Physiology of Vision Flashcards
1
Q
What is the white of the eye called?
A
The sclerea
2
Q
What is the conjunctiva?
A
The mucous membranes that covers the inside of the papilla fissures the pupil and the white of the sclera
3
Q
What does the conductive not cover?
A
The cornea
4
Q
Which muscle helps with eye movement?
A
The extra ocular muscles
5
Q
What controls the lens?
A
The Zonule fibres
and ciliary mucles
6
Q
What does the lens control?
A
Its Crystalline structure aids focusing of light onto the retina
7
Q
What is the aim of all the structures in the eyes?
A
To provide a clear path for light to reach the retina
8
Q
Describe the cornea
A
It is a Dome-shaped window
It is clear and avascular and continuous with the sclera.
9
Q
What is the role of the cornea?
A
It provides the majority of the focusing power of the eye.
10
Q
Describe the iris
A
Thin, elastic, circular structure
11
Q
What is the role of the iris?
A
It is responsible for controlling the diameter and size of the pupil and thus the amount of light reaching the retina
12
Q
What does the iris determine?
A
The iris determines eye colour.
13
Q
Describe the lens
A
It is a Crystalline structure
14
Q
What can clouding of the lens cause?
A
cataracts
15
Q
What is the aqueous humour?
A
Transparent gel like fluid which fills the anterior part of the eye between the lens and the cornea.
16
Q
What is the aqueous humour formed by?
A
It is formed by the ciliary body and drains via the trabecular meshwork.
17
Q
What does the aqueous humour do?
A
. It maintains intraocular pressure (IOP), nourishes and removes debris from the avascular anterior segments of the eye.
18
Q
What is glaucoma caused by?
A
Glaucoma is caused by an increase in intraocular pressure
19
Q
What is a increase in intraocular pressure caused by and what can it lead to?
A
It is commonly caused by degeneration of the trabecular meshwork reducing drainage of the aqueous humour.
It can cause glaucomas
20
Q
Describe the sclera
A
It is the Fibrous white opaque connective tissue layer covering 5/6 of the eye ball.
21
Q
What is the sclera continuous with?
A
Continuous with the transparent cornea
22
Q
What is the sclera made up of?
A
Type 1 collagen
23
Q
What is the cornea made up of?
A
Type 1 collagen
24
Q
What is the sclera important for?
A
Giving the eye some structure and support
25
Name the 4 layers that are up the posterior eye from outermost
1. Sclera
2. Choroid
3. Retina
4. Vitreous humor/body
26
Describe the choroid
It is a vascular connective tissue layer.
| It contains melanin pigment
27
What does the choroid do?
It nourishes outer 1/3 of the retina
| It also stops a lot of the scattered light from causing damage
28
What is the choroid continuous with?
Continuous with the ciliary body.
29
Describe the retina
It is the light sensing layer composed of the retinal pigment epithelium and neural retina
30
Describe the vitreous humour/body
It is a transparent gel found in the back chamber of the eye
31
What is the Role of the vitreous humour/body ?
It provides the eyeball with structure
32
What is light focused by?
The corona and the lens
33
Where does the light go after being focused by the cornea and lens?
then passes through the vitreous humor to the retina.
34
Describe the path of light before hitting the retina
1. cornea
2. Lens
3. vitreous humor
4. retina.
35
Where are the photoreceptors found?
At the back of the retina
36
Describe the path light takes once it reaches the retina
1. Ganglion cell layer
2. Inner plexiform layer
3. Inner nuclear layer
4. Outer plexiform layer
5. Outer nuclear layer
6. Layer of photoreceptors
37
How may layers make up the retina
10
38
Name the 10 layers that make up the retina
1. Internal limiting membrane
2. Nerve fibre layer
3. Ganglion cell layer
4. Inner plexiform layer
5. Inner nuclear layer
6. Outer plexiform layer
7. outer nuclear layer
8. external limiting membrane
9. photoreceptors
10. Retinal pigment epithelium
39
Name the 1st layer of the retina
The retina pigment epithelium
40
Describe the retina pigment epithelium
is a single layer of cuboidal pigment cells that are tightly attached to each other providing part of the outer blood–retinal barrier.
41
What do the retina pigment cells contain?
Melanin
42
What does the melanin in retina pigment epithelium cells do?
It absorbs light that was not absorbed by the neural retina
43
Name the second layer of the retina
The photoreceptors
44
What does the photoreceptor layer contain?
The photo receptor cells:
| The rods and cones
45
Name the 3rd layer of the retina
The external limiting membrane
46
What is the external limiting membrane?
It is the junction between the apical processes of the Müller cells and the inner segments of the photoreceptor cells
47
Name the 4th layer of the retina
outer nuclear layer
48
What does the outer nuclear layer contain?
contains the photoreceptors nuclei and cell bodies.
49
Name the 5th layer of the retina
outer plexiform layer
50
What is the outer plexiform layer composed of?
composed of the synapses of the photoreceptor cells with the biopolar cells and the horizontal cells.
51
Name the 6th layer of the retina
inner nuclear layer
52
What does the inner nuclear layer consist of?
consists of the nuclei and cell bodies of the Müller, bipolar and amacrine cells
53
Name the 7th layer of the retina
inner plexiform layer
54
What is the inner plexiform layer, the site of?
is the site of the synapses between the bipolar cells and ganglion cells
It is also the site of action of the amacrine cells.
55
Name the 8th layer of the retina
ganglion cell layer
56
What does the ganglion cell layer contain?
Ganglion cell bodies
57
Name the 9th layer of the retina
nerve fibre layer
58
What is the nerve fibre layer made up of?
and is made of the axons of the retinal ganglion cells as they travel across the vitreous surface before leaving the eye through the optic nerve.
59
Name the 10th layer of the retina
The inner limiting membrane layer
60
What is the inner limiting membrane layer composed of?
is composed of the basal lamina from the Müller cell projections
61
Name the 2 types if photoreceptors
Cones
| Rods
62
Describe our cones
They have a colour system and work well in daytime
63
Describe our rods
They have no colour but work well in low light levels
64
Where does the process of absorption occur?
In the outer segments of the photoreceptors
65
What does the outer segment of the photoreceptors contain?
contains a stack of membranous disks which contain the light sensitive photopigments.
66
Describe the shape of rod photoreceptors
They have a long, cylindrical outer segment containing many disks,
67
Describe the shape of cone photoreceptors
They have a short, tapering outer segment with few membranous disks.
68
What do photoreceptors do?
They transduce light energy into change in membrane potential
69
Name some retinal cells
1. Horizontal cells
2. Bipolar cells
3. Amacrine cells
4. Ganglion cells
5, Müller cells
70
What do retinal cells do?
They do the ‘pre-processing’ before sending the visual information through the optic nerve
71
What is each photoreceptor in synaptic contact with?
2 types of retinal neurones:
| Bipolar cells and horizontal cells
72
What do bipolar cells do?
They create the direct pathway from photoreceptors to the ganglion cells
73
What do horizontal cells do?
They feed information laterally in the outer plexiform layer to influence neighbouring cells
74
What do amacrine cells do?
They control and modulate the majority of inputs to the retinal ganglion cells and the ganglion cell responses
75
Name the major glial cells of the retina
The Müller cells
76
Where are the Müller cells located?
In the neuronal retina and they span the entire depth
77
What do the Müller cells do?
Müller cells ensheath all retinal neurons and contribute significantly in mediating their functions and stability
78
Where do all the nerves of the retinal ganglion cell leave the retina from?
The optic nerve head
79
What is special about the fovea?
There are no blood vessels there and all the retinal cells have been pushed to the side to allow light to hit the photoreceptors more easily
80
Why are there no blood vessels in the fovea?
Because this the area where all out high acuity vision is done
81
Which photoreceptors do the fovea contain?
Only contains cones (V few rods)
82
Where are the majority of the rods found?
In the temporal and nasal retina
83
Where does the number of photoreceptors decrease?
As you get to the periphery
84
Where is our blind spot?
Where we have our optic disk
85
What is the pigment in all rods called?
Rhodopsin
86
How many types of opsins are there In cones?
3:
Red
Green
Blue
87
What is colour perception determined by?
Colour perception is determined by the relative contribution of the blue, green and red cones to the retinal signal.
88
What is colour blindness?
Is the inability to see colour or perceive colour differences
89
What is colour deficiency?
Is the decreased ability to see colour or perceive colour differences
90
What is total colour blindness called?
Achromatopsia
91
How common is Achromatopsia?
It is rare affecting 3/100,000
92
What causes Achromatopsia?
is caused by genetic mutations which result in only rod photoreceptors being functional.
93
What do patients with Achromatopsia see?
Affected patients see no colour but also have poor vision in bright light due to the sensitivity of the rod photoreceptors (one photon activates a response). They also have poor visual acuity due to lack of cones.
94
What is Dichromacy?
When One of the three basic colour mechanisms is not functioning
95
Name the 3 types of Dichromacy
1. Deuteranopia (mutation of green opsin)
2. Protanopia (mutation of red opsin)
3. Tritanopia (mutation of blue opsin)
96
Which od the 2 types of Dichromacy are x linked?
1. Deuteranopia (mutation of green opsin)
| 2. Protanopia (mutation of red opsin)
97
Who is more predominantly affected by red- green deficiency?
Males due to X-linked inheritance. The red and green opsin genes are on the X-chromosome.
5% of men have mutant green opsin and 1% have mutant red opsin.
98
What is the test that we use to check colour blindness called?
Iskikara test
99
What is Phototransduction?
It is the process by which light is converted into electrical signals in the rod and cone cells.
100
What are the photo pigment proteins (rhodopsin and opsins)
They are G- protein coupled receptors which are chemically attached to a vitamin A derived chromophore
101
What are rhodopsin and opsin attached to
chemically attached to a vitamin A derived chromophore called 11-cis retinal
102
Describe the phototransduction pathway
Light photons strike the chromophore and cause a conformational change to all-trans retinal.
This isomerization triggers the visual process by activating a signal transduction cascade.
103
What happens when a photon of light activates an 11-cis-retina?
It changes it to all-trans–retinal
104
Describe all-trans–retinal
They are not photosensitive to the opsin
105
What is the visual cycle?
All-trans-retinal are not photosensitive so the opsin must release this chromophore and replace it with more 11-cis-retinal. This process is called the visual cycle.
106
Go through the visual cycle
1. 11 cis retinol
2. converted into 11 cis retinal by enzyme 11 CIS RETINOL DEHYDROGENASE
3. converted into visual pigments
4. converted into all trans retinal when light hits the visual pigment
5. Converted into all trans retinol by enzyme ALL TRANS RETINOL DEHRIGENASE/REDUCATASE
6. connverted into retinal esters by enzyme LECIUTHIN RETINUL ACYLTRANSFERASE
7. Converted into 11cis retinol by enzyme RETINOIS ISOMEROHYDROLASE
107
Name the molecules involved in the visual cycle
1. 11 cis retinol
2. 11 cis retinal
3. Visual pigment
4. All trans retinal
5. all trans retino
6. Retinyl esters
7. 11 cis retinol
108
What does the enzyme 11 cis retinol dehydrogenase do?
Converts 11 cis retinol into 11 cis retinal
109
What does the enzyme all trans retinol dehydrogenase/ reductase do?
Converts all trans retinal into all trans retinol
110
What does the enzyme lectin retinol acyltransferase do?
Converts all trans retinol into retinyl esters
111
What does the enzyme retinoid isomerohydrolase do?
Converts retinal esters into 11 cis retinol
112
What can the consequences of one of the proteins in the visual cycle being mutated?
Can lead to inherited blindness
113
Describe the signal transduction process in photoreceptors
1. Guanosine diphosphate (GDP)-bound inactive transducin will exchange GDP for guanosine triphosphate (GTP) following interaction with activated rhodopsin.
2. The activated GTP-bound α-subunit of transducin dissociates and activates cyclic guanosine monophosphate (cGMP) phosphodiesterase (PDE).
3. PDE hydrolyzes cGMP to 5’GMP. The result is decreased levels of cGMP in the cytoplasm. This causes the closing of cGMP-gated ion channels leading to membrane hyperpolarization.
4. In photoreceptors, the neurotransmitters are released in depolarized membranes (dark light).
114
Where in the eye is there a really high pixel density?
In the fovea
115
A single photo activated rhodopsin catalyses the activation of approximately how many transduction molecules?
500 approx
116
Describe the 5 main features of rods
1. High sensitivity to light
2. Have more photopigment that cones
3. High amplification
4. Low temporal resolution and slower response
5. More sensitive to scattered light
117
Describe the 5 main features of cones
1. Low sensitivity to light (specialised for day vision)
2. Have less photopigment that rods
3. Low amplification
4. High temporal resolution and faster response
5. More sensitive to direct light rays
118
Does the rod system have a high or low acuity?
Low
119
Where in the retina are rod not present?
The Fovea
120
How may pigments does the rod system have?
1 so it is described as achromatic
121
Does the cone system have a high or low acuity?
High
122
How may pigments does the rod system have?
3 so it is described as trichromatic
123
How are our photoreceptor cells arranged in the retina?
They are set up in receptive fields
124
Take through the structures involved in the visual pathway
1. Retina
2. Optic nerves
3. Optic chiasm
4. Optic tract
5. Lateral geniculate nuclei
6. Optic radiations
7. Visual cortex
125
Where is the visual cortex?
The occipital lobe
126
Name the first region of visual processing in the cortex
The striate cortex
