Your retina is in the very back of the eye, past the vitreous body. Though it's smaller than a dime, it holds millions of cells that are sensitive to light. The retina takes the light the eye receives and changes it into nerve signals so the brain can understand what the eye is seeing.
The lens is suspended in the eye by a bunch of fibers. These fibers are attached to a muscle called the ciliary (say: sih-lee-air-ee) muscle. The ciliary muscle has the amazing job of changing the shape of the lens. That's right - the lens actually changes shape right inside your eye!
The biggest part of the eye sits behind the lens and is called the vitreous (say: vih-tree-us) body. The vitreous body forms two thirds of the eye's volume and gives the eye its shape. It's filled with a clear, jelly-like material called the vitreous humor. Ever touch toy eyeballs in a store? Sometimes they're kind of squishy - that's because they're made to feel like they're filled with vitreous humor. In a real eye, after light passes through the lens, it shines straight through the vitreous humor to the back of the eye.
The retina uses special cells called rods and cones to process light. Just how many rods and cones does your retina have? How about 120 million rods and 7 million cones - in each eye!
Rods and cones are most sensitive to yellow-green light.
Rods see in black, white, and shades of gray and tell us the form or shape that something has. Rods can't tell the difference between colors, but they are super-sensitive, allowing us to see when it's very dark.
Cones sense color and they need more light than rods to work well. Cones are most helpful in normal or bright light.
The retina has three types of cones - red, green, and blue - to help you see different ranges of color. Together, these cones can sense combinations of light waves that enable our eyes to see millions of colors.
I can’t see…
Sometimes someone's eyeball changes shape and the cornea, lens, and retina no longer work perfectly as a team. The person's eye may focus on what it sees in front of or behind the retina, instead of on the retina. When this happens, some of what the person sees will be out of focus.