Hi Karen -
I used these for the past two weeks while my bifocal
computer/reading glasses were being repaired.
I found them at Longs drug store.
The display has a chart which shows you which strength to buy. They
are little flexible half-circles, and are designed to make
sunglasses into reading glasses.
You clean your glasses, and while the lenses are still wet, you
place the lenses inside the lens of your glasses and work out the
bubbles, which is very easy to do. They are easily repositioned so
that you can place them on your lenses wherever you like, and they
can be trimmed if they are too large. I referred to them as my
do-it-yourself bifocals. Once in place they don't move, but are
easily peeled off when you are done with them.
I dreaded attempting to do any kind of reading or close-up work when
my glasses broke and these were an extremely satisfactory solution