What Is a Cataract? - Definition, Symptoms & Surgery

Instructor: Catherine Konopka

Catherine has taught various college biology courses for 5 years at both 2-year and 4-year institutions. She has a Ph.D. in cell and molecular biology.

Did you know that you can be born with cataracts or develop it over time? In this lesson, you will learn about the eye condition and the surgery performed to correct it.

Having Cataracts Is Like Living in a Fog

Have you ever woken up one morning, looked out your window and could just barely see a nearby building because of the fog? How did it feel to drive on the highway when you could barely see the car in front of you? For people suffering from cataracts, it feels much like living in a fog. Before we talk about what causes cataracts, let's first review a little bit about the structure of the eye.

Structures of the Eye

When you look at something, light from the object enters into your eye. The light first passes through the outer fibrous layer called the cornea, then through a hole called the pupil, and finally through the lens before being detected on the retina at the back of the eyeball.

The cornea and lens in your eye are very similar to the lens on a camera. In a camera, the lens bends the light rays so they converge to form an in-focus image on the film (in the old days) or digital detector. In your eye, the cornea and lens bend the light rays so that they converge to form an in-focus image on your retina, which collects the image information and sends it to the brain.

Light from an object is bent by the cornea and lens so that it is focused on the retina.
Light from an object passes through the cornea and lens and is perceived on the retina

Cataract Is a Loss of Transparency

One important feature of the lens is that it is translucent, which means light passes through it instead of being absorbed or deflected. Light must pass through the lens, otherwise it would never get to the retina to be detected and we would never 'see' it. The special proteins inside the lens do not absorb or deflect light, thereby allowing it to pass through the lens. If these proteins deteriorate with age, they begin to clump together and become more opaque, which causes them to absorb or deflect light. This means less light from what you're looking at is getting to the correct spot on the retina. In other words, you are seeing less of the object or seeing it incorrectly.

The proteins in the cells of your eyes are like the proteins in an egg white. The proteins in a raw egg white are undamaged, clear and translucent. When you fry or boil an egg, you are damaging the proteins, which causes them to clump and become opaque. If you have cataracts, the proteins in your eyes become damaged, clump together and become opaque.

Symptoms of Cataracts

In rare instances, babies are born with cataracts. But in most cases, people develop cataracts with age. When a person is developing cataracts, they will first notice their vision becoming cloudy or blurry. Colors will become less vivid and be harder to distinguish. They may also have difficulty seeing at night and may need to have their prescription for glasses or contacts changed frequently. Finally, they may start seeing multiple images in one eye. All of these symptoms are due to the light from an object either being absorbed or deflected by the clumping, opaque proteins in the lens.

An eye with cataracts (on the left) will see an image as blurry, cloudy or with muted colors. After the damaged lens has been replaced during cataracts surgery (on the right) a persons vision is restored.
Cataracts causes vision to become blurry and cloudy

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