If your vision is blurred, it could simply be due to a refractive error. This means that the light rays do not properly focus on the retina.
Myopia means that the eye is longer or more powerful than normal and the rays of light come to focus in front of the retina, causing the vision to be blurred. Myopia may have its onset in childhood and may progress as a child grows.
Hypermetropia or hyperopia means that the eye is shorter or less powerful than normal and the rays of light come to focus behind the eye.
Astigmatism is caused by the front surface of the eye being shaped more like a rugby ball rather than a soccer ball, causing the rays of light to focus at different points. This results in a blurred image.