Cataracts are the leading cause of blindness worldwide, responsible for approximately 17 million cases of blindness in 2020, or about 40% of all global blindness. Refractive errors (nearsightedness, farsightedness, and astigmatism) follow closely, causing an estimated 88.4 million cases of distance vision impairment. Together, these two highly treatable conditions account for the majority of vision loss on the planet.
At least 2.2 billion people globally live with some form of vision impairment. What makes that number striking is how many of those cases could be corrected or prevented with interventions that already exist.
Cataracts: The Biggest Single Cause
A cataract is a clouding of the eye’s natural lens, which sits behind the pupil. As proteins in the lens break down with age, they clump together and block light from reaching the retina clearly. Vision gradually becomes blurry, faded, or washed out, like looking through a foggy window. Most cataracts develop after age 50, and the risk climbs steadily from there.
Cataract surgery, which replaces the clouded lens with an artificial one, is one of the most commonly performed surgeries in the world. It takes roughly 15 to 30 minutes, and most people notice dramatically improved vision within days. In high-income countries, cataract blindness is relatively rare because surgery is widely accessible. The burden falls disproportionately on low- and middle-income countries, where access to surgical care is limited. Women are affected more than men: about 60% of people blind from cataracts are female, likely due to longer life expectancy combined with less access to healthcare in many regions.
Uncorrected Refractive Errors
Refractive errors happen when the shape of the eye prevents light from focusing properly on the retina. The most common types are myopia (nearsightedness), hyperopia (farsightedness), and astigmatism. These conditions are correctable with glasses, contact lenses, or laser surgery. Yet an estimated 8 million people worldwide are blind and another 145 million have significant vision loss simply because they lack access to corrective lenses.
This makes uncorrected refractive error one of the most solvable vision problems in existence. A pair of glasses costing a few dollars can restore functional sight. The gap is almost entirely one of access, particularly in rural areas of sub-Saharan Africa, South Asia, and parts of Southeast Asia, where eye care professionals and optical services are scarce.
Glaucoma: The Leading Irreversible Cause
While cataracts and refractive errors can be fixed, glaucoma causes permanent damage. It affects about 7.7 million people with blindness globally, making it the second leading cause of blindness overall and the top cause of irreversible blindness. Around 3 million Americans have the condition.
Glaucoma damages the optic nerve, the cable that carries visual information from the eye to the brain. The most common form, open-angle glaucoma, involves a gradual buildup of pressure inside the eye. It typically starts by eroding peripheral (side) vision so slowly that many people don’t notice until significant damage has already occurred. By the time central vision is affected, a large portion of the nerve fibers may be permanently destroyed. There’s no way to restore vision already lost to glaucoma, but treatments that lower eye pressure (drops, laser procedures, or surgery) can slow or halt further damage if the condition is caught early. Regular eye exams are the only reliable way to detect it before symptoms appear.
Age-Related Macular Degeneration
Age-related macular degeneration, commonly called AMD, is the most common cause of irreversible blindness in older adults in developed countries. It affects one in eight people aged 60 or older and targets the macula, the small central area of the retina responsible for sharp, detailed vision. People with AMD may notice blurriness in the center of their visual field, difficulty reading, or distortion where straight lines appear wavy.
More than 200 million people worldwide are affected. AMD comes in two forms: a slow-progressing “dry” type that accounts for most cases, and a faster, more damaging “wet” type where abnormal blood vessels leak fluid beneath the retina. Treatments for wet AMD (injections that block blood vessel growth) can preserve vision but need to be administered regularly, sometimes monthly. Dry AMD has fewer treatment options, though nutritional supplements may slow progression in intermediate cases. Projections suggest that by 2050, over 9 million people will have AMD-related vision loss, driven largely by aging populations worldwide.
Diabetic Retinopathy Is Rising Fast
Diabetic retinopathy currently causes blindness in about 3.9 million people globally, placing it fifth among leading causes. But it’s growing faster than any other major cause of blindness. Between 1990 and 2021, the number of people blinded by diabetic retinopathy increased by 326%, and the trend is projected to continue through at least 2035.
The condition develops when consistently high blood sugar damages the tiny blood vessels in the retina. These vessels can swell, leak, or close off entirely. In advanced stages, the eye grows fragile new blood vessels that bleed easily, scarring the retina and potentially causing detachment. The explosion in cases tracks directly with the global rise in diabetes, fueled by aging populations, sedentary lifestyles, and dietary shifts toward processed foods. For people with diabetes, the most protective steps are keeping blood sugar and blood pressure well controlled and getting annual dilated eye exams, since early-stage retinopathy usually causes no symptoms.
Trachoma: The Infectious Threat
Trachoma is the leading infectious cause of blindness in the world. It’s caused by repeated bacterial infections that scar the inside of the eyelid over years, eventually turning the eyelashes inward so they scrape the cornea with every blink. This chronic abrasion clouds the cornea and destroys vision.
Unlike the other causes on this list, trachoma is concentrated in specific regions with limited access to clean water and sanitation, primarily in parts of Africa, Asia, and Central and South America. The good news is that global elimination efforts have made real progress. Mexico became the first country in the Americas to eliminate trachoma as a public health problem in 2017, and dozens of other countries have followed or are close behind. The strategy combines antibiotics, facial cleanliness education, and environmental improvements like better sanitation.
Why Most Blindness Is Preventable
The pattern across these conditions is striking: the two biggest causes of blindness, cataracts and refractive errors, are fully treatable with existing technology. Glaucoma and diabetic retinopathy can be managed effectively when detected early. Trachoma is being systematically eliminated. Even AMD, the hardest to treat, can be slowed in many cases. The primary barriers are not medical but structural: too few eye care providers in the regions that need them most, too little screening, and the cost of treatment falling on people who can’t afford it.
As global populations age and diabetes rates continue climbing, the total number of people living with vision loss is expected to grow substantially by mid-century. Population aging alone will drive increases in cataracts, glaucoma, AMD, and diabetic retinopathy simultaneously. Scaling up access to cataract surgery, distributing corrective lenses, and expanding diabetes screening in low-resource settings remain the highest-impact interventions available.