Lesson 5: The Eye

Question 1

What type of organ is the eye?

Answer 1

• The eye is a “sense organ”, containing recpetors sensitive to light intensity and colour.

Question 2

What is the function of the “cornea?”

Answer 2

• Transparent layer of the eye.
• The function of the cornea is to start the focussing of the light rays.

Question 3

What is the function of the “lens?”

Answer 3

• Lens focusses light rays onto the back of the eye (retina.)
• Changes shape to focus on either near/ distant objects.

Question 4

What is the function of the “retina?”

Answer 4

• Contains receptor cells for light that allow us to detect light intensity/ light colour.

Question 5

What is the function of the “optic nerve?”

Answer 5

• Carries electrical impulses from the receptors on the retina to the brain.

Question 6

What is the function of the “sclera?”

Answer 6

• White part of the eye.
• Tough outer structure that protects the eye.

Question 7

What is the function of the “ciliary muscles” and “suspensory ligaments?”

Answer 7

• Control the shape of the lens for focussing on either near/ distant objects.

Question 8

What does the pupil do?

UNDERSTANDING!!

Answer 8

• The pupil allows light rays to pass into the eye.

Question 9

What is the function of the iris?

Answer 9

• Iris = coloured part of the eye.
• Function of iris = contains muscles that control the size of the pupil.

Question 10

Describe what happens to the eye in dim light.

Answer 10

• Drop in light intensity is sensed by light receptors in the retina.
• Light receptors send electrical impulses to the brain.
• Brain sends electrical impulses to muscles in the iris.
• The muscles relax - cauing the pupil to become larger.
• So… more light can enter the eye.

Question 11

Why is the change of size of the pupil a reflex action?

Answer 11

• It is a reflex action as it doesn’t include the conscious part of the brain.

Question 12

Describe what happens to the eye in bright light.

Answer 12

• SAME AS DIM!
• But the muscles in the iris contract rather than relax!
• This makes the pupil smaller.
• This reduces the amount of light that can enter the eye.

Question 13

Why is it important for the pupil to change size in bright light?

Answer 13

• To make sure not too much light enters the eye.
• As this could damage the RETINA!

Question 14

What is “accommodation?”

Answer 14

• The ability to change the shape of the lens to focus on near/ distant objects.

Question 15

Why does the lens need to become thinner when we focus on distant objects?

Answer 15

• Thinner: lens only SLIGHTLY REFRACTS light rays.
• Distant objects - light rays only need to be focussed a relatively small amount.

Question 16

Why does the lens need to become thicker when we focus on near objects?

Answer 16

• Thicker: lens refracts light rays more strongly.
• Light from near objects needs to be focussed a large amount.

Question 17

What happens to the ciliary muscle and suspensory ligaments when we focus on near objects?

Answer 17

• Ciliary muscle contracts
• Suspensory ligaments loosen.
• Lens becomes thicker and now refracts light rays more strongly.

Question 18

What happens to the ciliary muscle and suspensory ligaments when we focus on distant objects?

Answer 18

• Ciliary muscle relaxes
• Suspensory ligaments tighten
• Lens is pulled thin and only slightly refracts light rays.

Question 19

What is long- sightedness/ what is another word for it?

Answer 19

• When people can focus on distant objects but not near objects.
• Hyperopia.

Question 20

What are the 2 reasons that light is focussed at a point behind the retina for people who are long- sighted?

Answer 20

• The eyeball is too short.
• Lens is less elastic (like in elderly) so can’t become thick enough to focus on near objects.

Question 21

How can long- sightedness be treated?

Answer 21

• Convex lenses.
• This refracts the light rays so they focus on the retina.

Question 22

What is short sightedness/ what is another word for it?

Answer 22

• People who can focus on near objects but not distant objects.
• Myopia.

Question 23

What are the 2 reasons that light is focussed at a point in front of the retina in short- sighted eyes?

Answer 23

• The eyeball is too long.
• Lens is too thick

Question 24

How can short- sightedness be treated?

Answer 24

• With concave lenses
• Partially unfocusses light rays so that they focus on the retina.

Question 25

What are the 3 different ways long- sightedness/ short- sightedness can be treated other than with glasses?

Answer 25

1.) Hard and soft contact lenses
2.) Laser surgery to change shape of cornea (refract light to a greater/ lesser extent.)
3.) Artificial lens replacement.