Common Eye Diseases and Causes of Vision Loss
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 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.
Amblyopia
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.
What should you 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 very common cause of vision loss in one eye among children and young adults.
Strabismus
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).
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.
What should you know about age-related macular degeneration (AMD)?
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 to 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). Eating healthy diet, exercising, and avoiding smoking can reduce the risk of AMD.
Cataract
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.
What should you 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, and this surgery 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.
Glaucoma
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.
What should you know about glaucoma?
Glaucoma can be controlled and vision loss 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.
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 no proliferative retinopathy (microaneurysms), moderate no proliferative retinopathy (blockage in some retinal vessels), severe no proliferative 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.
What should you 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 each year, but only about two thirds receive the recommended exam. Moreover, good management of diabetes by 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.
Vision Loss Among Top Ten Disabilities
An analysis of the 1999 Survey of Income and Program Participation (CDC, 2001) revealed blindness or vision problems to be among the top 10 disabilities among adults aged 18 years and older. Vision loss has serious consequences for the individual as well as those who care for and about people who have compromised vision because it impedes the ability to read, drive, prepare meals, watch television, and attend to personal affairs. Reduced vision among mature adults has been shown to result in social isolation, family stress, and ultimately greater tendency to experience other health conditions or die prematurely (Ellwein, Friedlin, McBean, & Lee, 1996).
Vision Loss and Age
Infancy and Childhood (Birth to Age 18)
In the United States, the most prevalent disabling childhood conditions are vision disorders including amblyopia, strabismus, and significant refractive errors. Early detection increases the likelihood of effective treatment; however, less than 15% of all preschool children receive an eye exam, and less than 22% of preschool children receive some type of vision screening. Vision screening for children scored on par with breast cancer screening for women.
Other eye diseases affecting this age group include retinopathy of prematurity (ROP), congenital defects, diabetic retinopathy (DR), and cancers such as retinoblastoma.
Adults Younger Than Age 40
Vision impairments in people younger than age 40 are mainly caused by refractive errors, which affect 25% of children and adolescents, and accidental eye injury. Approximately 1 million eye injuries occur each year, and 90% of these injuries are preventable. More than half (52%) of all patients treated for eye injuries are between ages 18 and 45 and almost 30% of those are 30–40 years (McGwin, Aiyuan, & Owsley, 2005. Additionally, diabetes affects this age group and is the leading cause of blindness among the working-age group 20–74.
Racial disparities occur in prevalence and incidence of some eye conditions. For example, among specific high-risk groups such as African Americans, early signs of glaucoma may begin in this age group, particularly if there is a family history for glaucoma. Lifestyle choices adopted during this period may adversely affect vision and eye health in later years (e.g., smoking, sunlight exposure).
Adults Older Than Age 40
American adults aged 40 years and older are at greatest risk for eye diseases; as a result, extensive population-based study data are available for this age group. The major eye diseases among people aged 40 years and older are cataract, diabetic retinopathy, glaucoma, and age-related macular degeneration. These diseases are often asymptomatic in the early treatable stages. The prevalence of blindness and vision impairment increases rapidly with age among all racial and ethnic groups, particularly after age 75 (Prevent Blindness America, 2002).
Although aging is unavoidable, evidence is mounting to show the association between some modifiable risk factors (i.e., smoking, ultraviolet light exposure, avoidable trauma, etc.) and these leading eye diseases affecting older Americans. Additional modifiable factors that might lend themselves to improved overall ocular health include a diet rich in antioxidants and maintenance of normal levels of blood sugar, lipids, total cholesterol, body weight, and blood pressure combined with regular exercise.
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