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Diagram of the eye
You may wear glasses or contact lenses, but do you really know what's going on inside of your eye?
Glasses are needed when light is focused differently on the retina as it passes through the lens. When the light is being focused directly on the retina, vision is considered normal; however, sometimes it can be processed in front of the retina (nearsightedness) or behind the retina (farsightedness).
Normal
Myopia
Hyperopia
The cornea of a normal eye is generally curved like a basketball. The cornea of an eye with an astigmatism is generally curved like a football. This can cause images to appear blurry and stretched out due to the fact that light rays are prevented from meeting at a common focus.
Astigmatism
Cornea - Vision begins when rays of light are reflected off an object and into the eye through the cornea. The cornea is a transparent outer covering of the eye.
Pupil - The cornea bends and refracts light as it passes through a round hole called the pupil.
Iris - The colored portion of the eye, called the iris, surrounds the pupil and opens and closes the hole to regulate the amount of light going into and out of the eye.
Lens - Once passing through the cornea, the light rays pass through the lens which will slightly change shape to further bend the rays and focus them on the retina at the back of the eye.
Macula - Cones are often concentrated in the macula which is in the center of the retina. Cones provide clear, sharp central vision and detect colors and fine detail.
Retina - The retina is a thin layer of tissue that is located at the back of the eye that contains millions of light sensing nerve cells called rods and cones (these are named for their distinct shapes).
Rods - Rods are located outside of the macula and extend all the way to the outer edges of the retina. They are responsible for side vision (peripheral vision). They help the eyes detect motion and see in dim light as well as at night.
Optic Nerve Leaving the Eye - The cells in the retina covert light into electrical impulses. These impulses are then sent through the optic nerve to the brain where the image can be produced.
(This page was adapted from the American Optometry Association as well as the National Eye Institute)