy (microaneurysms), moderate nonproliferative retinopathy (blockage in some retinal vessels), severe nonproliferative retinopathy (more vessels are blocked leading to deprived retina from blood supply leading to growing new blood vessels), and proliferative retinopathy (most advanced stage). Diabetic retinopathy usually affects both eyes.
The risks of DR are reduced through disease management that includes good control of blood sugar, blood pressure, and lipid abnormalities. Early diagnosis of DR and timely treatment reduce the risk of vision loss; however, as many as 50% of patients are not getting their eyes examined or are diagnosed too late for treatment to be effective.
It is the leading cause of blindness among U.S. working-aged adults aged 20–74 years. An estimated 4.1 million and 899,000 Americans are affected by retinopathy and vision-threatening retinopathy, respectively.
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Glaucoma is a group 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. However, recent findings now show that glaucoma can occur with normal eye pressure. With early treatment, you can often protect your eyes against serious vision loss.
There are two major categories “open angle” and “closed angle” glaucoma. Open angle, is a chronic condition that progress slowly over long period of time without the person noticing vision loss until the disease is very advanced, that is why it is called “sneak thief of sight.” Angle closure can appear suddenly and is painful. Visual loss can progress quickly; however, the pain and discomfort lead patients to seek medical attention before permanent damage occurs.
Amblyopia, also referred to as “lazy eye,” is the most common cause of vision impairment in children. Amblyopia is the medical term used when the vision in one of the eyes is reduced because the eye and the brain are not working together properly. The eye itself looks normal, but it is not being used normally because the brain is favoring the other eye. Conditions leading to amblyopia include strabismus, an imbalance in the positioning of the two eyes; more nearsighted, farsighted, or astigmatic in one eye than the other eye, and rarely other eye conditions such as cataract.
Unless it is successfully treated in early childhood amblyopia usually persists into adulthood, and is the most common cause of permanent one-eye vision impairment among children and young and middle-aged adults. An estimated 2%–3% of the population suffer from amblyopia.
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Strabismus involves an imbalance in the positioning of the two eyes. Strabismus can cause the eyes to cross in (esotropia) or turn out (exotropia). Strabismus is caused by a lack of coordination between the eyes. As a result, the eyes look in different directions and do not focus simultaneously on a single point. In most cases of strabismus in children, the cause is unknown. In more than half of these cases, the problem is present at or shortly after birth (congenital strabismus). When the two eyes fail to focus on the same image, there is reduced or absent depth perception and the brain may learn to ignore the input from one eye, causing permanent vision loss in that eye (one type of amblyopia).
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An inherited disorder present at birth or early in life, Usher’s Syndrome involves hearing loss and a progressive loss of vision caused by retinitis pigmentosa (discussed above). The hearing loss associated with this disorder, which may be from mild to profound, usually does not progress. The retinitis pigmentosa, however, follows the usual pattern of progressive loss first of night vision and gradually of peripheral vision. The incidence of Usher’s Syndrome is estimated by the RP Foundation at about 1 in 15,000 to 30,000 births. There is no treatment for this disorder, but there has been some benefit from cochlear implants for those with severe hearing loss.
Inflammation of the uvea, the middle layer of the eye between the sclera and the retina, is called uveitis. Symptoms include light sensitivity, blurring of vision, pain, and redness of the eye. This condition can affect other parts of the eyeþcornea, retina, sclera, for example and may be serious enough to lead to loss of vision. It may come on slowly with little pain but with blurring of vision, or it may appear suddenly, accompanied by pain and redness of the eye.
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What Causes Blindness?
Normal vision depends on a multi-faceted, complex process. Light enters the eye through the cornea and lens, with the iris helping to focus the image. The light is projected onto the back wall of the eye, where it is perceived by millions of tiny nerve endings that make up the retina. From here, the retina translates the images into nerve impulses that are transmitted to the brain through the optic nerve.
When any of these eye parts are damaged, either through illness or injury, blindness can occur:
- The lens may cloud, obscuring the light entering the eye.
- The eye’s shape can change, altering the image projected onto the retina.
- The retina can degrade and deteriorate, affecting the perception of images.
- The optic nerve can become damaged, interrupting the flow of visual information to the brain.
What Qualifies as Blindness?
People who are going blind often first deal with vision impairment, which then progresses into blindness. Blindness can affect one or both eyes, and doesn’t necessarily cause total darkness. Many people who are considered blind can still see some light or shadows, but cannot see anything clearly.
Likewise, “legal blindness” does not mean that a person cannot see anything, but that their vision is so impaired that they need a lot of help perceiving images.
The United States typically defines someone as legally blind when the person’s central vision has degraded to 20/200, or the person has lost peripheral vision so that he sees less than 20 degrees outside of central vision. Normal vision is 20/20, and people can usually see up to 90 degrees with their peripheral vision. An estimated 1.1 million people in the United States are considered legally blind.
Leading Causes of Blindness
Nearly all cases of blindness in the United States are caused by eye diseases, with less than 4 percent of blindness caused by eye injury or trauma. About 77 percent of people who have eye injuries fully recover, while another 11 percent have mild impairment.
Though the following eye diseases are common causes of blindness, you should not assume you are going blind if you have any of these conditions. There are treatments available for each condition — some more treatable than others.
Cataracts occur when the normally crystal clear lens of the eye becomes cloudy. This causes blurry vision, faded colors, and problems seeing through glare. Cataracts are the world’s No. 1 blindness cause, and more than 22 million Americans have cataracts in one or both eyes. A person’s risk of developing cataracts increases as he grows older: By the time they are 80 years old, more than half of all Americans either have a cataract or have undergone cataract surgery.
People with cataracts can deal with the disease at first through the use of special glasses, magnifying lenses, and brighter lighting. Those with advanced cataracts can undergo surgery to replace the clouded natural lens with an artificial one.
Glaucoma usually occurs when the fluid pressure inside one or both eyes slowly begins to increase. This pressure damages the optic nerve and the retina, causing a gradual decrease in peripheral vision. Experts estimate that about 2.3 million people in the United States have been diagnosed with glaucoma, while another 2 million have glaucoma but are not aware of their deteriorating eyesight.
Vision loss due to glaucoma cannot be reversed, but the disease can be managed through the use of prescription eye drops or surgery. It is important to have regular eye exams so you can catch glaucoma early, because treatment can save your vision.
Macular degeneration involves the gradual deterioration of the macula, or the nerve endings in the retina that are crucial for sharp central vision. People with this condition deal with blurring and blind spots in their central vision. This is the most common cause of blindness in seniors, affecting more than 10 million Americans.
There is no cure for macular degeneration, but treatments are available to slow its progress. These include combination vitamin therapy, laser surgery, photodynamic therapy, and special medications that are injected into the eye.
Diabetic retinopathy occurs when the systemic damage caused by diabetes begins to affect the retina. Specifically, the blood vessels that nourish the retina can be negatively affected by diabetes, causing vision loss through bleeding and damage to the retina. More than half of the 18 million Americans who have diabetes are affected by diabetic retinopathy to some extent.
The best treatment for diabetic retinopathy is close control of diabetes. If the disease becomes more advanced, patients can undergo eye surgery to protect their sight.