Cataracts form when proteins inside the lens of your eye clump together and block light from passing through clearly. Over 100 million people worldwide have cataracts, and the condition is overwhelmingly concentrated in adults over 50. But aging isn’t the only cause. Diabetes, eye injuries, medications, UV exposure, and even genetics at birth can all cloud the lens.
What Happens Inside the Lens
Your eye’s lens is made mostly of water and tightly organized proteins called crystallins. These proteins are arranged in a precise, transparent structure that lets light pass through to the retina at the back of your eye. For this to work, the proteins need to stay perfectly folded and evenly distributed.
Over a lifetime, those proteins accumulate damage from UV light, oxidation, and normal chemical wear. The damaged proteins begin to unfold and expose sticky surfaces that were previously tucked away. Once exposed, these surfaces latch onto neighboring proteins, forming larger and larger clumps. Your lens has a built-in defense system: a protein called alpha-crystallin acts as a chaperone, grabbing misfolded proteins before they can stick together. But there’s a finite supply of this chaperone. Once it’s overwhelmed, damaged proteins clump freely into insoluble masses that scatter light instead of transmitting it. That scattering is what makes the lens look cloudy and your vision hazy.
Age-Related Cataracts
Aging is by far the most common reason cataracts develop. The lens has almost no ability to replace its oldest cells, so damage accumulates year after year with no reset. Reactive oxygen species, the same unstable molecules involved in broader aging, build up inside the lens through the activity of pro-oxidant enzymes. These molecules chemically alter proteins and fats in lens cells, triggering the clumping process described above. At the same time, the lens gradually loses its natural antioxidants, particularly glutathione and vitamin C, which normally neutralize those reactive molecules. The result is a slow tipping point: as antioxidant defenses decline and oxidative damage rises, the lens becomes progressively more opaque.
This process typically becomes noticeable after age 50. In 2020, roughly 94 million people aged 50 and older worldwide had blindness or visual impairment from cataracts. The global number of people living with cataracts rose from about 42 million in 1990 to over 100 million in 2021.
How Diabetes Leads to Cataracts
High blood sugar creates a separate pathway to lens clouding. When glucose levels stay elevated, the lens converts excess sugar into a substance called sorbitol through what’s known as the polyol pathway. Sorbitol doesn’t pass through the lens membrane easily, so it builds up inside. This trapped sorbitol draws water into the lens to balance the concentration, much like salt draws water through a membrane. The lens has pumps that try to compensate, but they eventually become overloaded. The result is swollen, waterlogged lens fibers that degenerate and turn opaque.
This is why people with poorly controlled diabetes often develop cataracts earlier than the general population. The process is driven directly by how high and how long blood sugar stays elevated.
UV Light and Sun Exposure
Ultraviolet B radiation, the same wavelength responsible for sunburns, damages the lens by triggering cell death in lens epithelial cells. UVB exposure causes these cells to self-destruct in a dose-dependent way: more exposure means more cell death. The radiation also disrupts the energy-producing structures within cells and generates reactive oxygen species that further damage lens proteins. Over years of cumulative exposure, this contributes to the same protein clumping that drives age-related cataracts.
Wearing sunglasses that block UVA and UVB rays is one of the most straightforward ways to slow this process. Hats with brims also reduce the amount of UV light reaching your eyes.
Eye Injuries and Trauma
A blow to the eye, a puncture wound, or even a strong concussion can cause a traumatic cataract. Blunt force transfers energy through the eye, disrupting lens fibers and potentially rupturing the lens capsule, the thin membrane that holds the lens in place. Once the capsule is breached, fluid rushes in and the lens proteins denature and coagulate, turning white and opaque.
The timeline varies dramatically. If the lens capsule is torn, clouding can appear within minutes to hours. In cases of blunt trauma without a capsule break, a cataract may develop slowly over months or even years. Some people don’t realize their eye injury caused a cataract until long after the original event.
Steroid Medications
Long-term use of corticosteroids is a well-established cause of cataracts, particularly a type that forms at the back of the lens. The risk depends on the total dose, how long you take the medication, and how it’s delivered. Oral steroids carry the highest risk, followed by topical eye drops, then inhaled forms.
In studies of children treated with oral steroids for kidney disease, about 18% developed steroid-related cataracts after an average of 4.3 years of treatment. For people using high-dose inhaled corticosteroids (common in severe asthma or COPD) for over 12 months, cataract rates approached 40%. Low-dose inhaled steroids showed no significant risk. If you take corticosteroids regularly for any condition, periodic eye exams can catch lens changes early.
Cataracts Present at Birth
Some babies are born with cataracts or develop them in early childhood. Congenital cataracts affect roughly 1 to 15 out of every 10,000 live births, with higher rates in developing countries. Over 100 genes have been linked to inherited cataracts, and mutations in just two types of proteins, crystallins and connexins, account for a large share of genetic cases. Connexin defects alone are responsible for about 20% of nonsyndromic congenital cataracts.
Congenital cataracts can also result from infections during pregnancy or metabolic disorders. In some cases, they appear alongside other eye abnormalities like an unusually small cornea. Because the same type of cataract can be caused by mutations in completely different genes, genetic testing is often needed to identify the specific cause.
Other Risk Factors
Heavy alcohol consumption modestly raises cataract risk. A study of Chinese adults found that drinking more than 280 grams of alcohol per week (roughly 20 standard drinks) was associated with a 21% higher risk compared to occasional drinkers. Interestingly, moderate drinking appeared to have a lower associated risk than either heavy drinking or complete abstinence, though this doesn’t mean drinking protects your eyes.
Smoking has long been suspected as a risk factor, though some recent studies have found no statistically significant link. The relationship may depend on the type of cataract and the population studied. Regardless, smoking accelerates oxidative damage throughout the body, including the lens.
Can Diet Slow Cataract Formation?
Lutein and zeaxanthin, two pigments found in leafy greens, eggs, and corn, concentrate in the eye and act as natural filters and antioxidants. A large clinical trial (AREDS2) tested whether supplementing with 10 mg of lutein and 2 mg of zeaxanthin daily could slow cataract progression. For people whose diets were already rich in these nutrients, supplements made no measurable difference. But for those with the lowest dietary intake, supplementation reduced the risk of progressing to cataract surgery by 32% and reduced severe cataracts by 36%.
The practical takeaway: if you rarely eat spinach, kale, collard greens, or eggs, either adding more of these foods or taking a lutein/zeaxanthin supplement may offer meaningful protection. If your diet already includes plenty of these foods, extra supplements are unlikely to help. Protecting your eyes from UV light and managing blood sugar if you have diabetes remain the most impactful preventive steps.