adjusted to three different focal lengths
a lens like a bifocal but with an additional narrow area ground to adjust the intermediate focus for objects at c. 76 cm (c. 30 in)
- Having three focal lengths.
- Having one section that corrects for distant vision, a second section that corrects for medium vision, and a third that corrects for near vision, as an eyeglass lens.
- A lens having three focal lengths.
- trifocals Eyeglasses having trifocal lenses.