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A cataract is an extremely common, naturally occurring “clouding” or “yellowing” of the lens in your eye, which can cause foggy vision, as if you’re looking through a frosty or dirty window, among many other symptoms. Cataracts happen to most people as we get older, starting to develop in your 40s and 50s with symptoms becoming noticeable by age 60 to 70.

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Visual of 9 out of 10 people highlighted to illustrate 90% of people develop cataracts by age 65

But what is a cataract, exactly? To explain, we first need to understand a little better how the eye works. There are two structures, the cornea and the crystalline lens, that work together to focus light on the retina, which is the part of the eye that transmits information to the brain, allowing you to “see” images.

The cornea is the outer focusing structure, and the crystalline lens is the inner focusing structure. Light rays pass first through the cornea and then through the crystalline lens.

Diagram of a normal lens versus a cloudy lens from an eye cataract

Normal lens

Diagram of a normal lens versus a cloudy lens from an eye cataract

Eye with cataract

The cornea and crystalline lens focus incoming light by bending all the light rays to meet at a single point on the retina. From the retina, these light rays are sent as electrical pulses to the brain, where our mind “sees” a picture of what’s in front of us.

As we get older, cataracts cause the eye’s natural crystalline lens to become cloudy or yellow, preventing light rays from properly focusing inside the eye. Left untreated, cataracts cause vision to deteriorate over time.

How far along is my cataract?

In order to determine what stage your cataract is at, your physician will take photographs of your eye and examine both the clouding and the yellowing of the lens within a very specific area called “the grading region.”

The Grading Region

Your physician will then compare your photographs with photographs of healthy eyes and assign a grade based on the severity of the cataract in the image. The illustration below shows a range of cataract severity.

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Diagram showing the front, interior and back of an eye lens