Jayde Winsley, of Ardgowan School, asks :-

Why do people become short-sighted?

Roy Holmes, an eye specialist, responded.

Image clarity depends on the capacity of the curved front of the eye (the cornea) and lens of the eye to bring the rays of light to focus on the seeing part at the back of the eye (the retina). Thus, normal sighted people bring the rays to focus on the retina, long-sighted behind the retina and short-sighted people bring the rays of light to focus in front of the retina. This means that they cannot see clearly in the distance but may be able to see quite clearly at close range.

The determination of short or long sight depends on the curvature of the cornea, the curvature of the lens of the eye and the length of the eyeball. Each of these factors is independently inherited. Thus, some people may be born short-sighted. The majority of short-sighted people however, have normal vision until they are adolescents. At this stage in life there is the adolescent growth spurt when arms and legs and feet grow quite quickly. At the same time as these more obvious parts of the body grow, the eyeball may increase in length and a normal sighted person may become short-sighted. This short-sight may be progressive and will continue as long as there is any growth occurring. In girls it usually stabilises at around sixteen or seventeen, but in boys may continue to progress gradually until the late teens or even the early twenties. Thereafter in both, the condition remains stable and unchanged for the rest of their lives.

There is little good evidence that use of the eyes make short-sight worse, or that any modification of the diet will make any material difference. Short-sight may be corrected by glasses or contact lens and more recently by surgical procedures which alter the curvature of the cornea. This latter is currently accomplished by the use of an Excimer Laser which planes off a very fine layer of central cornea altering the curvature of the cornea. This type of treatment is only suitable once the condition becomes stable, that is in people in their very late teens or early twenties and is only appropriate if glasses are unacceptable and contact lens wear proves difficult.