Correcting Eyesight Problems and Disorders
The front surface of the eye (cornea) acts as a lens. With perfect sight, the image is brought into sharp focus on the back surface of the eye (retina).

Vision problems occur when the image is not accurately focused on the back of the eye and vision is blurred.

The usual method for correcting eyesight problems and disorders is with glasses or contact lenses. Their power is measured in dioptres, according to the strength of a round (spherical) lens that enables the clearest possible vision.