Eyes are organs that detect light, and send electrical impulses along the optic nerve to the visual and other areas of the brain. Light rays are always traveling around you from the sun or various lamps. These light are constantly travel in a straight line. Why your friends have perfect eyes, while you have to wear a pair of eyeglasses all the time?
The bending of a light ray is also called refraction which is due to a change in its speed. The normal eye can refract or focus light without the help of any glasses. If the eye cannot focus an image sharply and requires another lens to assist it, then it is said that you have a refractive error. There are many types of refractive errors, and different conditions can result from them, including myopia, hyperopia, and astigmatism.
The ability for eyes to focus light sharply on the retina is based on several features.The overall length of the eye is an important factor in refraction. If the eyes are too long, images mistakenly focused in front of the retina are out of focus by the time they actually hit the retina. This results in myopia. If the eye is too short, images never have a chance to achieve focus by the time they hit the retina. In this case, the patient would be farsighted. When the cornea is not spherical, then the image is refracted or focused irregularly to cause astigmatism.
A long time ago,eyeglasses has been the most common measures to correct myopia, amblyopia, hyperopia and other vision problems. Lenses have been placed in front of the eye to bend incoming light rays, and to assist the eye to achieve proper focus squarely on the retina. Your prescription is determined by the degree of your refractive error, which is diagnosed by a professional optometrist.
With the advancement of technology, refractive surgery, such as LASIK is becoming popular. Surgeons use special techniques during these procedures to reshape the cornea of the eye, changing the way it bends light. Then the eye becomes able to focus light rays directly on the retina, for clear vision.