Friday, 6 December 2013

What causes shortsightedness or myopia?

What causes shortsightedness or myopia?
Symptom: A person with shortsightedness cannot see objects which are far away but can see objects which are nearby.
Reason for the defect: The light rays from the object move through the eye and get converged before the retina. As image of the object is not formed on the retina we cannot see the object.
Causes for the defect:  The lens is too convex or too curved is one of the reason for this defect. Another reason for this defect is the eye ball may become lengthened from front  to back.
How to rectify this defect?
A spectacle with concave lens has to be used for rectifying this defect.  Concave lens is a diverging lens which makes the light rays to travel further and make them to meet on the retina. The power of the lens has to be noted with a negative sign. Shortsightedness or myopia is mainly caused in school going  children.