Having three foci. See t. lens.
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tri·fo·cal (')trī-'fō-kəl adj
1) having three focal lengths
2) of an eyeglass lens having one part that corrects for near vision, one for intermediate vision (as at arm's length), and one for distant vision
trifocal n
1) a trifocal glass or lens
2) trifocals pl eyeglasses with trifocal lenses
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tri·fo·cal (tri-foґ-) (triґfo-kəl) 1. having three foci. 2. containing one part for near vision, one for intermediate, and a third for distant vision; see under lens.Medical dictionary. 2011.