Video Transcript
Which of the following types of
lenses can correct nearsightedness? (A) Concave, (B) convex.
Let’s first remember what it means
for an eye to be nearsighted. When an eye is healthy, it takes on
roughly the shape of a sphere. It’s possible though for an eye to
be misshapen or deformed. This changes the way the eye
focuses incoming rays of light. When a nearsighted eye, like this,
looks at an object that’s very near the eye, the eye is able to bend those incoming
rays of light so that they meet at the back of the eye, called the retina. When this happens, the up close
object, whatever it is, is clearly seen.
The problem with a nearsighted eye
shows up when it looks at objects far away. A nearsighted eye bends these
incoming rays so that they cross before they get to the back of the eye. Because the rays are not focused at
the back of the eye, the faraway object looks blurry.
The vision of a nearsighted eye can
be corrected using a lens. The two main types of lens are
convex and concave. A convex lens brings parallel
incoming rays to a focus, while a concave lens spreads out incoming parallel
rays. So let’s think. With our nearsighted eye, light
from objects far away is focused so that the rays meet before they reach the back of
the eye. We could say, in other words, that
this eye focuses light from faraway objects too much.
To move this focus point to the
back of the eye, we could put a concave lens in front of it. This way, light coming in from a
faraway object is spread out so that when the nearsighted eye focuses these rays,
they do meet at the back of the eye, at the retina. Putting this concave lens in place
in front of the nearsighted eye means the eye can even see faraway objects
clearly. For our answer, we choose option
(A). A concave lens can correct
nearsighted vision.
