If you can see objects nearby with no problem, but reading road signs or making out the writing on the board at school is more difficult, you may be near- or shortsighted.
This condition is known as myopia, a term that comes from a Greek word meaning “closed eyes.” Myopia is not a disease, nor does it mean that you have “bad eyes.” It simply refers to a variation in the shape of your eyeball. The degree of variation determines whether or not you will need corrective eyewear.
What causes nearsightedness?
Myopia most often occurs because the eyeball is too long, rather than the normal, more rounded shape. Another less frequent cause of myopia is that the cornea, the eye’s clear outer window, is too curved. There is some evidence that nearsightedness may also be caused by too much close vision work.
How does myopia affect sight?
Our ability to “see” starts when light enters the eye through the cornea. The shape of the cornea, lens and eyeball help bend (refract) light rays in such a manner that light is focused into a point precisely on the retina.
In contrast, if you are nearsighted, the light rays from a distant point are focused at a place in front of the retina. As the light will only be focused in that one place, by the time it reaches the retina it will have “defocused” again, forming a blurred image.
Myopia usually occurs between the ages of 8 to 12 years. Since the eyes continue to grow during childhood, nearsightedness almost always occurs before the age of 20. Often the degree of myopia increases as the body grows rapidly, then levels off in adulthood. During the years of rapid growth, frequent changes in prescription eyewear may be needed to maintain clear vision. It is important to bear in mind that the frequent changes in prescription are not making the eyes “weaker”. During the growth period that occurs during the teen years the eye is also growing rapidly and hence the degree of blur is also increasing. As the growth cycle slows the prescription changes slow correspondingly.
How is myopia diagnosed and treated?
Myopia is often suspected when a teacher notices a child squinting to see a blackboard or a child performs poorly during a routine eye screening. Further examination will reveal the degree of the problem.
A comprehensive eye examination will detect myopia. Periodic examinations should follow after myopia has been discovered to determine whether the condition is changing, and whether a change in prescriptive eyewear is needed. Some therapies that have been researched to show reduction in the progression of nearshightedness include ortho keratology and multifocal contact lenses. Eye exams also help to ensure that vision impairments do not interfere with daily activities.
Corrective concave (minus) lenses are prescribed to help focus light more precisely on the retina, where a clear image will be formed.
Depending on the degree of myopia, glasses or contact lenses may be needed all of the time for clear vision. If the degree of impairment is slight, corrective lenses may be needed only for activities that require distance vision, such as driving, watching TV or in sports requiring fine vision.