What are refractive errors?

A short-sighted eye has too much focusing power. Images are focused in front of the retina – the area at the back of the eye that interprets images – rather than directly on its surface, resulting in blurred distance but clear near vision.

A long-sighted eye has too little focusing power. Images focus behind the retina, blurring near vision and in severe cases may affect distance vision as well. Hyperopia is not age-related, unlike presbyopia.

Astigmatism is an irregularity in the shape of the cornea. Instead of being round, like a football, it is oval like a rugby ball or egg. Images focused on the retina are distorted, blurring vision at all distances. Astigmatism usually occurs with either myopia or hyperopia.

This is the dependence on reading glasses that comes to most people with age. The lens inside the eye becomes less flexible with time and so cannot focus on close objects. Presbyopia may occur on its own or with any of the other refractive errors.

These are tiny focusing imperfections which decrease the quality of vision. They are as unique to every eye as a fingerprint. Whilst wavefront abnormalities are often not corrected by glasses or contact lenses, they may be successfully treated by laser.