1) American invention 2) Corrective lense 3) Dual-focus spectacles 4) Reasons for seeing double 5) Type of glasses 1) Glasses 2) Spectacles 
Bifocals, eyeglasses with two distinct optical powers, are most commonly prescribed to people with presbyopia who also require a correction for myopia, hyperopia, and/or astigmatism. ==History== Benjamin Franklin is generally credited with the invention of bifocals. Historians have produced some evidence to suggest that others may have preceded hi...
Eyeglasses that incorporate two different powers in each lens, usually for near and distance corrections
bifocals Eye glasses with lenses that are divided into two parts. The upper half is for looking at things far away and the lower half is for reading or for looking at things that are near.
noun eyeglasses having two focal lengths