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