Cataracts are caused by the clumping of proteins inside the lens of your eye, which gradually clouds your vision. Age is the primary driver, but diabetes, UV exposure, steroid medications, eye injuries, and certain genetic conditions can all trigger or accelerate the process. By the early 60s, roughly 3,000 to 3,700 out of every 100,000 people have cataracts, and the numbers climb steeply from there, with the highest burden falling on adults in their early 70s.
What Happens Inside the Lens
Your eye’s lens is made mostly of water and tightly organized proteins called crystallins. These proteins are some of the longest-lived in your body. They’re built to stay transparent for decades, but over time they begin to unfold and stick together. When one part of a crystallin molecule unfolds, it exposes sticky surfaces that were previously tucked away. Those exposed surfaces latch onto neighboring proteins, forming clumps that scatter light instead of letting it pass through cleanly.
The process is similar, at a molecular level, to what happens in some neurodegenerative diseases: proteins that were once neatly folded start to misbehave and aggregate. In the lens, the result isn’t nerve damage but a slow, progressive clouding. Oxidative damage from UV light, cigarette smoke, and normal metabolism accelerates this protein breakdown by generating reactive molecules that attack the crystallin structure directly. Your lens has built-in antioxidant defenses, but these weaken with age, leaving proteins increasingly vulnerable.
Age: The Biggest Risk Factor
Most cataracts are simply a consequence of living long enough. The proteins in your lens don’t get replaced the way skin or blood cells do. They accumulate damage year after year, and eventually the clumping becomes dense enough to interfere with vision. Women develop cataracts at slightly higher rates than men across every age group. Global data shows that in the 70 to 74 age range alone, approximately 7.1 million men and 9.6 million women are living with cataracts. By your 80s, the condition becomes more the rule than the exception.
How Diabetes Damages the Lens
High blood sugar doesn’t just affect your blood vessels and nerves. It also changes the chemistry inside your lens. When glucose levels stay elevated, the lens absorbs more sugar than it can process through its normal energy pathways. The excess glucose gets converted into sorbitol and fructose, two sugar alcohols that the lens can’t easily flush out.
These trapped sugars pull water into the lens through osmotic pressure, much like salt draws moisture into cured meat. The lens fibers swell, their internal scaffolding warps, and the once-clear tissue turns opaque. This is why people with poorly controlled diabetes often develop cataracts earlier and more aggressively than the general population. Keeping blood sugar well managed is one of the most effective ways to delay this process.
UV Light and Oxidative Stress
Ultraviolet radiation, particularly UV-B, is a well-established cause of lens damage. When UV-B hits the lens, it generates reactive oxygen species, unstable molecules that attack proteins, cell membranes, and DNA within lens cells. The lens has natural defense systems to neutralize these molecules, but chronic UV exposure gradually overwhelms them. Studies in mice have shown that animals missing a key protective enzyme develop significantly more light scattering in their lenses after UV-B exposure compared to normal animals.
Wearing sunglasses that block UV-A and UV-B is one of the simplest preventive steps you can take. This is especially important if you spend long hours outdoors or live at high altitude, where UV intensity is greater.
Steroid Medications
Long-term use of corticosteroids, whether as eye drops, oral pills, or inhaled forms, increases cataract risk. The relationship is dose-dependent: higher doses over longer periods carry more risk. Research from the American Academy of Ophthalmology found that patients using more than three drops daily of topical steroid eye drops had a cataract incidence rate 16 times higher than those using three drops or fewer. Among patients using two drops or fewer daily, the rate dropped to zero over the study period.
If you take steroids for conditions like asthma, arthritis, or inflammatory eye disease, your doctor likely already monitors your eye health. The risk doesn’t mean you should stop necessary medication, but it does mean regular eye exams become more important.
Eye Injuries
A hard blow to the eye, a puncture wound, or a chemical burn can all cause what’s known as a traumatic cataract. The mechanism is straightforward: physical force disrupts the delicate arrangement of lens fibers. If the outer capsule of the lens ruptures, fluid from the surrounding eye chamber rushes in and hydrates the fibers, causing them to swell and cloud. This can happen within minutes or hours of the injury, making traumatic cataracts far more sudden than the age-related kind. Even blunt impacts that don’t break the skin, like a ball or fist striking the eye, can cause cataracts that appear weeks or months later.
Smoking and Alcohol
Smoking accelerates cataract formation through multiple pathways. It floods the body with free radicals that deplete the lens’s antioxidant reserves, and it introduces toxic metals like cadmium and lead that accumulate in lens tissue over time. The more you smoke and the longer you smoke, the greater the risk.
Alcohol’s relationship with cataracts is more nuanced. Large cohort data from the UK Biobank and the EPIC-Norfolk study found that moderate drinkers (one to four times per week) actually had a 6% to 7% lower risk of needing cataract surgery compared to non-drinkers. Heavy drinkers, however, had a 5% to 6% higher risk than moderate drinkers. The takeaway isn’t that drinking prevents cataracts, but that heavy consumption adds measurable risk.
Cataracts Present at Birth
Not all cataracts develop with age. Congenital cataracts appear at birth or in early infancy and have a different set of causes. Infections passed from mother to baby during pregnancy are one major trigger, with rubella being the most well-known. Genetic conditions also play a significant role. Down syndrome, galactosemia (a disorder of sugar metabolism), and Lowe syndrome are among more than a dozen conditions linked to congenital cataracts. Some families carry inherited mutations that cause cataracts across generations without any associated syndrome.
Congenital cataracts require early detection because a clouded lens during infancy can permanently impair visual development if not treated promptly.
Nutrition and Prevention
Your diet influences how well your lens holds up over time. Vitamin C is the most consistently supported nutrient for cataract prevention. As a powerful antioxidant, it helps neutralize the reactive molecules that damage lens proteins. Higher dietary intake of vitamin C is associated with lower rates of age-related cataracts.
Lutein and zeaxanthin, pigments found in leafy greens, eggs, and corn, also show protective effects. A dose-response analysis found that consuming an additional 10 milligrams of lutein or zeaxanthin daily reduced cataract risk by 19%. Vitamin E’s role is less clear. Some studies suggest it protects against one type of cataract (nuclear) but not others, and the overall evidence remains mixed. Eating a diet rich in fruits, vegetables, and whole foods gives you the broadest protective benefit, rather than relying on any single supplement.
Secondary Cataracts After Surgery
Even after successful cataract surgery, 20% to 50% of adults develop a secondary clouding called posterior capsule opacification within two to five years. This isn’t a new cataract forming on a new lens. During surgery, the back wall of the lens capsule is left in place to support the artificial replacement lens. Cells left on that capsule can grow and cloud over, mimicking the blurred vision of the original cataract. In children, the rate approaches 100%. The fix is a quick, painless laser procedure that clears the clouded capsule in minutes, but knowing this possibility exists helps set realistic expectations after surgery.