5.59. Vision and the Eye http://www.ck12.org
FIGURE 5.139
- The optic nerve carries electrical signals from the rods and cones to the brain.
Q:The lens of the eye is a convex lens. How would vision be affected if the lens of the eye was concave instead of
convex?
A:A concave lens causes rays of light to diverge, or spread apart. It forms a virtual image on the same side of the
lens at the object being viewed. Therefore, a concave lens would focus the image in front of the eye, not on the
retina inside the eye. No signals would be sent to the brain so vision would not be possible.
How We See
The ability to see is calledvision. This ability depends on more than healthy eyes. It also depends on certain parts
of the brain, because the brain and eyes work together to allow us to see. The eyes collect and focus visible light.
The lens and other structures of the eye work together to focus an image on the retina. The image is upside-down
and reduced in size, as you can see in theFigure5.140. Cells in the retina change the image to electrical signals that
travel to the brain through the optic nerve. The brain interprets the electrical signals as shape, color, and brightness.
It also interprets the image as though it were right-side up. The brain does this automatically, so what we see always
appears right-side up. The brain also interprets what we are seeing.
Q:The part of the brain that processes information from the eyes is the visual cortex. It is located at the back of the
brain. How might an injury to the visual cortex affect vision?
A:An injury to the visual cortex might cause abnormal vision or even blindness regardless of how well the eyes can
gather and focus light.