Many things can make your eyesight worse, ranging from everyday habits like prolonged screen use and too little time outdoors to chronic health conditions like diabetes and high blood pressure. Some factors, like genetics, are out of your control. But many of the biggest drivers of declining vision are things you can actually change.
Too Much Close-Up Work, Too Little Sunlight
Spending long stretches focused on nearby objects is one of the strongest environmental drivers of worsening nearsightedness, especially in children. Reading or using a screen at a distance of less than 30 centimeters (about 12 inches) raises the odds of developing myopia by roughly 2.5 times. Continuous close work for more than 30 minutes without a break increases the risk by about 1.5 times. In children, prolonged screen time has been linked to a 4- to 8-fold increase in myopia risk.
What offsets this is surprisingly simple: going outside. It’s the outdoor light itself, not physical activity, that appears protective. Children who spend more than 40 minutes a day outdoors have significantly lower rates of nearsightedness, and outdoor time can even reduce the influence of other risk factors like having myopic parents. Experts have suggested a minimum of one hour of outdoor recess for schoolchildren, along with classrooms designed with large windows to maximize natural light exposure.
Screen Time and Digital Eye Strain
If your vision feels blurry after hours on a computer or phone, that’s digital eye strain. Symptoms include dry eyes, burning, headache, blurred vision, and difficulty shifting focus between distances. The prevalence among children has reached 50 to 60 percent in recent studies.
For adults, the good news is that digital eye strain is generally temporary. There is no strong evidence that screens cause permanent structural damage to adult eyes. The symptoms resolve once you rest. For children, however, the picture is different: heavy screen use has been linked to new-onset myopia and faster progression of existing nearsightedness. The developing eye appears more vulnerable to the sustained close focus that screens demand.
Genetics and Family History
Your genes set the baseline. A child with one nearsighted parent is about twice as likely to develop myopia. With two nearsighted parents, the risk jumps roughly fivefold. Studies comparing children of similar genetic backgrounds have found that those growing up in rural environments have lower myopia rates than those in urban, high-density areas, suggesting that environment and genetics interact. Education level also amplifies genetic risk: countries that increased mandatory school years saw corresponding rises in myopia prevalence.
Smoking
Smoking is one of the most damaging things you can do to your eyes. According to the FDA, smokers are two to three times more likely to develop cataracts, where the lens clouds over and blocks light from reaching the back of the eye. They are also up to four times more likely to develop age-related macular degeneration (AMD), which gradually destroys the central part of your visual field. AMD can eventually leave you unable to read, drive, or recognize faces. Both conditions are leading causes of vision loss worldwide.
Diabetes and High Blood Sugar
Chronically elevated blood sugar damages the tiny blood vessels that supply your retina, the light-sensitive tissue at the back of the eye. This condition, diabetic retinopathy, affects roughly 3.9 million people globally and is one of the top five causes of blindness. Retinal damage begins to appear once long-term blood sugar (HbA1c) rises above about 6.5 percent. Below 6.0 percent, the risk of diabetes-specific retinal changes is low. The damage is gradual. You may not notice symptoms until significant vision loss has already occurred, which is why regular eye exams matter if you have diabetes or prediabetes.
High Blood Pressure
Chronic high blood pressure quietly reshapes the blood vessels in your retina through a process called hypertensive retinopathy. It unfolds in stages. First, the small arteries in the eye constrict as they try to manage the increased pressure. If high blood pressure persists, the vessel walls physically thicken and stiffen, a change visible to an eye doctor as a copper or silver sheen along the arteries. In advanced stages, vessels leak, causing small hemorrhages and swelling in the retina that can blur your vision. These changes often develop over years without obvious symptoms.
UV Exposure
Ultraviolet light from the sun contributes to both cataract formation and retinal degeneration over time. The damage is cumulative, meaning years of unprotected sun exposure add up. Sunglasses that block 99 to 100 percent of UVA and UVB rays are the most practical protection. A wide-brimmed hat cuts exposure further. This is especially relevant if you spend significant time outdoors, live at high altitude, or work around reflective surfaces like water or snow.
Rubbing Your Eyes
Chronic, vigorous eye rubbing is a well-established risk factor for keratoconus, a condition where the cornea thins and bulges into a cone shape. As the cornea distorts, vision becomes increasingly blurry and difficult to correct with standard glasses. Keratoconus typically develops in the teens or twenties and worsens over time. The mechanical force of repeated rubbing appears to weaken the corneal structure. If you have allergies or dry eyes that make you rub frequently, treating the underlying itch or irritation is one of the most effective ways to protect your corneas.
Vitamin A Deficiency
Vitamin A is essential for the function of your retina, and severe deficiency can cause progressive, irreversible damage. The earliest sign is night blindness: difficulty seeing in dim light. As the deficiency deepens, the surface of the eye dries out, a condition called xerophthalmia. Without treatment, the cornea can ulcerate and, in the most severe cases, melt away entirely, leaving permanent scarring or total loss of the eye. This is rare in developed countries but remains a significant cause of childhood blindness in parts of South Asia and sub-Saharan Africa. Foods rich in vitamin A include liver, eggs, dairy, sweet potatoes, carrots, and dark leafy greens.
The Biggest Global Causes of Vision Loss
The World Health Organization ranks the leading causes of vision impairment and blindness worldwide as: uncorrected refractive errors (88.4 million people), cataracts (94 million), age-related macular degeneration (8 million), glaucoma (7.7 million), and diabetic retinopathy (3.9 million). Many of these conditions share overlapping risk factors. Smoking raises your risk of both cataracts and macular degeneration. Diabetes and high blood pressure both damage retinal blood vessels. And the single most common cause of blurry vision in the world, uncorrected refractive error, is driven by the interaction of genetics, close work, and insufficient outdoor time that starts in childhood.