Cataracts affect the lens, a small transparent structure sitting just behind the colored part of your eye (the iris) and your pupil. The lens is roughly the size and shape of an M&M candy, and its job is to focus incoming light onto the retina at the back of the eye, where images are formed. When a cataract develops, proteins inside this lens clump together and create cloudy patches that scatter light instead of transmitting it cleanly. The result is blurred, hazy, or washed-out vision that worsens over time.
How the Lens Works
The lens is one of two structures responsible for bending light as it enters your eye, the other being the cornea at the very front. What makes the lens unique is its ability to change shape. Tiny muscles surrounding it contract and relax to make the lens thicker or thinner, shifting its focal point so you can see things clearly whether they’re up close or far away. This is why reading becomes harder as cataracts progress: the lens can no longer transmit or focus light the way it should.
The lens itself has four layers. On the outside is the capsule, a thin elastic membrane that holds everything in place. Beneath that sits a layer of cells called the epithelium. The bulk of the lens is made up of two zones: the cortex (the outer portion) and the nucleus (the dense center). Different types of cataracts form in different zones, which is why not all cataracts look or behave the same way.
What Goes Wrong at the Protein Level
The lens is packed with specialized proteins called crystallins, arranged in a precise pattern that keeps the tissue perfectly clear. These proteins are some of the longest-lived in your entire body. The ones in the center of the lens have been there since before you were born, and they never get replaced. Over decades, they accumulate damage from oxidation, UV exposure, and normal metabolic wear. This damage causes the protein chains to partially unfold and expose sticky surfaces that were originally tucked away inside.
In a younger lens, a built-in chaperone system catches these damaged proteins and keeps them from sticking together. But over time this chaperone system becomes overwhelmed. Once it’s saturated, damaged crystallins begin clumping into large aggregates. These clumps are too big to transmit light cleanly. Instead, they scatter it in all directions, creating the characteristic cloudiness of a cataract.
Three Types Based on Location in the Lens
Cataracts are classified by where in the lens they form, and each type has a distinct pattern of vision loss.
- Nuclear cataracts form in the center of the lens. They’re the most common age-related type. The nucleus gradually turns yellow, then brown, causing colors to look faded and overall vision to become increasingly dim. In early stages, a nuclear cataract can temporarily improve near vision (sometimes called “second sight”) because the hardening nucleus changes the lens’s focusing power. This improvement doesn’t last.
- Cortical cataracts develop in the outer layer surrounding the nucleus. They start as white, wedge-shaped streaks at the edges of the lens and slowly work inward. Because the opacities sit off-center at first, you may notice glare and difficulty with contrast before your central vision drops. Cortical cataracts tend to grow slowly, though in advanced cases the entire lens can appear white.
- Posterior subcapsular cataracts form on the back surface of the lens, just inside the capsule. They sit right in the path of light heading toward the retina, so even a small opacity can cause noticeable symptoms. This type tends to grow faster than the others and is especially common in people who have used corticosteroid medications long-term or who have diabetes. It typically causes trouble with reading and significant glare from headlights or bright sunlight.
How Cataracts Change Your Vision
Early on, a cataract may cloud only a tiny portion of the lens, and you might not notice anything at all. As the cloudy area expands, it scatters more of the light passing through. Instead of landing on the retina as a sharp, focused image, light arrives diffused. This produces the blurry, foggy quality people describe.
But blurriness isn’t the only symptom. The scattered light also creates stray light inside the eye, which is responsible for glare, halos around bright lights, and a general loss of contrast. Colors can appear duller or yellowed because the browning lens acts like a tinted filter. Night driving often becomes difficult before daytime vision is noticeably affected, because headlights and streetlights generate intense glare against a dark background. Research on stray light shows it can seriously impair visual function even when a standard eye chart test still looks relatively normal.
When Cataracts Affect Other Parts of the Eye
A cataract that’s left untreated for a long time can cause problems beyond the lens itself. As the lens continues to swell or break down, it can raise the pressure inside the eye, a condition called lens-induced glaucoma. This happens through several different mechanisms depending on how the lens is changing.
A swollen, enlarged lens can physically push the iris forward, narrowing the drainage angle where fluid normally exits the eye. This creates a sudden spike in eye pressure that causes pain, corneal swelling, and rapid vision loss. In very advanced cataracts, proteins can leak through tiny defects in the lens capsule and clog the eye’s drainage system, triggering a different form of pressure buildup. Either scenario is an emergency that can permanently damage the optic nerve and the retinal cells it connects to if the pressure isn’t brought down quickly.
What Happens During Treatment
The only way to remove a cataract is surgery. No eye drops, supplements, or exercises can reverse the protein clumping once it’s happened. During the procedure, the clouded natural lens is broken up and removed, then replaced with a clear artificial lens that sits in the same spot. The artificial lens is permanent and doesn’t develop cataracts.
Modern replacement lenses come in several designs. Standard single-focus lenses correct vision at one distance, usually far, meaning you’ll likely still need reading glasses. Extended-depth-of-focus lenses stretch your range of clear vision so you can handle more tasks without glasses. Trifocal lenses aim to cover near, intermediate, and distance vision. Your eye surgeon will recommend a lens type based on your lifestyle, the health of the rest of your eye, and how much uncorrected range you want after surgery.
The procedure itself typically takes 15 to 20 minutes per eye and is done under local anesthesia. Most people notice clearer vision within a few days, though full healing takes several weeks. Cataract surgery is one of the most commonly performed operations in the world and carries a high success rate, but the timing is a personal decision based on how much your vision is affecting daily activities like driving, reading, or working.