The focus power of the eye is too great so that light focuses in front of the retina. Such eyes are said to be short-sighted because the focus of the eye is set for near. The focus power must be reduced in order to see clearly for distance.

This can be achieved by a minus (negative) power lens. The spectacle prescription for a low degree of myopia might read “–1.50” to indicate that the focus power of the eye needs to be reduced by one and a half diopters.

The focus power of the eye can be reduced by surgery in one of two ways – by making the cornea (the front window of the eye) flatter or by replacing or augmenting the natural lens of the eye with an artificial lens of lesser power.