What is a refractive error?
The most common eye disorders are refractive (visual) errors. Refractive error occurs when the image of an object that you are viewing is not focused properly onto your retina (the light-sensitive tissue in the back of the eye).
For perfectly clear vision, the image of a viewed object needs to be focused onto the retina, just as a camera has to be focused properly in order to take a clear picture.
If the image is not focused exactly on the retina, then the image will be blurred, just like an out-of-focus photograph. In this case, you would have a refractive error.
Refractive errors occur when there is a mismatch between the length of the eye, and its optical power. These mismatches usually originate during childhood, when the eyes are growing. The exact causes of refractive errors are still being studied, but it is known that both hereditary and environmental influences can affect their development. Most people have some refractive error, but in the majority of cases the error is small causing minimal vision problems and will not require treatment. In fact, the average person is slightly longsighted.
Refractive errors can usually be corrected using spectacles or contact lenses. There are also surgical options such as laser surgery.
There are four main types of refractive errors:
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