4.5.2.3 The Eye

Question 1

What is the eye?

Answer 1

• sense organ containing receptors sensitive to light intensity and colour

Question 2

What are the different structures of an eye?

Answer 2

• suspensory ligament
• cornea
• iris
• pupil
• ciliary muscle
• lens
• sclera
• retina
• fovea
• optic nerve

Question 3

What is the function of a cornea?

Answer 3

• refracts light (bends it as it enters eye)

Question 4

What is the function of an iris?

Answer 4

• contains muscles which control how much light enters pupil

Question 5

What is the function of a lens?

Answer 5

• further refracts light to focus it onto retina

Question 6

What is the function of a retina?

Answer 6

• contains the light receptors

Question 7

What is the function of an optic nerve?

Answer 7

• carries impulses between eye and brain

Question 8

What is the function of a sclera?

Answer 8

• tough white outer layer to protect from injury

Question 9

What is the function of ciliary muscles and suspensory ligaments?

Answer 9

• control shape of lens

Question 10

What are the main types of light receptors?

Answer 10

• rods
• cones

Question 11

What are rods?

Answer 11

• more sensitive to light
• useful for seeing in dim light

Question 12

What are cones?

Answer 12

• three different types
• produce colour vision (during day)

Question 13

What is a pupil reflex?

Answer 13

• reflex action that controls amount of light entering eye

Question 14

What happens to the pupil in response to bright light?

Answer 14

• radial muscle relaxes
• circular muscle contracts
• pupil constricts so less light enters

Question 15

What happens to the pupil in response to dim light?

Answer 15

• radial muscle contracts
• circular muscle relaxes
• pupil dilates so more light enters

Question 16

What is accomodation?

Answer 16

• process of changing shape of lens to focus on near or distant objects

Question 17

What happens to the lens when focusing on something near?

Answer 17

• becomes thicker
• allows light rays to refract more strongly
• low muscle tension
• loose suspensory ligament
• contracted ciliary muscle

Question 18

What happens to the lens when focusing on something distant?

Answer 18

• lens is pulled thin
• allows light rays to refract slightly
• high muscle tension
• tight suspensory ligament
• relaxed ciliary muscle

Question 19

What are the common defects of the eyes?

Answer 19

• myopia (short sightedness)
• hyperopia (long sightedness)

Question 20

What can someone see if they are short sighted?

Answer 20

• can see near objects
• can’t focus properly on distant objects

Question 21

How is short sightedness caused?

Answer 21

• eyeball being elongated (distance between lens and retina is too great)
• lens being too think and curved (light focused in front of retina)

Question 22

How can short sightedness be cured?

Answer 22

• concave lenses

Question 23

What can someone see if they are long sighted?

Answer 23

• can see distant objects
• can’t focus properly on near objects

Question 24

How is long sightedness caused?

Answer 24

• eyeball being too short (distance between lens and retina too small)
• loss of elasticity in lens (cannot become thick enough to focus)

Question 25

How is long sightedness cured?

Answer 25

• convex lenses

Question 26

How are the defects treated?

Answer 26

• spectacle lenses
• contact lenses
• laser eye surgery
• replacement lens

Question 27

How do contact lenses work?

Answer 27

• in contact with eye
• float on surface of cornea
• focus and retract light

Question 28

How does laser eye surgery work?

Answer 28

• reshapes cornea surgically
• common for myopia

Question 29

How do replacement lenses work?

Answer 29

• implanting artificial lenses
• placed in front of original lens through a small cut in the cornea