Visual defects Flashcards Preview

CM Clinical Symposia > Visual defects > Flashcards

Flashcards in Visual defects Deck (68):
1

Pupil

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

2

Iris

Colour, 2 muscles - may vary in size

3

Cornea

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

4

Extraocular muscles

3 pairs

5

Conjuctiva

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

6

Optic nerve

Carries axons from retina > brain

7

Lens

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

8

Vitreous humour

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

9

Retina

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

10

Fovea

Highest visual acuity, light can reach photoreceptors directly

11

Refraction

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

12

As light passes through the cornea

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

13

Closer images and refraction

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

14

Lens accomodation

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

15

Ciliary muscles

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

16

Emmetropic eye

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

17

Hyperopia

Farsightedness

18

Farsightedness/hyperopia

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

19

Myopia

Nearsightedness

20

Nearsightedness/myopia

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

21

Photorefractive keractectomy

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

22

Macula

Central vision

23

Fovea

Central/thinner region of retina

24

Optic disc

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

25

The retina

- 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

26

Photoreceptors - absorption occurs in

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

27

Photoreceptors transduce

Light energy > changes in membrane potential

28

Cones

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

29

Rods

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

30

Rhodoposin

Pigment in rods (receptor protein - opsin)

31

Scotopic

Night time lighting

32

Mesopic

Twilight

33

Photopic

Daytime lighting

34

Cone

Three types of opsins (blue, green, red)

35

Which colour has highest wavelength?

Red

36

Young-Helmholtz trichromatic theory

When all cone types are equally active perceive white

37

Trichromat

Normal colour vision

38

'Alternate' perception of colour

Anomalous trichromat

39

Dichromat

Colour blindness

40

Why is colourblindness more common in men?

Genes for red and green pigments are carried on X chromosome

41

Bipolar cells

Create direct pathway from photoreceptors to ganglion cells

42

Horizontal/amacrine

Interneurone - indirect pathway modulators

43

Retinal ganglion cells

Axons leave eye > optic nerve

44

Signal transduction in photoreceptors

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

Bipolar cells

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

Receptive field (RF)

Area of retina that alters bipolar Vm in response to light

47

RF 'centre'

Makes direct contact with bipolar

48

RF 'surround'

Makes indirect contact with bipolar via horizontal cells

49

On-centre bipolar cell (centre)

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

On-centre bipolar cell (surround)

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

3 Types of retinal ganglion cells

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

52

Magnocellular

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

53

Parvocellular

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

54

Non-M non-P

Medium cell type, 5%

55

Ganglion cells are mainly responsive to

Differences in illumination

56

On-centre ganglion cell depolarised when

Small spot of light projected into middle of receptive field

57

Off-centre ganglion cell depolarised when

Small dark spot presented to middle of its receptive field

58

Colour-opponent ganglion cells

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

Retinotopic organisation

Info stays next to each other

60

LGN projections

Neurons of LGN project to visual cortex via optic radiation

61

M channel

Analysis of object motion (IVCa)

62

P-IB channel

Analysis of object shape (p cell project to IVCB)

63

Blobs

Analysis of object colour

64

Orientation columns

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

65

Ocular dominance columns

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

66

Parallel pathways

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

67

Striate cortex

First region of visual processing in cortex

68

Extrastriate visual processing

1. Striate cortex towards parietal lobe (visual motion)
2. Striate cortex towards temporal lobe (recognition of objects)