What Causes Vision Loss?

True vision loss means that you have permanently limited or complete loss of vision—and that surgery, glasses and/or contact lenses could not improve your vision to normal levels. It’s estimated that 93 million adults in the U.S. are at high risk for severe vision loss—and only 50% of them have visited an eye doctor in the past 12 months^[2]Fast Facts of Common Eye Disorders. Centers for Disease Control and Prevention. Accessed 7/14/2021. .

For clear vision, light must travel an uninterrupted path from the front of the eye through the cornea and lens to the retina or back of the eye. Anything that blocks light from passing through these structures or disrupts the transmission of nerve impulses from the back of the eye to the brain can cause vision loss.

How Is Vision Loss Diagnosed?

Vision loss is diagnosed with a complete eye examination by an ophthalmologist or optometrist. The American Optometric Association says complete eye exams should begin at 6 to 12 months of age and occur every one to two years thereafter. After 40 is when early signs of disease or changes in vision typically appear, so if you’re at higher risk, get an eye exam every year. At age 65, examinations are recommended annually for every person regardless of risk level.

It’s essential to find eye disease sooner rather than later—early treatment can help preserve your vision.

During a comprehensive eye exam, the physician gathers your medical history and performs several tests, which assess:

• Acuity (reading a chart)
• Pupil response to light
• Color vision, binocular vision and depth perception
• Anatomical structures of the eye (via a slit lamp, a type of microscope)
• Retinal fundus examination (via dilation and retinal imaging)

There are many causes of vision loss, but “the most common cause of vision loss I see is cataracts,” says James  T.  Lim​, a doctor of optometry who practices in Madison, Alabama. “Most cases are due to normal aging changes. While the effects of aging are inevitable, many conditions can raise the risk of early cataracts, such as excess exposure to ultraviolet sunlight, health conditions like diabetes and high blood pressure, smoking, trauma, certain medications and poor nutrition,” he says

Research also shows cataracts and undercorrected refractive errors are among the three leading causes of treatable vision loss^[3]GBD 2019 Blindness and Vision Impairment Collaborators, Vision Loss Expert Group of the Global Burden of Disease Study. Causes of blindness and vision impairment in 2020 and trends over 30 years, and prevalence of avoidable blindness in relation to VISION 2020: the Right to Sight: an analysis for the Global Burden of Disease Study. Lancet Glob Health. 2021;9(2):e144-e160. .

Cataracts

A healthy eye lens is usually clear—a cataract is a clouding of the lens. This cloudiness blocks the passage of light to the back of the eye, making images look blurry and eventually causing vision loss.

Part of the aging process, cataracts are caused by long-term exposure to UV rays, injury, disease and lifestyle choices, such as smoking and excess alcohol use. Cataracts may appear as a white, gray or yellow-brown discoloration of the lens. Correction involves surgical removal of the  lens and placement of an artificial lens.

Refractive Errors

Refractive errors are a group of disorders that impair vision because the cornea can’t focus light or images onto the back of the eye correctly. These errors are more common in older populations but can occur at any age.

Myopia: Also known as nearsightedness, myopia symptoms include eye strain, headaches, squinting and difficulty seeing objects far away.

Hyperopia: With this refractive error—also known as farsightedness—your eye doesn’t bend or focus light properly to see images clearly. Distant objects may look clear, but close objects may be blurred. With significant hyperopia, vision can be blurry at any distance, near or far.

Presbyopia: This refractive error is characterized by the gradual loss of ability to see things clearly up close. It’s a normal part of aging—after age 40, you may start to notice you hold reading materials further away in order to see them clearly, which is an indication of presbyopia.

Astigmatism: An astigmatism is an imperfection in the curvature of the eye. The normal eye is round but with astigmatism, it’s shaped more like an American football. If the eye isn’t curved evenly, light rays cannot focus correctly. You may notice blurring or distortion near and far with astigmatism.

Glaucoma

Glaucoma is a chronic, progressive condition of increased intraocular pressure on the optic nerve that may progress to permanent loss of vision^[4]Dietze J, Blair K, Havens SJ. Glaucoma. In: StatPearls. StatPearls Publishing; 2020. Accessed 7/10/2021. . Anyone can develop glaucoma, but certain groups are at higher risk, including African Americans over the age of 40, all people over the age of 60 and people with a family history of glaucoma and diabetes.

The most effective way to treat glaucoma is to reduce your eye pressure. Treatments include medications, lasers and surgery.

Macular Degeneration

This condition damages the back of the eye, or retina, causing central vision loss and distortion. Smoking and a family history of macular degeneration place you at higher risk. There are “wet” and “dry” types of macular degeneration, and treatment depends on the kind you have.

“Dry” macular degeneration is a condition in which layers of the macula become thin, atrophy (dry out) and lose their function. “Wet” macular degeneration is a less common condition in which new blood vessels grow behind the retina. They are weak and, therefore, leak fluid and blood. The leaking can cause scar tissue to form and the retina to stop functioning.

Diabetic Retinopathy

Diabetic retinopathy is a condition that damages the retina in people with high blood sugar levels. Uncontrolled blood sugar and elevated blood pressure can cause problems in the retina, such as abnormal vessel growth and bleeding. If you have diabetes or poor blood sugar control, you are at risk for diabetic retinopathy. Risk also increases the longer you’ve had diabetes.

With proper screening, good blood sugar levels, blood pressure control and early intervention, you can avoid severe vision loss.

Sudden vision loss has many causes, and severe or life-threatening eye emergencies can be painful or completely painless. Call your eye doctor immediately if you experience any of the following symptoms:

• Changes in the eye’s appearance
  • Pupil size
  • Cherry red area at the center of macula
  • Swelling
• Sudden onset halos around lights
• Feeling of foreign body in the eye^[5]Bhavsar A. Why does it feel like something is rubbing against my eye when I blink?. Aao.org. Accessed 7/11/2021.
• Sudden headache
• Vision changes
  • Blurring
  • Distortion
  • Floaters
  • Black dots
  • Flashes of light
  • A missing piece of your field of vision

Most severe forms of vision loss are painless, but a lack of pain shouldn’t diminish your urgency in seeking medical care quickly^[6]Ogun O. Red flags in neuro-ophthalmology. Community Eye Health. 2016;29(96):64-65. . Some types of vision loss can only be successfully treated in a short amount of time.