Producing double vision? (7)
I believe the answer is:
bifocal
'double vision?' is the definition.
(I've seen this in another clue)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for bifocal that I've seen before include "Like two-part lenses" , "that's seen through" , "Lens with two prescriptions" , "Allowing for distant and near vision" , "Type of spectacles for long and short sight" .)