Common Problems With Vision
Myopia (nearsightedness)
Nearly one third of the population is effected by myopia. Humans that suffer from this condition have a difficult time seeing objects from a distance. Myopia occurs when the eye is slightly longer than normal, or if the refractive properties of the lens and cornea are greater than normal. This causes the light rays that form images to focus in front of the retina. Most cases of myopia are hereditary and are detected during childhood. The problem can be corrected by using eye glasses (see below), contacts or laser surgery. It can also be temporarily corrected by wearing special contacts at night that reshape the cornea. This process is refered to as Cornea Refractive Therapy (CRT).
Hyperopia (farsightedness)
Farsightedness effects nearly one forth of the population. People that suffer from this condition have difficulty seeing objects that are close to them, yet can see objects at a distance clearly. Typically, this occurs when the eye is smaller than normal, or if the refractive properties of the lens and cornea are less than normal. As is the case with myopia, humans that suffer from hyperopia can correct this problem by using eye glasses (see below), contact lenses, or by having laser surgery.
The two pictures shown below provide a visual example of both myopia and hyperopia.
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Myopia |
Hyperopia
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Astigmatism
Astigmatism is one of a group of eye conditions known as refractive errors. Refractive errors cause a disturbance in the way that light rays are focused within the eye. Astigmatism often occurs with nearsightedness and farsightedness, conditions also resulting from refractive errors. Astigmatism is not a disease nor does it mean that a person has "bad eyes." It simply means that a variation or disturbance in the shape of the cornea exists.
Astigmatism usually occurs when the front surface of the eye, the cornea, has an irregular curvature. Normally the cornea is smooth and equally curved in all directions and light entering the cornea is focused equally on all planes, or in all directions. In astigmatism, the front surface of the cornea is curved more in one direction than in the other. This abnormality may result in vision that is much like looking into a distorted, wavy mirror. The distortion results because of an inability of the eye to focus light rays to a point.
If the corneal surface has a high degree of variation in its curvature, light refraction may be impaired to the degree that corrective lenses are needed to help focus light rays better. At any time, only a small proportion of the rays are focused and the remainder are not, so that the image formed is always blurred.Usually, astigmatism causes blurred vision at all distances. Some people with very high degrees of astigmatism may have cornea problems such as keratoconus.
Astigmatism is very common. Some experts believe that almost everyone has a degree of astigmatism, often from birth, which may remain the same throughout life. The exact reason for differences in corneal shape remains unknown, but the tendency to develop astigmatism is inherited. For that reason, some people are more prone to develop astigmatism than others. The treatments for astigmatism is as with myopia or hyperopia; eye glasses, contact lenses, and corrective laser surgery are the main options.
Color Blindness
The human eye is stimulated by visible light when it hits the retina. The peripheral cells on the retina (rods) are cells that make vision at night or under low light conditions possible. Cone cells in the center portion of the retina,the macula, make color and detailed vision possible.
Color blindness is a condition effecting less than ten percent of the population. 95 percent of the effected population are males. Some color blindness effects a persons ability to see red (protanomoly) while others have difficulty seeing green (deuteranomaly). Very few people (less than one percent) are unable to distinguish color to any degree (monochromasy).