Bifocal
Bifocal lenses are effectively two lens powers combined together to assist with both near and distance vision. The most common use of bifocals is for reading correction in the lower lens together with a modest distance correction in the upper lens, giving sharp vision at two distinct distances. Bifocals can also be supplied with a clear (upper) lens for those requiring reading glasses but not wanting the inconvenience of removing their spectacles every time they look up.
