Why Do I Need Glasses?
Refraction refers to the way that light rays are focused in your eye. The focusing of light in your eye depends on three elements: the curvature of the cornea, the power of the lens and the length of the eye.
If these elements are not perfectly coordinated, various refractive problems develop. These problems are in no way unusual or strange. They are known as:
Myopia / nearsightedness
Myopia is characterized by an eye that is too long in relation to the rest of its parts or by a cornea with more curvature than normal. As a result, the image falls before the retina and is processed by the brain as a blurred object. People with myopia see near objects more clearly than distant objects because the light rays from near objects are still diverging when they reach the eye and are focused on the retina.
Hyperopia / farsightedness
Hyperopia is characterized by an eye that is too short in relation to the rest of its parts or by a cornea that is flatter than normal. As a result, the light rays do not have enough space to converge on the retina and be focused. People with hyperopia see both distant and near objects blurred because light rays from those objects are focused behind the eye.
Presbyopia means the need for reading glasses, or an "ageing eye". Most people around the age of 40 will find that close objects appear blurry. This occurs because the lens in your eye begins to harden and loses its elasticity. This condition cannot be overcome by having LASIK or INTACS, but rather corrected with bifocals or reading glasses.
Astigmatism is an inability of the cornea to have one focal point because the curvature of the cornea is not symmetrical. In other words, the cornea has two curvatures, making it resemble a football, instead of a basketball.