The shape of the eye determines how well the eye sees. Light shines through the cornea, the front part of the eye and, ideally, should land on the retina. This gives perfect vision without the need for an eye glass prescription. If the eye or cornea has a different shape, this may cause blurry vision and require glasses or contact lenses for clear vision.
Long Eye
Nearsighted, also called myopic, people can see well close-up, but objects in the distance will appear blurry. Myopia results from a long eye. The light passes through the cornea, but due to the length of the eye, cannot reach the retina. Instead, the light focuses in front of the retina, says the National Eye Institute. The proper eyeglass prescription will adjust the way the light passes through the cornea so that it will reach the retina, resulting in good distance.
Short Eye
People with short eyes have hyperopia, or farsightedness. Farsighted people see well in the distance but cannot see well for close work. Short eyes cause the focal point of the light passing through the cornea to be located at a point behind the retina, says the U.S. National Library of Medicine. The proper prescription eyewear will draw the focal point forward, correcting distance vision.
Oblong Cornea
In a normal-shaped cornea, curved around like a basketball, light passes through the cornea and focuses on the back of the eye. If the cornea has an abnormal shape, oblong like a football, the light will not focus on the retina properly. This is called astigmatism. Vision with astigmatism may appear wavy instead of blurry, says The University of Michigan Kellogg Eye Center. During an eye exam, the doctor will check for astigmatism and include this on the eye glass prescription. With the proper correction, the lenses will direct the light through the cornea to improve vision.
Steep Cornea
Some people have a condition that causes the cornea to thin and bulge out in a cone shape, says the National Eye Institute. This condition, called keratoconus, distorts vision, and will often produce extreme astigmatism or nearsightedness. The changes to the cornea occur gradually, and doctors will prescribe eye glasses to correct the way the light enters the eye. However, over time, the person may need to wear special contact lenses to help with vision and slow the continued outward growth of the cornea. For some people, keratoconus may cause corneal scarring, which will permanently damage vision.
