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Year Invented - 1827
Inventor - John Isaac Hawkins (British inventor and engineer)
Function - The word "trifocal" literally means "three focuses," as the lens powers are split in thirds to help people see clearly at three different distances.
Details - The upper part of the lens corrects distance vision, the middle intermediate vision, and the lower near vision. There are common types: D-shaped (medium lower intermediate/near ovals), executive (33/33/33 lens split), and round-segmented (small intermediate/near circles).
Visual representation of executive-style trifocals
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