For the shortsightedness/nearsightedness, the corrector lenses are concave, that means that they are thiker on the edge then in the center. So they are really unaesthetic and heavy, that's why the strong shortsightedness/nearsightedness have as a choice the traditionnal "magnifiers".

The creation of new materials for the lenses allows today to decrease the tendancy. The shotsightedness/nearsightedness is coming very early for the children (after 8 years old), becoming more pronounced until it becomes stable arround the age of 25 maxi (the average is 20 year old).

Mineral lenses:
The addest, they are able to resist to scratches and can become darker with the brightness. On the other hand, thay are breakable and quite heavy.

Organics lenses:
These "plastic" lenses are used a lot, decause of their lightness and their shock resistance. On the other hand they are subject to scratches.

Composites lenses:
This is the new generation of lenses, which consists in an alloy of composite material and mineral lense. Associated, they've got both possibilities of mineral and composite lenses: lightness and rigidity.
For the moment, their range of application is restricted by the low visual defaults.