The normal-sighted eye
Normally, distant and near images can be pictured clearly without any aid on the retina. For near objects the eye has to change the focal length of its lens. This is called accommodation. The lens curves more so that incident light is refracted more. For distant objects the lens flattens. In any case light rays are focused precisely on the retina.
A clear image on the retina is the prerequisite for good vision. Certain conditions must be met in order to produce a correct image in the light-sensitive layer of the eye. The length of the eye for example must be in proportion to its refraction power to see clearly and this is the case with a normal-sighted eye.
If there are any problems our vision is affected and must be corrected.
