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Unit 19: Biology Part 2 Page 73 of 137
concave lens on glasses or out, like the outside of a bowl, is
contacts. “Concave” means that used in glasses or contacts.
the lens curves inward, like the
inside of a bowl. The concave lens Some people suffer from both
helps focus light on the retina myopia and hyperopia. How can
instead of in front of it, correcting this be? It doesn’t seem possible
the problem. that the eye could be too long and
too short.
Hyperopia, which is also called
farsightedness, affects about one The answer lies in the lens of your
fourth of people, is pretty much the eye. You can think of the lens like
opposite of myopia. In this a trampoline. As you jump up and
disorder, the eye is too short, so down on the trampoline, it moves
images become focused behind the closer or further from the ground.
retina. As a result, people with The lens does a similar thing when
hyperopia can see things clearly you look at things closer together
when they are far away, but not or further away. This makes the
when they are close up. overall shape of the eye change
slightly.
As your trampoline gets older, the
springs may begin to wear down,
and it may become harder for the
trampoline to move. The same
thing happens with the lens in your
eyes.
As a result, many older people
develop hyperopia. If these people
already had myopia, they will need
a lens that has both a concave and
convex part. Bifocals are glasses
Figure 58 – When the eye is too that have these two parts.
short, hyperopia occurs, and
images are focused behind the These glasses were invented by
retina. Benjamin Franklin over 200 years
ago, and are still used today.
To correct hyperopia, a convex
lens, which is a lens that curves
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