Cataracts form when proteins in the lens of your eye clump together and block light from passing through clearly. More than 82 million people worldwide were living with cataracts as of 2021, up from about 33 million in 1990. While aging is the most common trigger, cataracts can also result from diabetes, eye injuries, certain medications, and prolonged sun exposure.
How the Lens Loses Its Clarity
Your eye’s lens is made mostly of water and specialized proteins called crystallins, arranged in a precise pattern that keeps the lens transparent. These proteins need to stay properly folded and evenly distributed to let light pass through. Over a lifetime, the crystallins accumulate damage from oxidation, UV light, and normal metabolic wear. When damaged proteins unfold, they expose sticky surfaces that normally stay hidden inside the molecule. These exposed surfaces latch onto neighboring proteins, forming clumps that scatter light instead of transmitting it.
The process is gradual. Small clusters of misfolded proteins grow into larger aggregates, and the once-clear lens develops cloudy patches. In some cases, abnormal chemical bonds form between proteins, locking them into insoluble masses. The lens has no blood supply and can’t shed old cells the way skin or blood does, so damaged proteins simply accumulate year after year with no way to be cleared out.
Why Age Is the Biggest Risk Factor
Most cataracts develop after age 60, and the reason is cumulative. Decades of oxygen exposure, UV light, and metabolic byproducts steadily degrade the lens proteins. The lens also continues growing throughout life, adding new fiber cells on the outside while compressing older cells toward the center. This lifelong compaction makes the nucleus of the lens progressively denser and more yellow-brown over time.
Not all age-related cataracts are the same. The three main types have distinct patterns and somewhat different risk profiles. Nuclear cataracts form in the center of the lens and are strongly linked to smoking. Cortical cataracts develop in the outer layer and are closely tied to diabetes. Posterior subcapsular cataracts grow on the back surface of the lens and are associated with both diabetes and corticosteroid use. Lower socioeconomic status appears to increase risk across all three types, likely reflecting a combination of less access to eye care, poorer nutrition, and greater occupational exposure to hazards.
How Diabetes Accelerates the Process
People with diabetes face a significantly higher risk of cataracts, particularly cortical and posterior subcapsular types. The mechanism is tied directly to high blood sugar. When glucose levels in the blood are elevated, excess glucose enters the lens. An enzyme in the lens converts that glucose into a sugar alcohol called sorbitol, which the lens cells can’t easily push back out.
Sorbitol acts like a sponge, pulling water into the lens cells. This causes the cells to swell and disrupts the orderly arrangement of fibers that keeps the lens clear. At the same time, the chemical reaction that produces sorbitol uses up a molecule the lens needs to maintain its antioxidant defenses. With those defenses weakened, oxidative damage to lens proteins accelerates. The combination of swelling and oxidative stress can cause cataracts to develop earlier and progress faster in people with poorly controlled blood sugar.
UV Light and Sun Exposure
Ultraviolet radiation, particularly UV-B wavelengths around 300 nanometers, damages lens proteins through a photochemical chain reaction. When UV light hits the lens, it alters the structure of specific amino acids in crystallin proteins. One of these altered molecules becomes a potent photosensitizer, meaning it absorbs even more UV energy and passes that energy along to oxygen molecules, generating harmful reactive oxygen species like superoxide and hydrogen peroxide directly inside the lens.
This effect compounds with age. Older lenses already contain higher baseline levels of these photosensitized molecules, so they generate significantly more reactive oxygen species from the same amount of sunlight. This is one reason why cumulative sun exposure over a lifetime matters more than any single episode. Wearing sunglasses that block UV-A and UV-B rays reduces the dose of ultraviolet energy reaching the lens.
Medications That Cause Cataracts
Corticosteroids are the medication most clearly linked to cataract formation. Both oral and inhaled steroids can cause posterior subcapsular cataracts, the type that grows on the back surface of the lens and tends to interfere with reading vision and cause glare. The risk correlates with both the dose and the duration of use, and it applies across all delivery methods: pills, eye drops, inhalers, and injections.
Steroid-related cataracts are especially notable in younger patients, including children and adolescents being treated for asthma, autoimmune conditions, or organ transplants. If you take corticosteroids regularly, periodic eye exams can catch early lens changes before they affect your vision significantly.
Eye Injuries and Physical Trauma
A cataract can form after a blow to the eye, a puncture wound, a chemical splash, or exposure to radiation or electric shock. The timeline varies enormously depending on what happened. If a sharp object pierces the eye and reaches the lens capsule (the thin membrane surrounding the lens), the lens can cloud over within minutes to hours. The size of the opening matters: a large tear in the capsule can turn the entire lens opaque, while a small puncture may produce only a localized cloudy spot.
Blunt force trauma, like being hit by a ball or a fist, works differently. The impact sends a shockwave through the eye that can disrupt lens fibers without actually breaking through the capsule. These cataracts often develop a distinctive rosette or flower-shaped pattern. Some appear soon after the injury, but concussion cataracts can take months or years to become noticeable, progressing slowly as the disrupted fibers gradually lose transparency. Chemical burns alter the composition of the lens fibers directly, while electric shock can produce diffuse milky-white clouding or scattered snowflake-like opacities.
Smoking and Other Lifestyle Factors
Cigarette smoking is one of the strongest modifiable risk factors for nuclear cataracts, the type that forms in the center of the lens. Tobacco smoke delivers a heavy load of free radicals and depletes antioxidants in the body, including in the lens itself. The association is specific: smoking raises nuclear cataract risk but does not appear to independently increase the risk of cortical or posterior subcapsular types.
Lower body mass index has been linked to a higher risk of cortical cataracts in some populations, though the reasons aren’t fully understood. It may reflect nutritional deficiencies that compromise the lens’s antioxidant defenses. Occupations involving outdoor labor or factory work are associated with higher cataract rates across all types, likely because of greater UV exposure, chemical contact, or both.
Can Antioxidants Prevent Cataracts?
Given that oxidative damage plays a central role in cataract formation, it seems logical that antioxidant supplements might help. But the clinical evidence has been disappointing. The Antioxidants in Prevention of Cataracts Study, a five-year randomized controlled trial conducted in South India, tested daily supplements of vitamin C (500 mg), vitamin E (400 IU), and beta-carotene (25,000 IU) against a placebo. There was no difference in cataract progression between the two groups.
This result is particularly striking because the study population had low dietary antioxidant intake, meaning they were the people most likely to benefit if supplementation worked. The researchers concluded that these three antioxidants, taken in isolation, do not influence cataract progression. Some observational studies have suggested that other nutrients like lutein and zeaxanthin (found in leafy greens and eggs) may play a protective role, but these have not been confirmed in rigorous clinical trials. A diet rich in fruits and vegetables is generally good for eye health, but no supplement has been proven to prevent or slow cataracts.
Regional Differences in Cataract Rates
Cataracts are not distributed evenly around the world. South Asia has the highest age-adjusted prevalence rate, roughly ten times higher than high-income regions like Japan or North America. This disparity reflects a combination of intense UV exposure, higher diabetes rates, limited access to surgical care, nutritional factors, and occupational hazards. In wealthier countries, cataracts still develop at high rates in older adults, but they are typically removed surgically before causing severe vision loss, keeping the measured burden of disease lower.