Eye Diagram

Focus Correction of the Eye

Light entering the eye is focused onto the back of the eye by the cornea. The cornea is a clear window, which forms the front surface of the eye, its focusing power is determined by its curvature. In order to form a clear image there needs to be a balance between the curvature of the cornea and the focal length of the eye.

The internal lens of the eye also contributes to focus. It allows us to adjust focus from distance to near, as when reading.

Shortsightedness

Shortsightedness is due to the corneal curvature being too steep for the focal length of the eye. The excimer laser corrects this by flattening the curvature of the cornea.

Longsightedness

Longsightedness is due the corneal curvature being too flat for the focal length of the eye. The excimer laser corrects this by steepening the curvature of the cornea.

Astigmatism

Astigmatism is due to irregularity of the curvature of the cornea, being too flat in one direction and too steep in the other direction. The excimer laser reshapes the cornea to regularize the curvature.

Presbyopia

Presbyopia is an ageing change of the eye whereby the internal lens loses its ability to adjust focus from distance to near. This results in people needing reading glasses after the age of 45 years. Laser does not correct presbyopia and people in this age group will need reading glasses after the surgery.