We have generally the
following lenses in an optical shop near our locality. The lenses are usually
prescribed by the Ophthalmologist. There could be more but there are important.
Convex lenses :
People suffering from
farsightedness or hypermetropia cannot see nearby objects clearly -
rather, they cannot focus them clearly on retina. So
these converging lenses are prescribed. Depending on requirement, plano
convex or double convex may be prescribed.
from shortsightedness or myopia focus objects from distance, at a
location in front of retina. So they are prescribed diverging
lenses. Depending on requirement, plano concave or double concave may be
suffering from astigmatism have a trouble that they cannot focus correctly
the objects in all directions. Objects in vertical direction and
horizontal direction are not both focused correctly at the same time.
Depending on requirement plano cylindrical or
total cylindrical lenses may be prescribed.
It is also possible that people are given bifocal lenses with two lenses combined
in one spectacle.
There are more lenses like achromatic cameras to
correct chromatic and spherical aberrations.
Lenses used in digital cameras, cell phones, PC
cameras etc. Perhaps these are available in a different shop or directly from a dealer.