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How do bifocals and trifocals work?

April 26, 2017bifocals trifocals

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How do bifocals and trifocals work?

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The top portion of a segmented lens is normally used for distance vision, the bottom for near vision. When you look straight ahead, you will be using the distance portion of the lens; when you look down to read, the lens will bring the near vision segment into the line of sight.