Myopia or shortsightedness is relatively easy to understand.
The myopic individual is the one who takes of his glasses to read but needs them to drive a car or watch television
CAUSE OF MYOPIA
In a normal individual, an image of an object that is being looked at is focused onto the retina at the back of the eye.
However in myopia the image is focused not on the retina but in front of it.
As the object that is being looked at moves closer to the eye, the image that is being focused in front
of the retina as above, moves closer to the retina until eventually there is a point at a certain distance away at which the image falls onto the retina again.
The distance to that object varies depending on how short sighted you are. As a rule, the more short sighted you are, the closer you need to hold something to your face to see it.
Clearly being short sighted has its benefits particularly if you are over the age of 45 as it lets you read without glasses. The down side of course is that you can’t see in the distance
MYOPIA AFTER VISION CORRECTION
If you are short sighted and over 45, after vision correction you will no longer be short sighted so your distance glasses are no longer required. HOWEVER since you will still be presbyopic you will no longer be able to see to read. You therefor will be swapping your distance glasses for reading glasses unless you plan in advance to deal with this problem.