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231 > Lecture 19: Vision > Flashcards

Lecture 19: Vision Flashcards

1
Q

What are the 4 features of vision?

A
  • colour
  • shapes
  • depth
  • movement
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2
Q

What are the features of vision referred to as?

A

perceptions

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3
Q

Where are the perceptions received?

A

in the brain

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4
Q

What form is information sent into the brain?

A

action potentials

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5
Q

What is the stimulus for vision?

A

light

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6
Q

Where is the sensation of vision located?

A

in the brain

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7
Q

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

A

400-750 nm

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8
Q

What are the two features that embody our visual system?

A

wavelength and amplitude

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9
Q

Has red got a longer or shorter wavelength than violet?

A

longer

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10
Q

What does the eye do?

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

A

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

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11
Q

The eye consists of what two basic components?

A
  • optical component

- neural component

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12
Q

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

A

to collect and focus light onto the plane of the retina

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13
Q

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

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

A

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

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14
Q

What is the white bit of the eye called?

A

the sclera

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15
Q

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

A

the cornea

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16
Q

How is the sclera modified to form the cornea?

A

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

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17
Q

Where is the cornea located?

A

at the front of the eye, covering the iris

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18
Q

Is the cornea vascular?

A

no, it is avascular

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19
Q

What two things side in front of the cornea?

A

the conjunctiva and tears

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20
Q

Why is the cornea avascular?

A

to allow light through unhinged by pigmented cells

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21
Q

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

A

through diffusion

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22
Q

Where are the extraocular muscles and what are they for?

A

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

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23
Q

Where is the aqueous humor?

A

behind the cornea and in-front of the lens

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24
Q

What is another name for aqueous humor?

A

the anterior chamber

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25
Q

What is the role of the aqueous humor?

A

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

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26
Q

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

A

15mmol Hg

glaucoma

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27
Q

Describe the lens of the eye

A

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

28
Q

Is the lens avascular? Why or why not?

A

yes it is

this is to help get light in unhinged

29
Q

Where is the virteous humor?

A

behind the lens

30
Q

What is the virteous humor made of?

A

protein (collagen)

31
Q

Where is the retina? What is it part of?

A

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

32
Q

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

A

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

33
Q

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

A

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

34
Q

Describe the retina ganglion cells

A

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

35
Q

What is the optic disc?

A

the blind spot of the eye

36
Q

What is the fovea?

A

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

37
Q

Is the retina vascularised?

A

yes

38
Q

Define refraction

A

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

39
Q

What is refraction related to?

A

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

40
Q

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

A

the cornea

41
Q

What is refractive power and how is it measured?

A

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

42
Q

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

A

1

43
Q

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

A

0.5m

44
Q

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

A

0.1m

45
Q

What is the refractive power of the eye?

A

60 diopters

46
Q

What is the near response?

A

when you shift your gaze from distant to near objects

47
Q

During the near response, what three processes occur?

A
  1. accomodation
  2. constriction of the pupil
  3. convergence of the eyes
48
Q

Define accomodation

A

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

49
Q

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

A

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

50
Q

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

A

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

51
Q

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

A

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

52
Q

Describe myopia

A

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

53
Q

What causes myopia?

A

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

54
Q

How can myopia be corrected?

A

with a concave lens

55
Q

Describe hypermetropia

A

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

56
Q

What causes hypermetropia?

A

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

57
Q

How can hypermetropia be corrected?

A

with convex lenses to bring the focal point forward

58
Q

Another optical defect is astigmatism. What is this?

A

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.

59
Q

How can astigmatism be corrected?

A

with a cylindrical lens

60
Q

Another optical defect is presbyopia. What is this?

A

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

61
Q

What is perfect vision called?

A

emmetropia

62
Q

How can presbyopia be corrected?

A

with convex lenses to restore near vision

63
Q

Define near point

A

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

64
Q

What is a cataract?

A

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

65
Q

How can cataracts be fixed?

A

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

66
Q

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?

A

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

67
Q

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 _________

A

objects remain in register on corresponding parts of the retinae

231 (41 decks)

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