By Mr Alex J Shortt
The reason why people need to wear glasses or contact lenses is because there is a problem or an imbalance in the focusing power of the eye.
Patients who are short-sighted or myopic have too much focusing power, so they need to wear a negative power lens in front of the eye in order to bring the image of the world into focus on the retina.
Patients who are long-sighted, do not have enough focusing, so in order to bring the world into focus on the retina, they need to wear a plus lens in front of the eye.
Lastly, astigmatism is a condition where the eye rather than being completely circular has an oval shape to it and this requires and oval shaped or what is called a toric lens to be worn in front of the eye to bring the world into focus.