5 Diseases That Can Lead to Blindness

Our most dominant sense -- sight -- is a surprisingly fragile thing. There are many ways it can be reduced or lost entirely, and certain health conditions can greatly increase your risk of someday going blind.

What Does Blindness Mean?

The U.S. National Library of Medicine reports that "blindness is a lack of vision. It may also refer to a loss of vision that cannot be corrected with glasses or contact lenses." Though the concept of blindness commonly brings to mind a total loss of sight -- a darkness that's impenetrable, which is referred to as complete blindness -- in reality, there are varying levels and degrees of blindness. Partial blindness is the term used to describe a limitation to vision.

Randall McLaughlin, a doctor of optometry and associate professor of optometry at The Ohio State University Wexner Medical Center, says that there's also the concept of "legal blindness." People who are legally blind have "vision that is not better than 20/200 in the better eye with correction," meaning glasses or contact lenses.

Scoring a 20/20 on a vision test means you have perfect sight. As your sight decreases, the bottom number increases. A score of 20/200 means that a person can see at 20 feet what a person with perfect sight sees at 200 feet.

Many people who are defined as legally blind are still able to see shapes, color and movement, but there can be some variation in what it means to be blind, legally or otherwise, and there are varying degrees of visual impairment:

-- Moderate visual impairment is defined as visual acuity (what you see straight ahead) of 20/70 to 20/160.

-- Severe impairment is 20/200 to 20/400 or 20 degrees or less of functional visual field. People whose vision acuity falls here are legally blind.

-- Profound impairment is 20/500 to 20/1000 or 10 degrees or less of functional visual field. This is also a level of legal blindness.

Another term related to vision loss is low vision, which means that vision loss is great enough that it makes performing everyday tasks difficult or impossible.

[See: 7 Things to Know if You've Received a Diabetes Diagnosis.]

In all of these instances, there are certain eye diseases and conditions that make it more likely that you will struggle to see.

The five most common diseases that can lead to vision loss or blindness:

-- Diabetic retinopathy.

-- Age-related macular degeneration.

-- Cataracts.

-- Glaucoma.

-- Eye injury or trauma.

"The leading causes of blindness and low vision in the United States are primarily age-related eye diseases, says Barbara Horn, a doctor of optometry and president of the American Optometric Association. "The potential to rehabilitate vision will depend on the diagnosis, degree of diagnosis and length of diagnosis," she adds. Horn also notes that "early intervention via regular visits with a doctor of optometry is key to prevent visual impairment and optimize early treatment, if needed."

Diabetic Retinopathy

Diabetic retinopathy is a common eye disease that's associated with diabetes, a chronic disease that features elevated blood sugar levels. The Centers for Disease Control and Prevention reports that diabetes is the seventh leading cause of death in the U.S. and affects more than 30 million people, or 9% of the U.S. population. There are different types of diabetes, but the National Institute of Diabetes and Digestive and Kidney Disorders reports that all can threaten eye health.

Because the diabetic body is unable to regulate blood sugar levels, this causes damage to a number of organs and body systems. The blood vessels that support the retina, which is the thin film of tissue at the back of the eye that receives visual information and passes it on to the optic nerve, are particularly susceptible to the ravages of diabetes.

"Diabetic retinopathy is a serious, sight-threatening complication of diabetes and the leading cause of blindness in American adults aged 20 to 74 years," Horn says. The damage caused by diabetic retinopathy is progressive and can start subtly. But over time, "diabetes damages small blood vessels throughout the body, including the retina. Diabetic retinopathy occurs when these tiny blood vessels leak blood and other fluids. This causes the retinal tissue to swell, resulting in cloudy or blurred vision."

Diabetic retinopathy is usually present in both eyes at the same time, and the longer a person has diabetes, the more likely they are to develop the condition. People who also have high blood pressure and elevated cholesterol levels are also at higher risk. African Americans and Hispanics are also at greater risk for developing diabetic retinopathy, Horn says.

The National Eye Institute reports that "more than 2 in 5 Americans with diabetes have some stage of diabetic retinopathy." Frequent visits to an ophthalmologist or optometrist to monitor the health of your eyes is a critical component of diabetes management, Horn says, noting that "early detection and treatment can limit the potential for significant vision loss from diabetic retinopathy. The goal of any treatment is to slow or stop the progression of the disease."

To that end, managing your diabetes to prevent diabetic retinopathy from starting in the first place is always the best option for maintaining your sight long term. Horn says that diabetics should:

-- Take your prescribed medications.

-- Stick to a healthy diet.

-- Exercise regularly.

-- Control high blood pressure.

-- Avoid alcohol and smoking.

Though there isn't a specific diet that you should eat to preserve your eye health, McLaughlin says your retinas -- like the rest of your body -- benefit from "a good, balanced diet," rich with fresh fruits and vegetables.

In fact, in September 2019, it was widely reported that a teenager in the United Kingdom who had subsisted on a limited diet of potato chips, French fires and processed pork products had become legally blind as a result of his poor eating habits. This is an extreme case of optic neuropathy, but the point is, eating a healthy diet is good for your eyes as well as the rest of your body.

Even those who take very good care of themselves may develop diabetic retinopathy over time. If it happens to you, know that there are treatments available, and these can improve your vision or prevent you from losing more sight. Treatments for diabetic retinopathy include:

-- Injections. Medications injected directly into the eye can "decrease inflammation and stop the formation of new blood vessels, Horn says.

-- Laser treatments. These treatments can "seal leaking blood vessels or discourage other blood vessels from leaking," Horn says.

-- Eye surgery. In advanced cases of diabetic retinopathy, more involved surgical procedures may be warranted, Horn says. In these procedures, the doctor will "remove and replace the gel-like fluid in the back of the eye, called the vitreous. Surgery may also be needed to repair a retinal detachment," if the retina has separated from the back of the eye.

[READ: Why People With Brown Eyes May Be at Higher Risk for SAD]

Age-Related Macular Degeneration

AMD is the primary cause of severe vision loss in adults over age 50, Horn says. The CDC estimate that about 1.8 million people have AMD. Another 7.3 million are at substantial risk for vision loss from AMD. "Caucasians are at higher risk for developing AMD than other races. Women also develop AMD at an earlier age than men," Horn notes.

This chronic condition related to aging affects the macula, a part of the retina that provides central vision and helps your eye focus on objects straight ahead. "AMD is a loss of this central vision," Horn says.

There are two types of macular degeneration:

-- Dry (atrophic) AMD.

-- Wet (exudative) AMD.

"Most people with macular degeneration have the dry form," Horn says. In this form of AMD, "the tissue of the macula gradually becomes thin and stops working properly." The less common wet form "occurs when fluids leak from newly formed blood vessels under the macula. This leakage blurs central vision. Vision loss can be rapid and severe."

Symptoms of AMD may include:

-- Gradual loss of ability to see objects clearly.

-- Shape of objects appears distorted.

-- Straight lines look wavy or crooked.

-- Loss of clear color vision.

-- A dark or empty area in the center of vision.

Some of these changes may be subtle in the early stages of the disease and may be overlooked, Horn says. If you experience any of these symptoms, Horn urges you to contact your eye doctor immediately. Making an annual visit to the eye doctor can also help catch AMD in its earliest stages, before vision loss occurs. "While central vision that is lost to macular degeneration most often cannot be restored, low-vision devices, such as telescopic and microscopic lenses, can maximize remaining vision."

Although there is no specific treatment for dry AMD, "studies have shown a potential benefit from vitamin supplements a healthy diet and cessation of smoking." In addition, some studies have shown a potential link between nutrition and the progression of dry AMD, Horn says. Therefore, "making dietary changes and taking nutritional supplements can slow vision loss."

Wet AMD can be treated with intraocular injections of anti-VEGF medications if it's detected early, Horn says. VEGF stands for vascular endothelial growth factor, which is a protein made by the body to promote blood vessel growth. These injections essentially help dry out the wet spot in the macula by shrinking abnormal blood vessels and preventing new ones from forming. In some rare cases, surgery may be performed for macular degeneration.

Cataracts

Cataracts are the term used to describe a clouding over of the natural lens in the eye. It's a natural process and it happens to everyone eventually; if you live long enough, you'll develop cataracts. The American Academy of Ophthalmology reports that by age 75, "approximately half of all Americans have cataracts."

Because it's so common, cataracts are the "leading cause of blindness worldwide and the leading cause of vision loss in the United States," Horn says. Although they can occur at any age and can be present at birth, it's often associated with aging. More than 24 million Americans 40 and older have cataract in one or both eyes. "The total number of people who have cataracts is estimated to increase to 30.1 million by 2020," Horn says.

Symptoms of cataracts include:

-- Gradual or progressive decrease in vision.

-- Loss of vision correction with glasses.

-- Cloudy or blurry vision.

-- Double vision.

-- Loss of color sensitivity.

-- Poor night vision.

There's not much that can be done to help you avoid developing cataracts, but avoiding smoking, protecting your eyes from UV light and controlling diabetes if you have it can slow the development of cataracts. Taking steroid medications long term may speed the development of cataracts.

In the U.S., surgery is the primary treatment for this very common disease and is one of the most common and effective surgeries performed. The National Eye Institute reports that "in about 90% of cases, people who have cataract surgery have better vision afterwards."

[See: When Contact Lenses Cause Vision Problems.]

Glaucoma

This eye disease is also typically related to age and is caused by progressive damage to the optic nerve. "The optic nerve is a bundle of about 1 million individual nerve fibers that transmits the visual signals from the eye to the brain," Horn says. The damage is caused by unusually high pressure in the eye.

The AAO reports that glaucoma affects more than 2.7 million Americans aged 40 and older, and it's more common among adults over age 60. "Glaucoma is the second-leading cause of blindness in the U.S.," Horn says, and it's usually diagnosed in people over the age of 40. However, there are a few different types of glaucoma and congenital glaucoma can impact infants.

There are two primary types of glaucoma:

-- Open-angle glaucoma.

-- Acute angle-closure glaucoma.

Primary open-angle glaucoma is the most common type of glaucoma. In this disease, the fluid pressure inside the eye increases, which causes progressive damage to the optic nerve and a loss of nerve fibers. Primary open-angle glaucoma usually develops slowly and with no symptoms. "Many people are not aware they have the condition until they have significant vision loss," Horn says. Early symptoms, if they do occur, include a loss of peripheral vision. "But it can advance to central vision loss," Horn says. If it's not treated, blindness may occur.

Acute angle-closure glaucoma is a less common form of the disease, and in these cases, vision loss typically occurs much more "abruptly due to a rapid increase of pressure in the eye," Horn says.

Other symptoms of acute angle-closure glaucoma may include:

-- Severe eye pain.

-- Nausea.

-- Redness in the eye.

-- Seeing halos or colored rings around lights.

-- Blurred vision.

Acute angle-closure glaucoma is "an emergency condition in which severe vision loss can occur quickly. Patients should consult their doctor of optometry immediately," Horn says.

Certain populations may have a higher risk of developing glaucoma, Horn says. "African Americans are significantly more likely to get glaucoma than Caucasians, and they are much more likely to suffer permanent vision loss. People of Asian descent and Native Alaskans are at higher risk of angle-closure glaucoma. People of Japanese descent are more likely to develop low-tension glaucoma."

A family history of glaucoma is another risk factor, as are certain medical conditions, including diabetes, high blood pressure and heart disease.

Other risk factors that can trigger glaucoma include:

-- Thinner corneas (the outer sheath that covers the pupil and iris) or optic nerve sensitivities.

-- Retinal detachment.

-- Eye tumors.

-- Eye inflammation.

-- Long-term use of certain medications, such as corticosteroids.

There are treatments available for glaucoma, and regular visits to the eye doctor can help detect the disease in its earliest stages before significant vision loss has transpired. "There is no cure for glaucoma and patients must continue treatment for the rest of their lives. Medication or surgery can slow or prevent further vision loss, however, vision already lost to glaucoma cannot be restored," Horn says.

[See: 13 Foods That Do Your Eyes Good.]

Eye Injuries or Trauma

Any kind of trauma to the eye can cause a loss of vision. This may include conditions such as eye stroke, in which the retina or optic nerve experiences a loss of blood flow. This typically causes temporary vision loss, but if the condition worsens or is not treated appropriately, that loss can become permanent.

Severe trauma, such as might be sustained in a car accident or other traumatic injury and exposures to certain chemicals, can also cause blindness either suddenly or after chronic exposure. Following common sense eye-safety procedures when working with hazardous materials or in dangerous settings can significantly reduce your risk of developing an eye injury and subsequent vision loss.

No matter which potential cause might be changing the way you see, "if you do notice a change to your vision, visit your doctor immediately," McLaughlin says.