SHORT SIGHT (MYOPIA)
.A short sighted (myopic) person can usually see objects quite well that are close. i.e. to read and see television, but has difficulty in focussing on objects as they get further away. The further away the object, the more difficult it is to focus correctly.
This condition can be corrected by the use of a MINUS POWERED LENS. (AN EASY WAY TO ASSOCIATE THIS IS MYOPIA = MINUS). The form that a minus powered lens takes is that the centre of the lens is thinner than the edge of the lens, as shown in the diagram below.
The more powerful the lens is the thicker the edge will be in relation to the centre thickness.
(Not to scale)
There are several ways to recognise these lenses, The obvious one is by examining the lens to feel if the lens is thinner in the centre than at the edge, however in some lower-powered lenses this can sometimes be difficult to determine, A simple test is to look through the lens at some printing and if the print seems smaller when viewed through the lens then you have a minus lens, If you are trying to identify which type of lens a person is wearing, the image of the eye is smaller when viewed through the front of the spectacles when they are wearing minus lenses.