Concept explainers
Why older persons need bifocals and not younger people.
Answer to Problem 4Q
Solution:
As people get older, their near point increases and becomes greater than the ideal value of 25 cm.
Explanation of Solution
As people get older, their eyes can no longer accommodate as well. The flexibility of the eye lens is reduced with age and as a result, it becomes harder for the muscles to change the shape of the lens. In general, people first lose the ability to see far objects, so they need corrective diverging lenses to move their “far point” back toward infinity. Then, as people get older, their near point increases and becomes greater than the ideal value of 25 cm. They may still need the diverging portion of their corrective lenses (kept as the upper part of the corrective lens)so they can have a far point at infinity, but now they also need a converging lens to move the near point back toward 25 cm for seeing close objects.
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