What are Refractive Errors?
The cornea and lens bend or refract light rays so they can be focused on the retina, the nerve layer that lines the back of the eye. The retina receives the picture formed by these light rays and sends the image to the brain through the optic nerve. A refractive error means that the shape of the eye does not allow the light to be properly refracted making images blurry.
Refractive errors include
- Myopia (nearsightedness).
- Hyperopia (farsightedness).
What is myopia (nearsightedness)?
Myopia (nearsightedness) occurs when light rays are focused in front of the retina instead of directly on the retina. Myopia is a vision problem experienced by approximately one-third of the population. When the eyeball is too long from front to back, the image of a distant object focuses in front of the retina, instead of directly on it. As a result, the distant object appears blurred. The more myopic the eye, the closer an object must be before it is in sharp focus. Nearsighted people have difficulty seeing objects at a distance, such as highway signs, but usually can see up-close for tasks such as reading or sewing.
Some people with myopia can use their natural nearsightedness to read without glasses at an age when other people must wear reading glasses. However, if they have refractive surgery to correct myopia, they may be able to see distant objects without glasses, but will probably need to wear glasses to read sometime after age 40, due to presbyopia.
What is hyperopia (farsightedness)?
Hyperopia or farsightedness occurs when light rays are not bent enough to focus on the retina. Hyperopia is a common vision problem, affecting about one-fourth of the population. If the eye is too short from front to back, light rays reach the retina before they converge (focus). People with hyperopia can sometimes see distant objects very well, but may have difficulty seeing objects that are close.
Young eyes can sometimes compensate for this refractive error —- depending on age and the degree of hyperopia present. But with aging, the human lens loses this ability and a hyperopic person eventually may have difficulty seeing objects at a distance, as well as those that are nearby. In fact by age 40, even those with little or no refractive error will begin to experience difficulty focusing on close objects.
What is astigmatism?
What are the signs of astigmatism?
With increasing age, the lens inside of the eyes loses the ability to focus on nearby objects. The problem usually manifests itself around age 40 and can be corrected with bifocals or reading glasses. This is a normal aging process, called presbyopia and all people develop.
Some people with myopia can use their natural nearsightedness to read without glasses at an age when other people must wear reading glasses. However, if they have refractive surgery to correct myopia, they will be able to see distant objects without glasses, but probably will need to wear glasses to read sometime after age 40 due to presbyopia.