Cataracts 101: Types and causes

Imagine if the sharp images you normally see started to become blurry. That’s a classic symptom of cataracts, the most common correctible cause of vision loss among Canadians. As you get older, changes in the lens of your eye can lead to cataracts that obscure vision. While age-related cataracts are the most common type, they also can be caused by eye injuries, diabetes, steroid drugs or excessive sun exposure.

Age-related cataracts

Colour picture of an elderly couple using a laptopMost cataracts occur as a result of aging, but it is possible to develop age-related cataracts as early as 40. Age-related cataracts usually progress slowly and don’t affect your vision at first. As a cataract develops and the lens clouds over, your vision blurs and this can make driving, cooking and other activities difficult.

Age-related cataracts form in two ways. With aging, protein fibres in the lens break down and clump together, blocking some of the light that would normally enter through the lens so that your distance vision becomes duller and cloudier. Your reading vision may improve temporarily, but then worsen as the cataract develops. Also, the lens may turn yellowish or brown, making it harder to read and distinguish dark colours such as dark blue and purple. Eating a healthy diet, quitting smoking and protecting your eyes from bright sunlight may delay or reduce the risk of developing age-related cataracts.

Traumatic cataracts

This type of cataracts, caused by eye injuries, can happen at any age. A traumatic cataract may occur as a result of a blunt force injury (from a finger, fist or tennis ball, for example) that directly damages the lens. It can result from a penetrating injury, in which your eye is pierced by a sharp object, such as a knife, a splinter or a pencil. A traumatic cataract may form soon after an injury or months to years later. For tips on protecting your eyes from injuries, see the Eye Safety section on CNIB’s website.

Radiation cataracts

Prolonged exposure to ultraviolet radiation (UV) from sunlight is another cause of cataracts. Studies have shown that outdoor workers, such as crab fishermen and farmers, are more susceptible to cataracts than indoor workers. Wear sunglasses with 100% UVA and UVB protection in bright sunlight (both in winter and summer) to reduce your risk of developing this type of cataracts – and make sure that children do as well.

Congenital cataracts

Some babies are born with cataracts. These may be inherited or caused by an infection or illness that a mother has during pregnancy, such as German measles (Rubella). A cataract at birth can stop the eye from learning to see, so surgical treatment is often needed to allow the child’s visual system to develop normally.

Secondary cataracts

Secondary cataracts are cataracts that form as a result of another medical condition, such as diabetes. They can develop after surgery for glaucoma or after eye infections such as uveitis and retinitis. Long-term use of oral steroids, like prednisone, also increases your risk.

Cataracts in different parts of the lens

In addition to classifying cataracts by cause, they are also distinguished by their location in the lens. The lens has three different layers: the nucleus, the softer cortex that surrounds it and the outer capsule that covers the lens.

A nuclear cataract is the most common type of age-related cataract. It occurs in the centre of the lens’s nucleus, which hardens with age and may turn yellow or brown over time. If you have this type of cataract, you’ll have trouble seeing at a distance and possibly identifying dark colours.

A cortical cataract begins as wedge-shaped spokes on the outer edge of the lens’s cortex and progresses to its centre, causing problems with glare and contrast. Diabetics can develop this type of cataract, which may affect distance and near vision.

A subcapsular cataract forms under the capsule on the surface of the lens. It can interfere with reading, affect your sight in bright light and cause glare or halos around light at night. You might be at risk for this type of cataract if you use corticosteroids or injure your eye, or if you have extreme nearsightedness, retinitis pigmentosa or diabetes.

Be sure to bring along the Cataract Doctor Discussion Guide to help you ask the right questions at your next doctor's appointment.