WEEK 7 - Topic 17 - Focusing Light on the Retina

Question 1

Which type of photoreceptors in the eye responds to the different wavelengths of the visible spectrum?

Answer 1

Cones

Question 2

There are specific cones that respond to specific wavelengths of visible light. True or false?

Answer 2

True

Question 3

All rods can respond to all wavelengths of visible light. True or false?

Answer 3

True

Question 4

Which type of cones will respond to blue, green and red light?

Answer 4

Blue light - blue cones

Green light - green cones

Red light - red cones

Question 5

What type of lens is our human lens?

Answer 5

Convex

Question 6

What happens when light doesn’t hit the retina?

Answer 6

Image is blurred

Question 7

How many times does the light bend as it enters our eye? List the areas.

Answer 7

3 times

• Entering the cornea
• Entering the lens
• Leaving the lens

Question 8

What does the light move through in the eye when humans see shit?

Answer 8

Cornea
Aqueous humour
Lens
Vitreous humour
Entire neural layer of the retina

Question 9

What are the light bending apparatus of the eyes?

Answer 9

Cornea
Aqueous humour
Lens
Vitreous humour

Question 10

Which part of the eye accounts for the majority of the refractory power?

Answer 10

Cornea

Question 11

Is the refractory power of the cornea constant or not?

Answer 11

Constant

Question 12

Is the refractory power of the lens constant or not?

Answer 12

Not constant

Question 13

Why is the refractory power of the lens not constant?

Answer 13

• The lens is highly elastic

- Its curvature and refractory power can actively change (accommodation) to allow fine focusing

Question 14

Which part of the eye can change shape to focus light?

Answer 14

Lens

Question 15

Human eyes are best adapted for distant or close vision?

Answer 15

Distant vision

Question 16

What is accommodation?

Answer 16

The process of changing the refractive power of the lens of the eye to maintain a clear image (focus)

Question 17

When is the refractory power of the lens at its lowest?

Answer 17

• During distant vision

- When lens is at rest

Question 18

Define the “far point of vision”

Answer 18

The far point of vision is the distance beyond which no change in lens (accommodation) is needed for focusing.

Question 19

What distance if the far point for normal eyes?

Answer 19

6 m or 20 feet

Question 20

At 6 m, does the eye need to accommodate?

Answer 20

No.

Question 21

When viewing objects that are distant, do our eyes need to make large or little adjustments for proper focusing?

Answer 21

Little adjustments

Question 22

What happens during distant vision?

Answer 22

The light rays entering the eye from the distant object is nearly parallel.

Sympathetic input causes the

• Ciliary muscle to relax;
• Ciliary zonule tightens, pulls and stretches the lens into flattened shape
• Lens is as thin as possible, at rest and at its lowest refractory power

Question 23

When does the ciliary muscle relax?

Answer 23

• During distant vision, as sympathetic input increases and parasympathetic input decreases

Question 24

(REVISION) What type of muscle is the ciliary muscle?

Answer 24

Smooth muscle

Question 25

When looking at an object at a distance, what are the light rays like?

Answer 25

Light rays from the distant object are nearly parallel

Question 26

Why does the lens need to be flat when looking at a distant object?

Answer 26

Because the light rays from the distant object are nearly parallel.

Question 27

What distance defines distant vision?

Answer 27

When an object is at or more than 6 m away from the eye.

Question 28

What are the processes that must occur when focusing light from a close object? Just list the titles.

Answer 28

- Accommodation of the lenses - Constriction of the pupils - Convergence of the eyeballs

Question 29

Outline accommodation of the lenses needed for close vision

Answer 29

Accommodation is the process of changing the refractory power of the lens of the eye to maintain a clear image (focus). - During close vision, accommodation increases the refractory power of the lens. 1. The ciliary muscles contract 2. Ciliary zonule relaxes and releases tension 3. Lens relaxes and bulges, becoming more spherical/convex

Question 30

What controls the contraction of ciliary muscles?

Answer 30

Parasympathetic fibres of the oculomotor nerves

Question 31

Outline constriction of the pupils needed for close vision

Answer 31

The pupillary reflex of the sphincter pupillae muscles of the iris constricts the pupil to prevent divergent light rays from entering the eye.

Question 32

What is the pupillary reflex mediated by?

Answer 32

Parasympathetic fibres of the oculomotor nerves

Question 33

Outline the convergence of the eyeballs needed for close vision

Answer 33

The medial rectus muscles converge, or medially rotate, the eyeballs towards the object being viewed.

Question 34

What controls the convergence of the eyeballs?

Answer 34

Somatic motor fibres of the oculomotor nerves

Question 35

When looking at an object up close, what are the light rays like?

Answer 35

The light rays are divergent

Question 36

Outline the steps and processes that occur during close vision

Answer 36

1. There is increased firing of parasympathetic fibres of the oculomotor nerves. 2. Accommodation of the lenses - The ciliary muscles contract - Ciliary zonule relaxes and releases tension - Lens relaxes and bulges, becoming more spherical/convex 3. Constriction of the pupils - The pupillary reflex of the sphincter pupillae muscles of the iris constricts the pupil to prevent divergent light rays from entering the eye. 4. Convergence of the eyeballs - The medial rectus muscles converge, or medially rotate, the eyeballs towards the object being viewed. This is controlled by the somatic motor fibres of the oculomotor nerves. 5. Through all these processes, near objects are brought into focus.