Lecture 19: Vision

Question 1

What are the 4 features of vision?

Answer 1

• colour
• shapes
• depth
• movement

Question 2

What are the features of vision referred to as?

Answer 2

perceptions

Question 3

Where are the perceptions received?

Answer 3

in the brain

Question 4

What form is information sent into the brain?

Answer 4

action potentials

Question 5

What is the stimulus for vision?

Answer 5

light

Question 6

Where is the sensation of vision located?

Answer 6

in the brain

Question 7

Visible light is only a small band of the electromagnetic spectrum. What are the wavelengths of visible light?

Answer 7

400-750 nm

Question 8

What are the two features that embody our visual system?

Answer 8

wavelength and amplitude

Question 9

Has red got a longer or shorter wavelength than violet?

Answer 9

longer

Question 10

What does the eye do?

it detects _______ and processes _______ information to create visual __________ and guides _______

Answer 10

it detects light and processes visual information to create visual perceptions and guides behaviour

Question 11

The eye consists of what two basic components?

Answer 11

• optical component

- neural component

Question 12

What is the function of the optical component of the eye?

Answer 12

to collect and focus light onto the plane of the retina

Question 13

What is the function of the neural component of the eye?

to convert ________ into patterned changes of ___________ _________ that the brain can decode to create __________ ____________

Answer 13

to convert energy into patterned changes of membrane potential that the brain can decode to create visual perceptions

Question 14

What is the white bit of the eye called?

Answer 14

the sclera

Question 15

At the front of the eye, the sclera is modified to form what structure?

Answer 15

the cornea

Question 16

How is the sclera modified to form the cornea?

Answer 16

the sclera is white because the cells are white and fibrous but the cornea is translucent

Question 17

Where is the cornea located?

Answer 17

at the front of the eye, covering the iris

Question 18

Is the cornea vascular?

Answer 18

no, it is avascular

Question 19

What two things side in front of the cornea?

Answer 19

the conjunctiva and tears

Question 20

Why is the cornea avascular?

Answer 20

to allow light through unhinged by pigmented cells

Question 21

Because the cornea is avascular, how does it get nutrients and get rid of CO2?

Answer 21

through diffusion

Question 22

Where are the extraocular muscles and what are they for?

Answer 22

they are off to the side of the eye and they are needed for moving the eye around in the skull - this is necessary for balance

Question 23

Where is the aqueous humor?

Answer 23

behind the cornea and in-front of the lens

Question 24

What is another name for aqueous humor?

Answer 24

the anterior chamber

Question 25

What is the role of the aqueous humor?

Answer 25

it is fluid filled for inflating the eye and maintaining intraocular pressure

Question 26

What is the normal intraocular pressure in the aqueous humor and what is the name of a condition when this pressure increases?

Answer 26

15mmol Hg | glaucoma

Question 27

Describe the lens of the eye

Answer 27

it is a fibrous capsule with crystallised lens cells held in place by zonular fibres

Question 28

Is the lens avascular? Why or why not?

Answer 28

yes it is | this is to help get light in unhinged

Question 29

Where is the virteous humor?

Answer 29

behind the lens

Question 30

What is the virteous humor made of?

Answer 30

protein (collagen)

Question 31

Where is the retina? What is it part of?

Answer 31

at the back of the eye, coming around the sides- it is part of the brain because it is an extension of the thalamus

Question 32

Where are the choroid pigmented epithelium and where are they located?

Answer 32

they are located behind the retina and they are densely pigmented cells with black pigment to absorb light

Question 33

What is the name of a disorder when the choroid pigmented epithelium are not pigmented and what effect does this have?

Answer 33

this is albinism and this means that the light is not absorbed and so instead it reflects all around the back of the eye so there are visual problems

Question 34

Describe the retina ganglion cells

Answer 34

these line the back of the eye and leave the eye at the optic disc and form the optic nerve going to the brain

Question 35

What is the optic disc?

Answer 35

the blind spot of the eye

Question 36

What is the fovea?

Answer 36

this is a depression in the retina responsible for the strongest vision

Question 37

Is the retina vascularised?

Answer 37

yes

Question 38

Define refraction

Answer 38

this is the bending of light as it passes from one substance to another

Question 39

What is refraction related to?

Answer 39

the difference between the refractive indices of the two media, and to the curvature of the refractive surface

Question 40

Which part of the eye is most responsible for the bending of light?

Answer 40

the cornea

Question 41

What is refractive power and how is it measured?

Answer 41

this is the ability of a substance to bend light and it is measured in diopters which is the reciprocal of focal length in metres

Question 42

A lens that converges light to a focal point 1m beyond the lens has a power of how many diopters?

Answer 42

1

Question 43

A 2 diopter lens would convert rays what distance beyond the lens?

Answer 43

0.5m

Question 44

A 10 diopter lens would convert the rays what distance beyond the lens?

Answer 44

0.1m

Question 45

What is the refractive power of the eye?

Answer 45

60 diopters

Question 46

What is the near response?

Answer 46

when you shift your gaze from distant to near objects

Question 47

During the near response, what three processes occur?

Answer 47

1. accomodation 2. constriction of the pupil 3. convergence of the eyes

Question 48

Define accomodation

Answer 48

the contraction/relaxation of ciliary muscles to alter the lens shape and change the refractive power

Question 49

Describe what the ciliary muscles and zonular fibres are doing when looking at distant objects

Answer 49

the ciliary muscles are relaxed due to low parasympathetic activity, so the zonular fibres are taut and the lens is flattened

Question 50

Describe what the ciliary muscles and zonular fibres are doing when shifting from looking far away to looking close up

Answer 50

the parasympathetic activation of ciliary muscles increases so these contract, there is tension removed from the zonular fibres so the lens becomes more spherical due to natural elasticity

Question 51

When gazing at close up objects, how does the refractive power change compared to looking at far away objects?

Answer 51

when changing gaze from looking far away to close up, the refractive power increases from 60 to 75 diopters

Question 52

Describe myopia

Answer 52

This is a dysfunction in accomodation where people are near sighted because their eyeball is too long. This means that people can see closeup but not far away

Question 53

What causes myopia?

Answer 53

the eye is elongated which means that light is focused in front of the retina so far objects are left out of focus

Question 54

How can myopia be corrected?

Answer 54

with a concave lens

Question 55

Describe hypermetropia

Answer 55

This is far-sightedness which means that you can see far away but not up close.

Question 56

What causes hypermetropia?

Answer 56

The eyeball is too short which means that light focuses behind the retina and so close up objects are out of focus

Question 57

How can hypermetropia be corrected?

Answer 57

with convex lenses to bring the focal point forward

Question 58

Another optical defect is astigmatism. What is this?

Answer 58

This is what the curvature of the cornea and/or the lens is spherical which causes there to be a different amount of refraction in different places. This means there is different focal points at the back of the retina.

Question 59

How can astigmatism be corrected?

Answer 59

with a cylindrical lens

Question 60

Another optical defect is presbyopia. What is this?

Answer 60

This is an age-related loss of accomodation caused by the lens losing elasticity so the near point gets further and further away

Question 61

What is perfect vision called?

Answer 61

emmetropia

Question 62

How can presbyopia be corrected?

Answer 62

with convex lenses to restore near vision

Question 63

Define near point

Answer 63

the point closest to you eyes at which you can see clearly

Question 64

What is a cataract?

Answer 64

This is when the lens becomes opaque because the cells in the lens die. This causes light to scatter not converged so there is a poor quality image

Question 65

How can cataracts be fixed?

Answer 65

through surgery to get the lens removed and a plastic one in to replace it however, you will still need glasses and you will have myopia because you cannot accomodate post surgery

Question 66

As well as accomodation, another process that occurs during the near response is constriction of the pupil. What happens when there is constriction of the pupil?

Answer 66

the improved depth of focus and fewer optical aberrations by excluding edges of the lens (ie. the peripheries are reduced)

Question 67

As well as accomodation, another process that occurs during the near response is convergence of the eyes. What happens during convergence of the eyes? Objects remain in _______ on corresponding parts of the _________

Answer 67

objects remain in register on corresponding parts of the retinae