Cataracts can be age-related, congenital (present at birth or shortly after), related to certain ocular or medical conditions or trauma-related.
The eye lens—the clear part of the eye that helps focus light or images on the back of the eye—has a unique structure and is vulnerable to damage. It’s composed of water and crystallins, or proteins, that, along with the complex structure, provide transparency to the lens.
As the lens begins to age, the nucleus, or center, compresses and hardens and begins to lose its transparency. When the protein clumps, it begins to cloud, causing opacity of the lens. At this point, the light that passes through a lens with a cataract is not clear, resulting in blurred images.
Types of Cataracts
There are five main types of cataracts, according to the National Eye Institute:
- Age-related cataracts. “The most common type of cataract I see are nuclear sclerotic cataracts associated with aging or, as I like to tell my patients, increased wisdom,” says ophthalmologist Shameena Sikder, M.D., director of the Center of Excellence for Ophthalmic Surgical Education and Training and associate professor of ophthalmology at Johns Hopkins School of Medicine in Baltimore. “These cataracts affect the quality of vision and decrease contrast sensitivity, making it harder to read the newspaper,” adds Dr. Sikder. You don’t have to be a senior citizen to get an age-related cataract. However, since they’re usually small early on, you may not notice vision changes until after age 60.
- Congenital or pediatric cataracts. A congenital cataract is a cataract present at birth or developed shortly after during early childhood. A gene or a maternal illness during pregnancy—such as malnutrition, an infection or oxygen insufficiency—can cause congenital cataracts. A pediatric cataract, or cataract in children, is rare.
- Radiation cataracts. Exposure to radiation, such as ultraviolet rays from the sun and radiation treatments for cancers, can damage the eye lens and cause a cataract.
- Secondary cataracts. Also known as posterior capsule opacification, secondary cataracts are a common condition that occurs after cataract surgery. The thin membrane that holds the new lens in place can grow scar tissue and cloud your vision again. Laser treatment is common for secondary cataracts.
- Traumatic cataracts. Most common in young adults, traumatic cataracts may appear immediately after an injury or form many years later. Such damage can stem from perforation, blunt trauma, electric shock, ionizing radiation and chemical injuries.
How Common Are Cataracts?
Cataracts are quite common. In fact, they are the second most pervasive cause of age-related vision loss, accounting for 51% of the world’s blindness. Advancing age accounts for most cataracts, due to the natural degenerative effects of aging on cell structure.