Nearsightedness is a condition of the eyes in which objects that are close can be seen clearly, but objects that are distant appear blurry or out of focus. The degree of nearsightedness can vary. For some people, objects need to be a few inches away from the eyes in order to be seen clearly. For other people, objects within a few yards of the eyes can be seen clearly. Nearsightedness is also called myopia, and it can develop gradually or it can develop rapidly. Typically it develops and worsens during childhood and the adolescent years and then stabilizes as people reach adulthood.
Improper Refraction
The eye consists of two parts that help to focus incoming rays of light into an image. One part is the cornea, which is the clear part that is on the front of the eye. The lens is the clear part of the eye behind the pupil. The lens changes shape to help focus images on the retina. The cornea and lens should have smooth, curved surfaces that focus the incoming light onto the retina by refracting, or bending, the light, but when either part isn't smooth or does not have the correct curvature, the image isn't focused on the retina. This results in blurred images when objects are not close to the eyes, or nearsightedness.
Heredity
Heredity is believed to be one of the main factors responsible for nearsightedness, according to the American Optometric Association. Parents who have nearsightedness either genetically pass nearsightedness to their children, or they pass along the physical factors that make nearsightedness more likely. Either way, having parents who are nearsighted increases the likelihood of having nearsightedness.
Visual Stress
Even if heredity determines the level of susceptibility to nearsightedness, the way eyes are used could be the actual mechanism by which nearsightedness develops. According to the American Optometric Association, nearsightedness could be brought about by spending a lot of time reading, by working at a computer, which can strain the eyes, and performing other functions that use the eyes for close-up work.
Other Factors
Low light levels can cause nearsightedness, a condition called night myopia. Temporary blurred vision, a type of false myopia, can occur when the eyes are stressed by performing work close to the eyes for extended periods of time, although this condition is generally temporary. People with diabetes can develop symptoms that resemble nearsightedness and result from variations in blood sugar levels. Nearsightedness can also be an early sign of a developing cataract.
