Refractive error is the inability of parallel light rays to form a clear image on the retina after passing through the eye’s refractive action when the eye is not using accommodation, but is imaged in front of or behind the retina. It includes hyperopia, myopia and astigmatism. When the eye is at rest, parallel light is focused on a point in front of the retina after refraction for myopia, a point after the retina for hyperopia, and astigmatism when it cannot be focused into a point. As shown in the figure.