The human eye is responsible for vision, though doctors may prescribe eyeglasses or contacts to correct blurry vision. Eye disease may cause serious damage to the eye, including vision loss. However, knowing details about the human eye may help determine the best way to maintain good vision.
Anatomy for Vision
The cornea covers the front of the eye, a clear window for light to enter. Past the cornea, the iris is the colored muscle of the eye that expands and contracts. The movement of the iris changes the size of the opening into the eye, called the pupil, controlling the amount of light entering the eye. Once through the pupil, light passes through the natural lens of the eye, which reflects the light onto the retina. The retina lines the inside of the eye and transmits the information from the light to the optic nerve. The optic nerve consists of a bundle of nerves that convert the light into visual information, which it then passes on to the brain.
Near & Distance Vision
The shape of the eye plays an important role in vision. In a round eye, light enters the eye and focuses directly on the retina. However, if the eye has a long shape, the light will focus on a spot in front of the retina, giving good near vision but poor vision in the distance, according to the National Eye Institute. This is called nearsightedness. People who have a "short" eye will have a focal point behind the eye. This creates good distance vision, but poor vision for reading, a condition called farsightedness. Doctors refer to these types of vision as refractive errors, meaning the light does not "refract" properly. Prescription eyewear will usually focus the light properly and give clear vision.
Astigmatism
The cornea should round out, like the round edge of a ball. Some people have astigmatism, a condition where the cornea has a football-like shape. This changes the way light enters the eye. Astigmatism will cause blurriness and "vision that is much like looking into a distorted, wavy mirror," explains The University of Michigan Kellogg Eye Center. Astigmatism affects many people, and doctors easily correct this with an eyeglass or contact lens prescription.
Presbyopia
As part of aging, the natural lens in the eye slowly "loses its ability to focus," according to the U.S. National Library of Medicine. Doctors refer to this as presbyopia. Around age 45 and older, people begin to hold reading material further away from their eyes. A simple eyeglass prescription or a pair of over-the-counter reading glasses from a drugstore will help resolve the problem.
