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Written by Ada’s Medical Knowledge Team

Updated on

What are cataracts?

A cataract is a clouding of the eye’s lens which leads to a decrease in vision and, in some cases, possible blindness. The condition occurs when protein clumps in one or both eyes prevent the retina from receiving clear images. 1 Cataracts generally affect older people, but can also be present from birth, be brought about by exposure to radiation or trauma, as well as through complications from surgery. 2

Cataracts are among the main causes of blindness globally and are one of the most common reasons for loss of vision in people over 40. 3 Cataracts can be treated through surgery, and steps can be taken to help prevent the onset of the disorder.

Types of cataracts

There are several types of cataracts, each classified by how and where they develop in the eye: 4

  • Nuclear cataracts form in the center (nucleus) of the lens and typically cause the eye to become brown or yellow. They are normally associated with aging.
  • Posterior capsular cataracts affect the back of the eye and typically form very quickly.
  • Cortical cataracts form in the lens cortex which surrounds the nucleus. They are white and wedge-shaped opacities.
  • Congenital cataracts are a rare form that develops in childhood or are present at birth.
  • Radiation cataracts are brought about by exposure to radiation, typically as a result of cancer treatment.
  • Traumatic cataracts are brought about by damage to the eyes and can sometimes develop some time after the initial trauma.
  • Secondary cataracts are a result of medications or disease. These include the steroid prednisone, diabetes, and glaucoma.

Symptoms of cataracts

Cataracts typically develop slowly, meaning the symptoms may be difficult to detect or confused with normal signs of aging. The symptoms include:

  • Blurred, clouded or dimmed vision
  • Sensitivity to light and glare, particularly at night
  • Objects appear yellow-tinged or faded in color
  • Halos appearing around lights
  • Changes in glasses prescription

Occasionally, when cataracts first develop, it can lead to an improvement in nearsightedness. This phenomenon is known as “second sight” and is a temporary occurrence that will disappear as the condition develops. 5

Worried you may have this condition? Start a free symptom assessment on the Ada app.

Causes of cataracts

The lens of the eye filters light onto the retina, allowing for clear and focussed vision. Largely, it is made from water and proteins. Cataracts are brought about when these proteins begin to clump in the lens, leading to blurred, faded and cloudy vision that can worsen over time. This clumping is commonly a result of aging, yet it is not clear why some people and not others are affected.

There are, however, some factors that may increase an individual’s chances of developing cataracts, including: 6

  • Exposure to ultraviolet radiation, from sunlight or radiation therapy
  • Diabetes
  • Eye conditions such as uveitis and glaucoma
  • Eye injury or surgery
  • Use of corticosteroids
  • A family history of cataracts

Other factors that are also thought to be linked to the development of cataracts include:

Diagnosing cataracts

Cataracts are diagnosed through a full eye examination carried out by an optometrist or ophthalmologist. Those experiencing problems with their sight should visit an eye care professional as soon as possible. Moreover, people over 40 should undergo an eye test at least once every two years. 7

Cataracts treatment

If the symptoms of cataracts are mild, an altered prescription, e.g., for different glasses or contact lenses, may be effective in correcting an individual’s vision. However, it is typical for cataracts to worsen over time. If this happens, it is likely that surgery will be necessary. 8

Cataracts surgery is a common procedure and usually carried out under local anaesthetic. Most people who undergo cataract surgery will see a significant improvement in their vision, with 9 out of 10 people achieving between 20/20 and 20/40 vision afterwards. However, most surgeons will focus on correcting long-distance sight, meaning glasses may still be needed to see things close at hand.

Good to know: The terms 20/20 and 20/40 are visual acuity measurements.

This is usually measured using the Snellen visual acuity system:

  • The top number of the fraction refers to the viewing distance between the patient and the eye chart.
  • The bottom number of the fraction refers to the distance at which a person with ideal vision would be able to see the figures on the eye chart clearly.

A person with 20/40 vision can therefore see figures on the eye chart clearly at a distance of 20 feet, whereas a person with ideal vision could see the same figures clearly, from a distance of 40 feet away from the eye chart.

In the United States, the distance at which visual acuity is measured, is typically 20 feet. In other countries, this distance is generally six meters, and a person’s visual acuity may therefore be expressed as a fraction of six.


The risk of complications during and after cataract surgery is small. The most common complication is posterior capsule opacification (PCO) brought about when skin or membrane grows over the implanted lens, resulting in a return of clouded or impaired vision. PCO can be corrected with laser surgery. 1 8

There are other risks that are far less common. Risks during the operation include:

  • Tearing of the lens
  • Inability to remove the cataracts
  • Bleeding of the eye
  • Accidental damage to other areas of the eye

Risks following the operation include:

  • Inflammation of the eye
  • Retina swelling
  • Cornea swelling
  • Retinal detachment
  • Infection

If complications become apparent after surgery, a doctor should be contacted as soon as possible. In most cases, complications can be rectified with treatment or further surgery.

Cataracts prevention

Although there is no guaranteed way to prevent cataracts, there are some preventative measures that can be undertaken to reduce the risk. They include: 9

  • Having your eyes checked regularly
  • Eating a healthy diet rich in vitamins
  • Quitting or cutting down on smoking
  • Reducing your alcohol intake
  • Avoiding prolonged use of corticosteroids

Cataracts FAQs

Q: Is cataract extraction possible?
A: Yes, cataract extraction is carried out through surgery. The procedure is considered routine and is a success in most cases, leading to between 20/20 and 20/40 vision. 10

Q: Do cataracts lead to blindness?
A: Cataracts cannot be reversed but it can be treated effectively through surgery. If, however, the condition is left untreated, it can lead to blindness.