Medically Reviewed By William C. Lloyd III, MD, FACS

What is cataract?

A cataract is a clouding or loss of transparency in the lens of the eye that interferes with vision. Cataracts usually develop as a result of normal aging and are most prevalent in people over 40. According to the National Eye Institute, half of all people in the United States develop cataracts by the age of 80.

The crystalline lens of the eye is composed of cells and special proteins that are initially clear. The lens is the driest soft tissue in the entire body with a very low water content. Cataracts develop when the adult lens begins to accumulate water and proteins within the lens begin to clump together and become denser. The formation of these protein bundles creates a discolored or opaque area in the lens and makes it difficult for light to pass through the eye to the retina. The cloudiness may affect only a small part of the lens. However, the cataract may progress over time, making it harder to see. As less properly focused light reaches the retina, vision may become dull and blurry.

Less commonly, an injury to the lens can cause cataracts. In some cases, cataracts are congenital, which means they are present at birth. Cataracts may also develop as a result of diabetes or extended use of certain medications, including corticosteroids. Cataracts due to aging, disease, or drugs tend to occur in both eyes, although the degree of severity may be different in the two eyes. A cataract caused by trauma will affect only the injured eye.

Cataracts generally develop over time and may get progressively worse as you age. In most cases, you most likely will not experience any symptoms until the cataract is advanced. Symptoms include gradually increasing haziness of vision and glare or halos from lights. Cataracts are not treated until they cause visual symptoms. Fortunately, cataract surgery is highly successful in restoring clear sight.

Cataracts generally do not indicate a medical condition that needs immediate attention. However, they can be a sign of chronic serious conditions such as diabetes. Seek prompt medical care if you have symptoms of cataracts that become bothersome or are associated with other symptoms.

What are the different types of cataract?

The National Eye Institute classifies cataracts into five primary types, based on the cause of the cataract:

  • Age-related cataract: The majority of cataracts are related to aging as a result of natural changes in the lens. Underlying conditions and other lifestyle factors can increase your risk for age-related cataract.
  • Traumatic cataract: An injured eye may develop a cataract immediately following the incident or several years later. Eye surgeries can also cause a cataract to form. 
  • Radiation cataract: Ultraviolet (UV) rays from the sun without the protection of sunglasses and radiation therapy to the upper body for cancer can damage the lens and lead to cataract. 
  • Pediatric cataract: Although rare, cataracts can be present at birth due to genetics or complications during pregnancy. Illness, eye injuries, eye tumors, radiation exposure or therapy, and steroid medications can also lead to cataracts in children.
  • Secondary cataract: Also known as posterior capsule opacification or after-cataract, secondary cataract can occur after successful cataract surgery when residual lens debris causes the formerly transparent lens capsule to become opaque. Technically, secondary cataracts aren’t exactly cataracts because the new lens itself is not changing. A simple laser treatment can treat secondary cataract.  

The American Academy of Ophthalmology also describes cataracts according to their location on the eye lens:

  • Nuclear cataract: This is the most common type of cataract and the most common type associated with aging. Nuclear cataracts develop in the center of the lens and can induce nearsightedness—a temporary improvement in reading vision that’s sometimes called “second sight.” This beneficial change in vision disappears as the cataract progresses. 
  • Cortical cataract: This type initially develops as wedge-shaped spokes in the cortex of the lens, with the spokes extending from the outside of the lens to the center. The spokes interfere with the movement of light and cause glare and loss of contrast. This type of cataract often can occur in people with diabetes, and it may impair vision so significantly that doctors recommend surgery. 

  • Subcapsular cataract: A subcapsular cataract (also called posterior subcapsular cataract) usually starts as a small opacity under the capsule, at the back of the lens. It can occur in people with diabetes, myopia, or retinitis pigmentosa, and in those taking steroids.

What are the signs and symptoms of cataract?

Cataracts are painless and produce only visual symptoms. If you have symptoms in any other part of your body along with cataracts, they are not caused by the cataracts themselves. However, they may be related to underlying diseases, such as diabetes, that can play a role in the development of cataracts.

Visual symptoms associated with cataracts

Visual symptoms associated with cataracts tend to gradually increase in severity. Common symptoms of cataracts include:

  • Blurred or double vision

  • Dulling of colors

  • Frequent need for changes in eyeglass or contact lens prescription

  • Glare or halos appearing around lights

  • Hazy vision

  • Poor nighttime vision

Symptoms that might indicate a serious condition

Cataracts themselves are not a serious condition related to your overall health. However, cataract formation may be induced or accelerated by serious underlying conditions or diseases that should be promptly identified and treated. Seek prompt medical care if you have symptoms of cataracts that become bothersome or are associated with other symptoms.

What causes cataract?

The crystalline lens is a remarkably dry tissue. The lens is basically a complex matrix of transparent cells. Cataracts develop when the lens accumulates water. Meanwhile, proteins in the lens, which are normally clear, begin to clump or aggregate. This process causes discoloration and loss of transparency in the lens. Eventually, the loss of transparency interferes with the passage of light rays through the lens to the retina, and vision becomes cloudy.

In most cases, cataract formation occurs because of normal aging. However, it may also be triggered by injury to the eye, eye surgery, exposure to radiation, or excess sun exposure. Cataracts may also be a congenital condition, meaning they’re present at birth.

What are the risk factors for cataract?

The most common risk factor for cataracts is age. Although people can develop age-related cataracts between ages 40 and 50 years, more severe vision changes do not typically occur until after age 60.

Several factors increase the risk of developing cataracts. Not all people with risk factors will get cataracts. Risk factors for cataracts include:

  • Age (over 40 years)

  • Diabetes

  • Excess alcohol use

  • Injury to the eye

  • Long-term use of allopurinol, a uric acid reducer to treat gout and kidney stones

  • Overexposure to ultraviolet (UV) light from sunlight

  • Prolonged use of corticosteroids (oral/systemic and topical eye drops), such as prednisone, prednisolone and betamethasone

  • Radiation therapy, such as for cancer or other conditions

  • Smoking

  • Vitrectomy, the surgical removal of the vitreous (the gel-like fluid that fills the eye), nearly always causes cataract to occur within 3 months. Vitrectomy is frequently performed for trauma, retinal detachment, diabetic eye disease, macular edema of any cause, macular pucker or macular hole formation, and other eye conditions.

How do you prevent cataract?

Although you cannot change the major risk factor for cataracts—age—you can take steps to modify lifestyle habits linked to cataract. You may be able to prevent or delay cataracts by:

  • Having regular eye exams by age 40, included a dilated eye examination by an ophthalmologist (a physician who specializes in the diagnosis and treatment of eye diseases)

  • Keeping your blood sugar levels under control if you have diabetes

  • Limiting your alcohol consumption: two drinks or less in a day for men or one drink or less in a day for women

  • Quitting smoking if you smoke

  • Talking with your eyecare professional about all medications you take. Some medications may increase your risk for cataract or affect other eye structures. Your eye doctor and healthcare professional may recommend a lower dosage or a different medication.

  • Wearing sunglasses with full-spectrum UV protection when outside

How do doctors diagnose cataract?

Protecting your eye health begins with regular eye exams with an ophthalmologist and optometrist. In addition to a complete medical history, including your current medications, an initial eye exam includes checks for color sensitivity, peripheral vision, glaucoma, and how well your pupils respond to light.

Tests to diagnose cataracts and other eye diseases include:

  • Visual acuity: This test evaluates the sharpness and clarity of your vision. It involves reading the common eye chart with one or both eyes. Your doctor may also have you look through a large lens refactor to determine which lenses make your vision better or worse.

  • Slit lamp test: Using a special magnifier and lamp, your eye doctor shines a vertical beam of light into your eye for an enlarged view of your cornea, iris, lens and other areas on the front of the eye. 

  • Dilated eye exam: Your eye doctor will put a few drops in your eyes to cause your pupils to enlarge. This allows a full view of the back of your eye, including your retina and optic nerve. With this test, your doctor can look for signs of cataracts, glaucoma, and other eye diseases.

What are the treatments for cataract?

Cataracts generally do not require treatment until they begin to affect your vision noticeably. Some minor symptoms of cataracts, including dulling of vision or small changes in visual acuity, may be improved by nonsurgical approaches, such as improved lighting or changes in eyewear prescriptions.

Once your cataracts begin to interfere with your ability to drive at night, read, or watch TV, doctors may recommend a surgical procedure to treat them.

During cataract surgery, your eye surgeon will completely remove the contents of the lens of your eye and replace it with a synthetic lens, called an intraocular lens, which will restore the clarity of your vision.

How does cataract affect quality of life?

Visual impairment due to cataract negatively affects quality of life. At later stages, cataracts can cause difficulties with routine activities, such as driving at night, reading, watching TV, using a computer, or leaving the house to socialize, grocery shop, or run errands. Poor vision can also put you at risk for falls, and the associated effects of vision loss can lead to isolation and depression.

Contact your healthcare professional if your cataracts are impairing your vision or affecting your quality of life. Together, you can discuss treatment options to restore your vision and get you back to your normal routine.

What are the potential complications of cataract?

Cataracts affect only your eyes and are not life-threatening. However, cataracts may form because of an underlying chronic disease, such as diabetes, that may have serious complications.

You can help minimize your risk of serious complications by following the treatment plan you and your healthcare professional design specifically for you.

Complications of untreated cataracts include loss of vision and blindness. Discuss your cataract symptoms with your ophthalmologist.Together you can discuss the risks and benefits of cataract surgery to fix impaired eyesight.

Was this helpful?
  1. Cataracts. American Academy of Ophthalmology. 
  2. Cataracts. JAMA Patient Page.
  3. Cataracts. National Eye Institute.
  4. Vitrectomy. Information for patients. Oxford Eye Hospital.
  5. Ahmad R., Mehta H. The ocular adverse effects of oral drugs. Aust Prescr 2021;44:129-36. First published 13 August 2021.
  6. Tierney LM Jr., Saint S, Whooley MA (Eds.) Current Essentials of Medicine (4th ed.). New York: McGraw-Hill, 2011.
Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Nov 7
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