A cataract is a clouding of the natural lens inside your eye that gradually blurs your vision. The lens sits behind your iris (the colored part of your eye) and works like a camera lens, focusing light onto the retina at the back of your eye. When proteins inside that lens clump together, they scatter light instead of letting it pass through cleanly, and your vision becomes hazy, dim, or washed out. Cataracts are the most common cause of blindness worldwide, affecting roughly 100 million people globally as of 2021, more than double the number in 1990.
What Happens Inside the Lens
Your eye’s lens is made almost entirely of water and specialized proteins called crystallins. These proteins are arranged in precise, tightly packed layers that keep the lens transparent. Unlike most cells in your body, the fiber cells at the center of the lens have no blood supply and almost no ability to repair or replace damaged proteins. The crystallins you’re born with are largely the same ones you carry for life.
Over decades, those proteins accumulate chemical damage: small changes to their structure from oxidation, sugar exposure, and ultraviolet light. As damage builds, proteins begin to partially unfold, exposing sticky regions that are normally tucked away inside. The lens has a built-in defense system, a chaperone protein called alpha-crystallin, that latches onto these misfolded proteins and prevents them from sticking to each other. But alpha-crystallin is a finite resource. Once it’s overwhelmed and used up, damaged proteins begin clumping into larger and larger clusters. These clusters scatter incoming light instead of transmitting it, and the lens turns opaque.
Common Types of Cataracts
Not all cataracts form in the same part of the lens, and where they develop determines which symptoms you notice first.
Nuclear Cataracts
These form in the center (nucleus) of the lens and are the most common age-related type. As the nucleus hardens and yellows, it changes how the lens bends light. In early stages, this shift can actually improve your near vision temporarily, a phenomenon sometimes called “second sight.” You might find you can read without glasses for a while. As the cataract progresses, though, distance vision worsens and colors take on a brownish tint.
Cortical Cataracts
These start as white, wedge-shaped opacities in the outer layer of the lens and grow inward like spokes on a wheel. Cortical cataracts tend to cause significant glare, making it hard to see in bright sunlight or under oncoming headlights. They grow slowly and are especially common in people with diabetes, where they sometimes appear as snowflake-like opacities in younger patients.
Posterior Subcapsular Cataracts
These develop on the back surface of the lens, right in the path where light is most concentrated. Because of that location, even a small opacity can have a large effect on vision. They tend to interfere with both reading and distance vision and cause pronounced difficulty in bright light. This type is more common in people who use corticosteroid medications long-term, those who’ve had radiation treatment near the eyes, and people with chronic eye inflammation.
Symptoms and How They Progress
Cataracts typically develop so gradually that you may not notice changes at first. Early signs often include needing brighter light to read, colors appearing faded or yellowish, and a general sense that your vision is slightly hazy. As the cataract grows, more specific symptoms appear:
- Glare sensitivity: Bright lights become uncomfortable, and oncoming headlights at night may feel blinding.
- Halos or starbursts: You see rings or radiating lines around lights, especially at night.
- Frequent prescription changes: Your glasses or contact lens prescription shifts more often than it used to.
- Double vision in one eye: A cataract can split light within a single eye, creating a ghost image even when the other eye is closed.
- Poor night vision: Driving after dark becomes increasingly difficult.
These symptoms can overlap with other eye conditions, so a change in vision always warrants an eye exam rather than an assumption.
What Increases Your Risk
Age is the dominant risk factor. Most cataracts develop after age 60, though they can begin forming much earlier. Beyond aging, several factors accelerate protein damage in the lens.
Diabetes is one of the strongest. Elevated blood sugar triggers a chemical pathway in the lens that creates a sugar alcohol called sorbitol. Sorbitol draws water into the lens, disrupting its structure, and generates free radicals that damage crystallin proteins. Both the duration of diabetes and how well blood sugar is controlled (measured by HbA1c) significantly affect cataract risk.
Ultraviolet light exposure is another well-established contributor. UV radiation directly damages lens proteins through oxidation, which is why wearing sunglasses that block UV-A and UV-B rays is one of the most practical protective steps you can take. Smoking, heavy alcohol use, and eye injuries also raise your risk. Long-term use of corticosteroid medications, whether oral, inhaled, or eye drops, is particularly associated with posterior subcapsular cataracts.
How Cataracts Are Diagnosed
An eye doctor can detect cataracts during a routine exam, often before you notice any symptoms. The key tool is a slit lamp, a specialized microscope that shines a thin, bright beam of light into your eye. This lets the doctor see the lens in fine detail and identify where opacities are forming. A standard vision chart test measures how much your visual sharpness has changed. Your eye doctor will also check the pressure inside your eye and examine the retina and optic nerve to rule out other conditions that could be affecting your sight.
Many doctors also ask you to fill out a questionnaire about how your vision affects daily activities like reading, driving, and recognizing faces. This functional assessment plays a major role in deciding whether and when to consider surgery, because the threshold isn’t a specific test result. It’s whether the cataract is interfering with your life.
Surgery: What to Expect
There is no medication, eye drop, or exercise that can reverse a cataract once it forms. Surgery is the only treatment, and it’s one of the most commonly performed procedures in the world.
The standard technique, called phacoemulsification, uses an ultrasonic probe about the width of a pen tip. Your surgeon makes a tiny incision in the cornea, typically between 2.2 and 3.2 millimeters wide. Through this opening, the probe vibrates at ultrasonic frequencies, breaking the clouded lens into small fragments that are suctioned out. The entire natural lens is removed from inside its thin capsular bag, which stays in place to hold the artificial replacement lens.
The procedure is done under local anesthesia, usually just numbing eye drops, and takes roughly 15 to 30 minutes. Most people go home the same day. Vision often begins to clear within a day or two, though full healing takes several weeks. You’ll use prescription eye drops during recovery to prevent infection and reduce inflammation.
Cataract surgery produces significant improvements in visual sharpness for the vast majority of patients. One common long-term side effect is posterior capsule opacification, where the capsular bag that holds the new lens becomes cloudy over time, occurring in roughly 12% of cases. This is easily treated with a quick, painless laser procedure in the office.
Choosing a Replacement Lens
When your clouded natural lens is removed, it’s replaced with a clear artificial lens called an intraocular lens (IOL). The type you choose determines how much you’ll rely on glasses after surgery.
Monofocal lenses are the most widely used. They provide sharp vision at one set distance, usually far away, meaning you’ll still need reading glasses for close-up tasks. These are typically covered by insurance and work well for most people.
Multifocal lenses have different focusing zones built into the same lens, allowing clear vision at near, intermediate, and far distances. They significantly reduce the need for glasses but can sometimes cause glare or halos around lights at night. Extended depth of focus lenses take a slightly different approach, stretching one focal point across a wider range rather than creating distinct zones. This produces smoother transitions between distances, particularly from far to intermediate (like a computer screen).
Toric lenses are designed specifically for people with astigmatism, correcting the uneven curvature of the cornea that causes blurred or distorted vision. Light adjustable lenses are a newer option that can be fine-tuned after surgery using a special UV light once the eye has healed, allowing your doctor to customize your prescription post-operatively.
Lowering Your Risk
You can’t fully prevent age-related cataracts, but you can slow the process. Wearing UV-blocking sunglasses outdoors is the simplest step, reducing the cumulative light damage that degrades lens proteins over decades. If you smoke, quitting removes one of the more significant modifiable risk factors. If you have diabetes, keeping blood sugar well controlled directly reduces the chemical stress on your lens.
Diet plays a role as well. Lutein and zeaxanthin, two pigments found in leafy greens, eggs, and corn, accumulate in the eye where they act as natural filters for blue light and neutralize damaging free radicals. Clinical trials have found that supplementing these nutrients has a protective effect against light-induced damage to the lens and retina. Notably, beta-carotene (the pigment in carrots) does not provide the same protection because it doesn’t pass into the eye in meaningful amounts, and high-dose supplementation may carry health risks of its own.
Regular eye exams remain important even if your vision seems fine. Cataracts can be detected early, tracked over time, and addressed when they begin to affect what matters to you, whether that’s reading, night driving, or simply seeing the world in sharp focus.