Figure 17 The eye is the organ that provides you with sight. Light passes through the cornea, pupil, and lens before striking the retina. Signals from light-sensitive nerves on the retina are sent through the optic nerve to the brain. Predicting What may result if the eyeball has an elongated (too long) shape?
dPupil and Iris
After the cornea, light rays pass through the pupil, the part of your eye that looks black. The pupil is the opening that allows light rays to enter your eye. The colored part of your eye, the iris, contracts and expands to control the amount of light that enters your eye. The controlled movement of the iris is regulated by signals from your brain.
Lens
After passing through the pupil, light enters the convex lens in your eye. The lens is a sealed capsule containing a clear fluid. This lens focuses the light onto the light sensor cells at the back of the eye. As you change your focus from near to distant objects, muscles inside the eye change the shape of the flexible lens. The muscles relax and the lens becomes thinner and flatter. If you read for a long time, you'll notice that your eyes become tired and feel strained. This is because the muscles have been contracting for a long time. The best way to relax your eyes is to look far away.
Retina
The focused, refracted light is collected at the retina. The retina is the inner surface of the eye. Its surface is covered by light-sensitive nerve endings called rods and cones. The rods and cones convert the light into electrical signals that are sent to the brain through the optic nerve. The area of the retina where the nerve endings come together to form the optic nerve creates a blind spot. This blind spot has no rods or cones and cannot sense light.
Which part of the eye controls how much light enters?
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