Basics of Vision and Eye Health

Common Eye Disorders and Diseases

More than 4.2 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.

Refractive Errors

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, which occurs between the age of 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. The National Eye Institute states that proper refractive correction could improve vision among 150 million Americans.

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 of 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 vessels 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 over time as part of the aging process, gradually blurring central vision. The dry form is more common and accounts for 70–90 percent of cases of AMD, and it progresses more slowly than the wet form. Over time, as fewer 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 will reach 2.95 million in 2020. In addition, AMD is the leading cause of permanent impairment of reading and fine or close-up vision among people aged 65 years and older.


A 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 various causes and can be present at birth. Although treatment for the removal of the 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 percent ) Americans aged 40 years and older have a cataract in one or both eyes, and 6.1 million (5.1 percent ) 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

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 the deprived retina from blood supply leading to growing new blood vessels), and proliferative retinopathy (most advanced stage) (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. In addition, early diagnosis of DR and timely treatment reduce the risk of vision loss; however, as many as 50 percent 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. In addition, an estimated 4.1 million and 899,000 Americans are affected by retinopathy and vision-threatening retinopathy, respectively.


A 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 progresses slowly over a long period without the person noticing vision loss until the disease is very advanced; that is why it is called a “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 called “lazy eye,” is the most common cause of vision impairment in children. Amblyopia is the medical term for 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 cataracts.

Unless it is successfully treated in early childhood, amblyopia usually persists into adulthood. As a result, it is the most common cause of permanent one-eye vision impairment among children and young and middle-aged adults. An estimated 2 percent –3 percent of the population suffer from amblyopia.


Strabismus involves an imbalance in the positioning of the two eyes. Strabismus can cause the eyes to cross in (esotropia) or turn out (exotropia) (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. However, in more than half of these cases, the problem is present at or shortly after birth (congenital strabismus) (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) (one type of amblyopia).

Vision Health Frequently Asked Questions

Can I do anything about my chances of vision loss?

It is estimated that half of the visual impairment and blindness can be prevented through early diagnosis and timely treatment. Unfortunately, despite cost-effective treatment and eye preservation interventions, the number of potentially blinding eye diseases continues to escalate. Increased awareness can help — remind family members and friends at higher risk for eye diseases and vision loss to have their eyes examined regularly.

What are the major causes of vision loss for individuals aged 40?

The prevalence of blindness and visual impairment increases with age in all racial and ethnic groups. The major eye diseases among people 40 years and older are age-gelated macular degeneration, cataract, diabetic retinopathy, and glaucoma.

What should I know about diabetic retinopathy?

Diabetic retinopathy is the leading cause of blindness among working-age (ages 20–74) Americans. It is caused by changes in the blood vessels of the retina. Efficacious and cost-effective interventions to detect and treat diabetic retinopathy are available. Individuals with diabetes should have a dilated eye exam yearly, but only about two-thirds receive the recommended exam. Moreover, good management of diabetes through good glucose, blood pressure, and lipid control can reduce the progression of diabetic retinopathy. People at risk for diabetes should modify their lifestyle to delay or prevent diabetes by good diet and physical activity.

What should I know about cataracts?

Cataracts are a major cause of vision loss. Among Americans aged 40 years and older, 24.4 million have cataracts. Cataract removal surgery can restore vision, which is highly cost-effective; however, among African Americans, unoperated senile cataracts remain a major cause of blindness. Some possible risk factors other than age could be diabetes, smoking, and prolonged exposure to sunlight.

What should I know about age-related macular degeneration (AMD)?

About 2,000,00 Americans aged 50 years and older have AMD. Treatment with zinc and antioxidants has been shown to reduce the risk and progression of advanced AMD among people aged 50 years and older. The greatest risk factor is age; however, other risk factors include smoking, obesity, family history, race (white), and gender (female) (female). Eating a healthy diet, exercising, and avoiding smoking can reduce the risk of AMD.

What should I know about glaucoma?

Glaucoma can be controlled, and vision loss can be stopped by early detection and timely treatment. Nevertheless, half of all people with glaucoma are not diagnosed, and glaucoma is still the number-one blinding disease among African Americans. People who are at risk for glaucoma are African Americans aged 40 years and older, everyone older than age 60, especially Mexican Americans, and people with a family history of glaucoma. People falling in these groups should have a dilated eye exam every two years by an eye care professional.

What should I know about amblyopia or lazy eye?

Amblyopia (or lazy eye), is the most common cause of vision loss among children. It affects 2 to 3 out of 100 children. If it is not treated timely and properly, it can stay through adulthood. It is a common cause of vision loss in one eye among children and young adults.


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