Cataracts form when proteins inside the lens of your eye clump together and block light from passing through clearly. This process can be triggered by aging, disease, injury, medications, and lifestyle factors. While age is the most common driver, understanding the full range of causes helps explain why some people develop cataracts decades earlier than others.
What Happens Inside the Lens
Your eye’s lens is made mostly of water and specialized proteins called crystallins. These proteins are arranged with extraordinary precision, packed tightly enough to stay transparent while still bending light onto the back of your eye. Unlike most cells in your body, the proteins in the center of the lens are never replaced. The crystallins you’re born with are the same ones you’ll have at 80.
Over a lifetime, these proteins accumulate damage from UV light, metabolic byproducts, and simple chemical wear. When crystallins lose their shape, they expose sticky surfaces that were previously tucked inside the molecule. These exposed surfaces latch onto neighboring proteins, forming clumps that scatter light instead of transmitting it. The process can follow several different pathways: proteins may form tangled fibers, amorphous blobs, or chains linked by chemical bonds between sulfur-containing parts of the molecule. In all cases, the result is the same. Patches of the lens turn cloudy, and vision gradually blurs.
The lens has a built-in defense system. Small chaperone proteins (a type of crystallin themselves) bind to damaged proteins and keep them from clumping. But this protection has a finite capacity. Once the chaperones are overwhelmed, aggregation accelerates. A rare genetic mutation illustrates this dramatically: one variant of a key crystallin protein uses up a lifetime’s worth of chaperone capacity in just a few years, causing cataracts in childhood.
Aging: The Most Common Cause
Most cataracts are age-related. By 80, more than half of all Americans either have a cataract or have had surgery to remove one. The lens slowly yellows and stiffens over decades as proteins accumulate oxidative damage and cross-link with each other. Dehydration within the lens also plays a role, disrupting the water layer around proteins and pushing them into irreversible contact with one another.
Age-related cataracts tend to develop in one of three zones of the lens. Nuclear cataracts form in the center and cause a gradual yellowing of vision. Cortical cataracts start as white, wedge-shaped streaks around the edges. Posterior subcapsular cataracts develop at the back surface and often cause glare and difficulty reading. You can develop more than one type at the same time, and each eye can progress at a different rate.
Diabetes and High Blood Sugar
People with diabetes develop cataracts earlier and more frequently than the general population. The mechanism is well understood. When blood sugar is consistently high, the normal glucose-processing pathway in lens cells becomes overloaded. Excess glucose gets diverted into an alternate route called the polyol pathway, where it’s converted into a sugar alcohol called sorbitol.
Sorbitol creates a two-pronged problem. First, it can’t cross cell membranes, so it accumulates inside lens cells and draws in water through osmosis, causing the cells to swell. Second, the chemical reactions that produce sorbitol consume a molecule the lens needs to regenerate its main antioxidant, glutathione. With less glutathione available, lens proteins are left exposed to oxidative damage. The same pathway also generates reactive oxygen species directly, compounding the stress. Over time, this combination of swelling and oxidation disrupts the fiber cells that make up the lens, leading to clouding.
Steroid Medications
Long-term use of corticosteroids is one of the most well-documented medication-related causes of cataracts. Both oral and inhaled steroids carry this risk, and it increases with higher doses and longer treatment courses. The type of cataract steroids produce is distinctive: a posterior subcapsular cataract, which forms at the back of the lens and tends to interfere with reading vision and cause halos around lights.
If you’re on corticosteroids for conditions like asthma, autoimmune disease, or organ transplant, regular eye exams can catch early changes before they affect your daily life. The risk doesn’t disappear immediately after stopping the medication, since the lens changes that have already occurred are permanent.
UV Light Exposure
Ultraviolet B radiation, the same wavelengths responsible for sunburn, damages lens proteins directly. UVB (wavelengths between 290 and 320 nanometers) triggers oxidative stress in lens cells and can push crystallin proteins into the same clumping process that happens with aging, just faster. Studies of outdoor workers and populations near the equator consistently show higher rates of cortical cataracts.
Sunglasses that block 99 to 100 percent of UVA and UVB rays are the most practical defense. Wide-brimmed hats help too. Cumulative exposure matters most, so starting these habits early in life has the greatest payoff.
Eye Injuries and Surgery
A direct blow to the eye or a penetrating injury can cause a cataract to form within minutes, months, or even years later, depending on the severity. When blunt force hits the eye, it sends a shockwave through the lens that can damage the thin capsule surrounding it or disrupt the cells beneath. If the capsule is breached, water rushes in and the lens can turn white within hours. If the capsule stays intact but the underlying cells are damaged, a characteristic rosette or star-shaped opacity develops over time.
Eye surgery itself can also trigger cataracts. After vitrectomy, a procedure that removes the gel inside the eye, roughly 80 percent of patients develop a visually significant cataract within two years. The change in the eye’s internal environment, particularly increased oxygen exposure to the lens, accelerates protein damage. Surgeons often plan for this possibility when recommending vitrectomy.
Smoking
Cigarette smoke delivers a concentrated dose of oxidative chemicals directly to body tissues, and the lens is not spared. Compounds like cadmium and isocyanate found in cigarette smoke can damage lens proteins both structurally and chemically. The relationship follows a clear dose-response pattern: the more cigarettes and the more years of smoking, the higher the risk of nuclear cataracts. People who smoke 20 or more cigarettes a day have a substantially higher risk than lighter smokers, who in turn have a higher risk than nonsmokers.
Quitting reduces the ongoing damage, though it doesn’t reverse clouding that has already occurred. Former smokers still carry elevated risk for years after stopping, but the trajectory improves compared to continuing.
Genetics and Congenital Cataracts
Some cataracts are present at birth or develop in early childhood due to inherited gene mutations. These congenital cataracts affect the proteins that make up the lens, the gap junctions that allow lens cells to communicate, or the membrane proteins that maintain lens structure. Autosomal dominant inheritance, where a single copy of the mutated gene from one parent is enough to cause the condition, accounts for about 44 percent of families with bilateral congenital cataracts.
Dozens of different genes have been linked to congenital cataracts. Some mutations cause channels between lens cells to become overactive, while others shut them down. Either extreme disrupts the tightly regulated internal environment the lens needs to stay clear. In many cases, surgical removal in infancy is necessary to prevent permanent vision loss from the brain never learning to process images from the affected eye.
Other Contributing Factors
Several additional factors raise cataract risk. Heavy alcohol use increases oxidative stress throughout the body, including the lens. Obesity and metabolic syndrome are associated with earlier onset, likely through the same blood sugar and inflammatory pathways involved in diabetic cataracts. Air pollution is an emerging risk factor, with higher cataract burdens documented in regions with poor air quality. Globally, South Asia and sub-Saharan Africa carry the heaviest cataract burden, driven by a combination of limited surgical access, high UV exposure, and metabolic disease.
Women develop cataracts at higher rates than men across all populations studied, a pattern that persists even after accounting for longer life expectancy. Hormonal differences, particularly the drop in estrogen after menopause, may reduce antioxidant protection in the lens, though the exact mechanism is still being clarified.
Can Diet Slow the Process?
Diets rich in fruits and vegetables are consistently linked to lower cataract risk in observational studies, likely because of their antioxidant content. Lutein and zeaxanthin, two pigments concentrated in leafy greens and egg yolks, accumulate in the lens and may help filter damaging light and neutralize free radicals. In the large AREDS2 clinical trial, participants who had the lowest dietary intake of these nutrients and then took supplements (10 mg lutein and 2 mg zeaxanthin daily) were 32 percent less likely to need cataract surgery compared to those who didn’t supplement. However, among participants who already ate adequate amounts, supplementation made no significant difference.
The practical takeaway: a diet consistently rich in colorful vegetables, particularly spinach, kale, and other dark leafy greens, provides the strongest nutritional foundation for lens health. Supplements may help fill a gap if your diet is lacking, but they don’t override the effects of aging, UV exposure, or uncontrolled blood sugar.