Cataracts occur due to changes in the protein structure and water content of the crystalline lens. Normally, the crystalline lens is very clear, due to its highly ordered arrangement of specialized proteins and water. Many processes, however, may cause changes in these proteins, which result in loss of clarity of the lens.


By far the most common cause of cataract is aging. Almost everyone will develop some degree of cataract as they become older, with more than 70% of people over age 75 having some degree of these lens changes. As many older people with cataracts suffer a decline in vision, cataract surgery is often required to restore visual function. In fact, 1.3 million cataracts are surgically removed each year in the United States, making cataract surgery one of the most common surgical procedures in the United States today. The exact reason why cataracts commonly appear with age is not well understood by scientists. Nuclear Sclerosis and Cortical Spoke cataracts are commonly associated with aging.


Several medications can cause cataract with long-term use. The most common medications causing cataracts are corticosteroids; they are often referred to simply as “steroids.” Asthma and rheumatoid arthritis are two such diseases that often require long-term steroid use. Steroid associated cataracts are often Posterior Subcapsular cataracts. Long-term use of the eye medication pilocarpine can also cause cataracts to form.


Any severe injury to the eye can result in the formation of a traumatic cataract. These cataracts almost always form if a foreign object has penetrated the eye and directly damaged the lens. They can also form after severe blunt injury to the eye, in which the eye briefly collapses.

Prior Eye Surgery

Eye surgery for reasons other than cataract removal can occasionally result in the formation of a cataract. Rarely, this occurs due to damage of the crystalline lens during the surgery itself from instruments or lasers. Usually, however, cataracts may form slowly after eye surgery. Scientists believe this is due to an alteration in the way eye fluid moves within the eye after eye surgery is performed. Such alterations in eye fluid movement are common in retinal and glaucoma surgeries, and, as such, cataracts may occur after these procedures.

Congenital Cataracts

Congenital cataracts are present at birth and due to an abnormal formation of the lens while in the womb. Typically, these cataracts do not worsen with time, but occasionally can result in marked decreased vision for the infant. In such cases, babies undergo cataract surgery to allow them to see more normally as they age. Most congenital cataracts, however, do not cause significant decrease in vision and can be left in the eye without any problem.

Cataracts Associated with other Diseases

Several other bodily diseases can cause cataracts to form. Diabetes is the disease most commonly associated with cataracts. Diabetes associated cataracts typically look like age-related cataracts, but may form much sooner due to the diabetes. Some diabetic individuals need cataract surgery around 30-40 years old, rather than 60-70 years old, as is usual for age-related cataracts. Rare diseases, such as Wilson’s disease and myotonic dystrophy, are also associated with cataracts. Long-term eye inflammation, such as uveitis, may also cause cataracts to form.

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