How can optometrists measure bifocal glasses when they only have 1/2 of a lens?

Question

And/Or: Can progressive bifocals be measured and duplicated?

In: 2

Answer 1

The optometrist doesn’t measure your lenses. The optometrist measures your visual acuity at various distances. Bifocal and progressive lenses are made to vary the distance at which the wearer is able to bring objects into focus depending on which part of the lens the wearer looks through.