vision

structure and function of the eye

The structure of the human eye is shown in Figure 22.24. Find each structure in the diagram as you read about it below. The cornea is the transparent outer covering of the eye. It protects the eye and also acts as a convex lens, helping to focus light that enters the eye. The pupil is an opening in the front of the eye. It looks black because it doesnt reflect any light. It allows light to enter the eye. The pupil automatically gets bigger or smaller to let more or less light in as needed. The iris is the colored part of the eye. It controls the size of the pupil. The lens is a convex lens that fine-tunes the focus so an image forms on the back of the eye. Tiny muscles control the shape of the lens to focus images of close or distant objects. The retina is a membrane lining the back of the eye. The retina has nerve cells called rods and cones that change images to electrical signals. Rods are good at sensing dim light but cant distinguish different colors of light. Cones can sense colors but not in dim light. There are three different types of cones. Each type senses one of the three primary colors of light. The optic nerve carries electrical signals from the rods and cones to the brain.

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how we see

As just described, the eyes collect and focus visible light. The lens and other structures of the eye work together to focus a real image on the retina. The image is upside-down and reduced in size, as you can see in Figure 22.25. The image reaches the brain as electrical signals that travel through the optic nerve. The brain interprets the 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 is always right-side up. The brain also tells us what we are seeing.

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vision problems

Many people have vision problems. The problems often can be corrected with contact lenses or lenses in eyeglasses. Some vision problems can also be corrected with laser surgery, which reshapes the cornea. Two of the most common vision problems are nearsightedness and farsightedness. You may even have one of these conditions yourself. Both are illustrated in Figure 22.26 and in the video at this URL: (1:08). MEDIA Click image to the left or use the URL below. URL: Nearsightedness, or myopia, is the condition in which nearby objects are seen clearly, but distant objects are blurry. It occurs when the eyeball is longer than normal. This causes images to be focused in front of the retina. Myopia can be corrected with concave lenses. The lenses focus images farther back in the eye, so they are on the retina instead of in front of it. Farsightedness, or hyperopia, is the condition in which distant objects are seen clearly, but nearby objects are blurry. It occurs when the eyeball is shorter than normal. This causes images to be focused in back of the retina. Hyperopia can be corrected with convex lenses. The lenses focus images farther forward in the eye, so they are on the retina instead of behind it.

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instructional diagrams

No diagram descriptions associated with this lesson

questions

Structures of the eye that help to focus light include the

a. iris.

-->  b. cornea.

c. retina.

d. two of the above

Which statement about the lens of the eye is true?

a. It is a concave lens.

-->  b. Its shape is controlled by muscles.

c. It is the only structure in the eye to focus light.

d. all of the above

Which choice shows the correct order in which light passes through structures of the eye?

a. lens, pupil, cornea

b. pupil, cornea, lens

-->  c. cornea, pupil, lens

d. cornea, lens, pupil

Images form inside the eye on the

a. corne

b. iris.

c. pupil.

-->  d. retina.

Why does the pupil of the eye look black?

a. It reflects only black light.

-->  b. It does not reflect any light.

c. It consists of a black membrane.

d. It absorbs all the light that strikes it.

The colored part of the eye is the

a. lens.

b. rod.

-->  c. iris.

d. cone.

The function of the structure in question 3 is to

a. change images to electrical signals.

b. fine-tune the focus of light.

-->  c. control the size of the pupil.

d. adjust the position of the lens.

Functions of the cornea of the eye include

-->  a. protecting the eye from injury.

b. adjusting the position of the lens.

c. controlling how much light enters the eye.

d. two of the above

The image formed on the retina by the lens of the eye is

a. virtual.

b. enlarged.

-->  c. upside-down.

d. two of the above

Electrical signals from the retina reach the brain through the

a. visual nerve.

-->  b. optic nerve.

c. optic rod.

d. electrical ro

Which statement about myopia is true?

a. It is also called farsightedness.

b. It can be corrected with convex lenses.

-->  c. It occurs when the eyeball is longer than normal.

d. It causes both near and distant objects to appear blurry.

What happens when the eyeball is shorter than normal?

a. Images are focused in back of the retin

b. Distant objects are seen clearly.

c. Nearby objects appear blurry.

-->  d. all of the above

One function of the cornea is to protect the eye.

-->  a. true

b. false

The role of the pupil is to help focus light.

a. true

-->  b. false

Images formed by the eye are upright and virtual.

a. true

-->  b. false

We can see only if information from the eyes reaches the brain.

-->  a. true

b. false

Rods can sense dim light but not colors of light.

-->  a. true

b. false

The eyes and brain work together to enable vision.

-->  a. true

b. false

The pupil helps to focus light that enters the eye.

a. true

-->  b. false

The lens changes shape to focus images of close or distant objects.

-->  a. true

b. false

There are two different types of rods in the retina.

a. true

-->  b. false

The brain interprets signals from the retina as shape, color, and brightness.

-->  a. true

b. false

The brain interprets images on the retina as though they were upright.

-->  a. true

b. false

Laser surgery corrects vision problems by changing the shape of the lens.

a. true

-->  b. false

The role of the iris is to control the size of the pupil.

-->  a. true

b. false

The lens normally focuses images on the optic nerve.

a. true

-->  b. false

Hyperopia is also called nearsightedness.

a. true

-->  b. false

nerve cell in the retina that senses dim light

a. eye

-->  b. rod

c. cornea

d. cone

e. iris

f. retina

g. pupil

colored part of the eye

a. eye

b. rod

c. cornea

d. cone

-->  e. iris

f. retina

g. pupil

opening at the front of the eye that lets in light

a. eye

b. rod

c. cornea

d. cone

e. iris

f. retina

-->  g. pupil

nerve cell in the retina that senses colors of light

a. eye

b. rod

c. cornea

-->  d. cone

e. iris

f. retina

g. pupil

organ specialized to collect light and focus images

-->  a. eye

b. rod

c. cornea

d. cone

e. iris

f. retina

g. pupil

transparent outer covering of the eye

a. eye

b. rod

-->  c. cornea

d. cone

e. iris

f. retina

g. pupil

membrane lining the back of the eye

a. eye

b. rod

c. cornea

d. cone

e. iris

-->  f. retina

g. pupil

diagram questions

No diagram questions associated with this lesson