Most young people who wear glasses are myopic, that is, they have nearsighted vision. You can tell this if you look through the lens of their glasses. If objects are smaller beyond them, then the person has myopia. If, on the other hand, the lens makes the eyes look larger, then that person is hyperopic, or farsighted.
What is Myopia, and how can it be corrected?
The word “myopia” comes from two roots meaning ‘to shut the eye.’ Perhaps this is because a nearsighted person can at times see blurred objects clearer by squinting. A nearsighted person can see close objects clearly but distant objects will be out of focus. The problem is exacerbated at night.
Technically in a myopic eye light is focusing in the eyeball in front of the retina and, thus, the eye is not receiving a clear image to send to the brain. Two factors cause this problem. First, the shape of the cornea will bend or refract the light abnormally. Second, the eyeball can be too long for light to focus properly. It is not possible to change the shape of the eyeball itself.
Traditionally the problem of myopia is treated with concave lenses. A concave lens is thinner in the middle than on the edge. This causes light to bend in before it enters the eye. The greater the curve of the lens is, the greater the refraction that results. The ability of a lens to refract is also dependent on the density of the material used. Until recent years, glass was the only substance that could be used. When plastic was developed, it was used for glasses, but the lens had to be thicker to refract the same amount as glass. Today dense plastics can refract very adequately and these glasses are much lighter weight than those with glass lenses.
If the light is refracted the correct amount, it will then focus on the retina and the person will have normal vision both for distance and close objects. For some people, the myopia correction is so great that the person’s eyes appear very small when others look at them through their lenses.
Another Nearsighted Vision Solution
Myopia is also corrected by contact lenses. These are small plastic disks that stay on the front of the eye by fluid adhesion. Contact lenses are also designed to refract the light going into the eyeball.
In recent years, thanks to the invention and application of laser light, the problems caused by myopia have be reduced or eliminated for many myopic people. This is called Lasik surgery. LASIK stands for Laser-Assisted in SItu Keratomileusis. In this surgery, an instrument called a microkeratome is used to create a thin, circular flap in the cornea. The surgeon then folds the hinged flap back out of the way to remove some corneal tissue. The goal for a myopic eye is to flatten the cornea so that light focuses on the retina correctly. If it is successful, the patient could be glasses-free for the rest of his or her life.