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CM Clinical Symposia > Visual defects > Flashcards

Visual defects Flashcards

1
Q

Pupil

A

Opening that allows light to enter the eye, seems dark because of the light absorbing pigment epithelium in retina

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2
Q

Iris

A

Colour, 2 muscles - may vary in size

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3
Q

Cornea

A

Glassy transparent external surface of eye, lacks blood vessels, nourished by aqueous humour, continuous with sclera

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4
Q

Extraocular muscles

A

3 pairs

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5
Q

Conjuctiva

A

Membrane that folds back from inside of eyes and attaches to sclera

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6
Q

Optic nerve

A

Carries axons from retina > brain

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7
Q

Lens

A

Transparent structure suspended by ligaments (zonule fibres), attached to ciliary muscles control shape of lens

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8
Q

Vitreous humour

A

Viscous jellylike substance, between lens and retina, keeps eye spherical

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9
Q

Retina

A

Where light is transformed into neural activity (part of CNS)

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10
Q

Fovea

A

Highest visual acuity, light can reach photoreceptors directly

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11
Q

Refraction

A

Bending of light rays,occurs when light passes from one transparent medium (air) to another (cornea), bends towards a line that is perpendicular to the border betwen media

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12
Q

As light passes through the cornea

A

Light rays that strike curved surface of cornea bend so they converge on back of eye > retina

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13
Q

Closer images and refraction

A

Require greater refractive power to bring them into focus, occurs by lens changing shape (accommodation)

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14
Q

Lens accomodation

A

Rounding of lens increases curvature of lens surface and increases refractive power, ability to accomodate lens changes with age

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15
Q

Ciliary muscles

A

Allow lens to change shape, contraction relieves tension of zonule fibres allowing it to become rounder

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16
Q

Emmetropic eye

A

Normal - focuses parallel light rays on the retina without need for accommodation

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17
Q

Hyperopia

A

Farsightedness

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18
Q

Farsightedness/hyperopia

A

Eye too short, light focuses behind retina, convex lens used for refraction to allow near objects to be brought to focus

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19
Q

Myopia

A

Nearsightedness

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20
Q

Nearsightedness/myopia

A

Eyeball too long, parallel light rays converge before retina, concave lens refraction to allow distant objects to be brought into focus

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21
Q

Photorefractive keractectomy

A

Corrective laser surgery, uses laser to reshape the cornea and increase/decrease amount of refraction possible

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22
Q

Macula

A

Central vision

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23
Q

Fovea

A

Central/thinner region of retina

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24
Q

Optic disc

A

Origin of blood vessels, where optic nerve axons exit, blind spot

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25
Q

The retina

A
  • Light is focused by cornea and lens > vitreous humour > retina
  • Pigment epithelium (behind retina), filed with melanin - absorbs light not absorbed by retina
  • Light passes through all retinal cells > photoreceptors
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26
Q

Photoreceptors - absorption occurs in

A

Outer segments of photoreceptors (stack of membranous disks - light sensitive photopigments)

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27
Q

Photoreceptors transduce

A

Light energy > changes in membrane potential

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28
Q

Cones

A

Lower sensitivity, day light, colour, fast response, high acuity, concentrated in fovea, trichromatic

29
Q

Rods

A

High sensitivity, more photopigment, high amplication, slower response, low acuity, not in fovea, lots of them connected to less neurones than cones

30
Q

Rhodoposin

A

Pigment in rods (receptor protein - opsin)

31
Q

Scotopic

A

Night time lighting

32
Q

Mesopic

A

Twilight

33
Q

Photopic

A

Daytime lighting

34
Q

Cone

A

Three types of opsins (blue, green, red)

35
Q

Which colour has highest wavelength?

A

Red

36
Q

Young-Helmholtz trichromatic theory

A

When all cone types are equally active perceive white

37
Q

Trichromat

A

Normal colour vision

38
Q

‘Alternate’ perception of colour

A

Anomalous trichromat

39
Q

Dichromat

A

Colour blindness

40
Q

Why is colourblindness more common in men?

A

Genes for red and green pigments are carried on X chromosome

41
Q

Bipolar cells

A

Create direct pathway from photoreceptors to ganglion cells

42
Q

Horizontal/amacrine

A

Interneurone - indirect pathway modulators

43
Q

Retinal ganglion cells

A

Axons leave eye > optic nerve

44
Q

Signal transduction in photoreceptors

A

If light of correct wavelength hits photo receptor stop releasing neurotransmitter, stimulus is light of wrong wavelength/no light, GMP not able to open Na+ channels

45
Q

Bipolar cells

A

On - depolarise in response to light
Off - depolarise in response to dark
Direct - input from receptive field centre
Indirect - input from receptive field surround

46
Q

Receptive field (RF)

A

Area of retina that alters bipolar Vm in response to light

47
Q

RF ‘centre’

A

Makes direct contact with bipolar

48
Q

RF ‘surround’

A

Makes indirect contact with bipolar via horizontal cells

49
Q

On-centre bipolar cell (centre)

A
  1. Light in centre
  2. Photoreceptor hyperpolarised
  3. Less glutamate released from photoreceptor
  4. mGluR6 on ON-bipolar surface less active allowing Na channel to open > depolarisation
50
Q

On-centre bipolar cell (surround)

A
  1. Light in surround, dark in centre
  2. Photoreceptor in centre depolarised/surround hyperpolarised
  3. More glutamate released from centre photoreceptor/less from surround > horizontal cells hyperpolarised
  4. mGluR6 on ON-bipolar cell surface more active closing Na channel > hyperpolarisation/reduction in GABA release from horizontal cells > depolarised central photoreceptor (more bipolar cell hyperpolarisation)
51
Q

3 Types of retinal ganglion cells

A
  1. Magnocellular (M-type)
  2. Parvocellular (P-type)
  3. Non-M non-P (K-type)
52
Q

Magnocellular

A

Larger cell, 5%, large receptive field, important for detection of stimulus movement, connected to rod cells

53
Q

Parvocellular

A

Smaller, 90%, sensitive to stimulus from fine detail, linked to cone cells (colour-opponent cells)

54
Q

Non-M non-P

A

Medium cell type, 5%

55
Q

Ganglion cells are mainly responsive to

A

Differences in illumination

56
Q

On-centre ganglion cell depolarised when

A

Small spot of light projected into middle of receptive field

57
Q

Off-centre ganglion cell depolarised when

A

Small dark spot presented to middle of its receptive field

58
Q

Colour-opponent ganglion cells

A

Light of a particular wavelength in the centre of receptive field will be cancelled out by light of another wavelength in surround
(red-green and blue-yellow)

59
Q

Retinotopic organisation

A

Info stays next to each other

60
Q

LGN projections

A

Neurons of LGN project to visual cortex via optic radiation

61
Q

M channel

A

Analysis of object motion (IVCa)

62
Q

P-IB channel

A

Analysis of object shape (p cell project to IVCB)

63
Q

Blobs

A

Analysis of object colour

64
Q

Orientation columns

A

Simple and complex cells in layers 5 and 6 are orientation selective

65
Q

Ocular dominance columns

A

Cells in layer IVC monocular - receive info from left/right eye

66
Q

Parallel pathways

A
  1. Magnocellular (motion)
  2. Blob (colour)
  3. Parvo-interblob (shape)
67
Q

Striate cortex

A

First region of visual processing in cortex

68
Q

Extrastriate visual processing

A
  1. Striate cortex towards parietal lobe (visual motion)

2. Striate cortex towards temporal lobe (recognition of objects)

CM Clinical Symposia (24 decks)

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