Eye diseases are conditions that damage the structures of the eye and impair vision, ranging from common refractive errors like nearsightedness to serious conditions like glaucoma and macular degeneration. Globally, at least 2.2 billion people have some form of vision impairment, and for at least 1 billion of them, the problem could have been prevented or hasn’t been addressed yet. Here’s a breakdown of the most common eye diseases, what they do to your vision, and what to watch for.
Refractive Errors
Refractive errors are the most widespread eye conditions in the world. They occur when the shape of your eye prevents light from focusing correctly on the retina, the light-sensitive tissue at the back of your eye. There are three main types:
- Nearsightedness (myopia): The eyeball is too long from front to back, so light focuses in front of the retina instead of on it. Distant objects look blurry while close-up vision stays clear.
- Farsightedness (hyperopia): The eyeball is too short, causing light to focus behind the retina. Close objects are harder to see clearly.
- Astigmatism: The cornea or lens has an irregular shape, bending light unevenly as it enters the eye. This causes blurry or distorted vision at all distances.
All three are correctable with glasses, contact lenses, or laser surgery. They aren’t diseases in the traditional sense, but they’re often grouped with eye diseases because untreated refractive errors are one of the leading causes of vision impairment worldwide.
Cataracts
A cataract forms when proteins and fibers inside the eye’s lens break down and clump together, creating a cloudy area that blocks and scatters light before it can reach the retina. The result is progressively blurred vision, similar to looking through a fogged-up window.
Cataracts develop slowly, and early symptoms can be subtle. You might notice you need brighter light to read, or that colors appear faded or yellowish. Night driving becomes harder as halos and starbursts form around headlights and streetlights. Some people experience double vision in one eye or find themselves needing new glasses prescriptions more frequently than usual.
Aging is the primary cause, though diabetes, smoking, prolonged sun exposure, and long-term use of certain medications can accelerate the process. Cataract surgery, which replaces the clouded lens with a clear artificial one, is one of the most commonly performed operations in the world and has a high success rate.
Glaucoma
Glaucoma damages the optic nerve, which carries visual information from your eye to your brain. The damage is usually linked to elevated pressure inside the eye. Normal eye pressure ranges from 10 to 21 mmHg; anything above 21 is considered high, though some people develop glaucoma even at normal pressure levels.
The most common form, open-angle glaucoma, progresses so gradually that many people don’t notice vision loss until significant damage has occurred. It typically affects peripheral (side) vision first, leaving central vision intact until later stages. This is why glaucoma is often called the “silent thief of sight.” A less common form, angle-closure glaucoma, can come on suddenly with severe eye pain, headache, nausea, and blurred vision, requiring immediate treatment.
The nerve damage from glaucoma is irreversible, which makes early detection through routine eye exams critical. Treatment focuses on lowering eye pressure with drops, laser procedures, or surgery to slow or halt further damage.
Age-Related Macular Degeneration
Age-related macular degeneration (AMD) attacks the macula, the small central portion of the retina responsible for sharp, straight-ahead vision. Unlike glaucoma, AMD targets central vision while leaving side vision intact. Over time, you might struggle to read, recognize faces, or drive, even though you can still see objects in your periphery.
AMD comes in two forms. Dry AMD, the more common type, happens when the tissue in the macula thins and loses light-sensitive cells over time. It progresses slowly and may cause mild blurriness for years before becoming severe. In advanced cases, a blind spot forms in the center of your visual field.
Wet AMD is less common but more aggressive. It develops when abnormal blood vessels grow beneath the retina and leak fluid or blood, causing rapid damage to the macula. Dry AMD can progress into the wet form, which is why monitoring any changes in your central vision matters. Treatments for wet AMD, including eye injections that stop abnormal blood vessel growth, can slow the disease if caught early.
Diabetic Retinopathy
Diabetic retinopathy is a complication of diabetes that damages the blood vessels in the retina. Chronically high blood sugar weakens the walls of tiny retinal blood vessels, causing them to bulge, leak, or close off entirely. It’s a leading cause of blindness in working-age adults.
The disease progresses through stages. In the earliest phase, small bulges called microaneurysms appear in retinal blood vessels. These are often the first detectable sign, visible as tiny red dots during an eye exam, though you probably won’t notice any symptoms yourself. As the disease worsens, more vessels become damaged, and fluid and blood leak into the retina.
In the most advanced stage, called proliferative diabetic retinopathy, the retina is so starved of oxygen that the body grows new blood vessels to compensate. These new vessels are fragile and prone to bleeding, which can cause sudden, severe vision loss. Tight blood sugar control significantly reduces the risk of developing retinopathy and slows its progression if it’s already present.
Dry Eye Disease
Your eyes stay comfortable and clear thanks to a tear film made of three layers: an outer oily layer, a watery middle layer, and an inner mucus layer. Dry eye disease happens when this system breaks down, either because you don’t produce enough tears or because your tears evaporate too quickly.
The evaporative type is more common and is usually caused by clogged oil glands along the edges of the eyelids. Without enough oil in the tear film, tears dry up too fast. People with skin conditions like rosacea are more prone to this. Spending long hours reading or staring at a screen also contributes, because you blink less often during focused tasks, giving tears more time to evaporate. Wind, dry air, and smoke make things worse.
The other type, reduced tear production, becomes more common with age. Autoimmune conditions, antihistamines, antidepressants, blood pressure medications, and even contact lens use can all decrease the watery component of tears. Symptoms include stinging, burning, grittiness, blurred vision, and, paradoxically, watery eyes as the surface irritation triggers reflex tearing. Artificial tears help in mild cases, while more persistent dry eye may need treatments that address the underlying cause.
Warning Signs That Need Urgent Attention
Most eye diseases develop gradually, but some symptoms signal an emergency. Seek immediate care if you experience sudden vision loss or a sudden change in vision, severe eye pain accompanied by a headache or sensitivity to light, nausea or vomiting alongside eye symptoms, sudden halos around lights, or blood or pus coming from the eye. A chemical splash or foreign object in the eye also requires emergency treatment. These symptoms can indicate conditions like acute glaucoma, retinal detachment, or infection that cause permanent damage without prompt intervention.
Recommended Eye Exam Schedule
Many serious eye diseases cause no symptoms in their early stages, which makes routine exams the best defense. The American Academy of Ophthalmology recommends that children have their eyes assessed during newborn checkups and at routine visits, with formal vision testing starting around age 3. School-age children should be screened every one to two years.
Adults with no symptoms or risk factors should get a baseline comprehensive eye exam at age 40. From 40 to 54, exams every two to four years are sufficient. Between 55 and 64, the interval tightens to every one to three years. After 65, an exam every one to two years is recommended even if your vision feels fine. If you have diabetes, a family history of glaucoma, or other risk factors, your eye doctor will likely recommend more frequent visits.