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The Somatosensory System: Vision Flashcards

1
Q

What is the visual system made up of?

A

A coordinated pair of eyes, appropriate protective mechanisms, and the necessary neural apparatus to interpret visual information

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2
Q

What is the overall aim of the visual system?

A

To allow us to perceive the world around us.

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3
Q

What does the retina being able to form a focused image depend on?

A

It depends on the ocular shape, transparency of the ocular media, the ability of transparent structures to refract light, the transduction of light energy to electrical energy, and the integration of visual information from both eyes.

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4
Q

What are the physiological processes of vision divided into?

A

Light sense, colour sense, and form sense.

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5
Q

What is the light sense?

A

The ability to detect the presence and intensity of light, requiring chemical changes in photoreceptors.

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6
Q

What is the colour sense?

A

The ability to perceive different colours due to four pigment types in the retina.

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7
Q

What is the form sense?

A

The ability to discriminate and interpret different parts of the visual image by analyzing contours and contrast.

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8
Q

How do we integrate information collected by our eyes?

A

It requires mechanisms that enable the two eyes to move and work as a single functional unit, dependent on extraocular muscles and control of eye movements.

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9
Q

What do two eyes with good vision allow for?

A

Binocular vision, which enhances visual field perception and depth perception.

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10
Q

What is the caruncle and where is it?

A

A small, pink, globular spot (fold of tissue) that is always medial.

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11
Q

How many lids do we have?

A

We have an upper and lower lid with lashes.

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12
Q

What is the iris?

A

The coloured part of the eye that controls the size of the pupil.

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13
Q

What is the main barrier of the eye to the outside world?

A

The cornea, which provides 2/3 of the eye’s refracting power.

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14
Q

What are the anterior and posterior segments of the eye?

A

The anterior segment is before the lens, and the posterior segment is behind the lens.

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15
Q

What is the pupil?

A

The black dot in the center of the eye, a hole through which light passes to reach the retina.

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16
Q

What is the white part of the eye and what sits on top of it?

A

The sclera, with the conjunctiva sitting on top.

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17
Q

What sits in front of the iris and pupil?

A

The cornea.

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18
Q

What is the cornea?

A

A clear dome-shaped tissue that forms a barrier to the external environment and is responsible for 2/3 of the eye’s refractive power.

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19
Q

Where is the lens and what is it responsible for?

A

The lens sits behind the iris and fine-tunes the light angle, responsible for 1/3 of the eye’s refractive power.

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20
Q

What is behind the lens?

A

The posterior segment of the eye, filled with vitreous jelly.

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21
Q

What is the retina, and what is at its center?

A

The retina is the light-sensitive tissue lining the inner surface of the eye, with the macula at its center providing detailed vision.

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22
Q

Where does the optic nerve pass through?

A

The optic nerve leaves the eye and passes through the orbit into the brain.

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23
Q

What are the structures in the back of the eye?

A

The optic disc, which is the exit point of the optic nerve, and the macula, which provides detailed vision.

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24
Q

What are the retinal arteries?

A

Superior temporal, superior nasal, inferior temporal, and inferior nasal.

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25
How do retinal arteries differ from veins?
Retinal veins are thicker and darker than arterioles.
26
What are the two types of extraocular muscles?
Rectus muscles and oblique muscles.
27
What are the six extraocular muscles of the eye?
Superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique, and inferior oblique.
28
What is the innervation of the extraocular muscles?
LR6 SO4: CNVI innervates lateral rectus, CNIV innervates superior oblique, and CNIII innervates the remaining muscles.
29
What is 3rd cranial nerve palsy?
A condition where CNIII is impaired, leading to a down and out pupil, ptosis, and limited eye movement.
30
What is 4th cranial nerve palsy?
A condition causing vertical diplopia due to impairment of CNIV, affecting the superior oblique muscle.
31
What is 6th cranial nerve palsy?
A condition where CNVI is impaired, leading to difficulty abducting the eye and double vision when looking left.
32
What happens when trying to look left with impaired lateral rectus on the left side?
The right eye adducts, but the left eye does not abduct, leading to double vision when looking left.
33
What are the causes of cranial nerve palsies?
1. Microvascular diseases (CVA/ischaemia) 2. Compressive lesions (Aneurysms/tumours) 3. Inflammation (Sarcoidosis/GCA) 4. Demyelination (MS).
34
How many layers are in the retina and what is its role?
The retina has 10 layers of different cell types and converts light energy into nervous impulses.
35
What does the retina contain?
The retina contains 120 million rods and 6 million cones.
36
What is the role of photoreceptors in the retina?
Photoreceptors convert light energy into electrical energy.
37
Which cells modulate the transmission of information in the retina?
Horizontal and amacrine cells.
38
Which cells generate action potentials in the retina?
Ganglion cells generate action potentials.
39
What are the two types of photoreceptors and their gross structure?
1. Rods: 1 opsin called rhodopsin, sensitive in low light. 2. Cones: 3 opsins (red, green, blue), provide color vision.
40
What do we find in the peripheral retina?
Rods provide high sensitivity but low discriminatory non-color vision.
41
What is the central retina?
The central retina (macula and fovea) has the greatest density of cones and allows for high visual acuity.
42
Where is the macula located?
The macula lies lateral and slightly inferior to the optic disc.
43
How does the macula compare to the rest of the retina in color?
The macula is slightly darker than the rest of the retina due to the presence of yellow luteal pigment.
44
What is the center of the macula?
The fovea is the center of the macula and is completely rod-free.
45
What does the graph of rod vs cone density show?
The density of rods decreases and cones increases as you move from the peripheral retina to the fovea.
46
What is an OCT scan of the macula?
An OCT scan provides real-time images of the retina, showing different layers and the thinning of the retina approaching the fovea.
47
What occurs in rod photoreceptors under dark conditions?
cGMP-gated channels remain open, leading to Na+ influx and depolarization of photoreceptors.
48
What happens in rod photoreceptors under light conditions?
Light causes retinal to change shape, activating transducin and leading to hyperpolarization of the photoreceptor.
49
Describe the direct pathway of transmission through the retina.
Electrical energy travels from photoreceptor to bipolar cell to ganglion cell.
50
What are the two classes of bipolar cells?
1. ON Bipolar cells (depolarized in light) 2. OFF Bipolar cells (hyperpolarized in light).
51
What is a receptive field?
A receptive field is the region of the retina that influences a bipolar or ganglion cell.
52
What is the difference between direct and indirect pathways with photoreceptors?
Direct pathways involve direct connections, while indirect pathways involve horizontal/amacrine cells affecting responses.
53
What is macular degeneration?
Disruption of normal retinal structure leading to distortion/loss of central vision and reduced visual acuity.
54
How do retinal fibers travel out of the eye and into the brain?
The optic nerve is the route for retinal nerve fibers, containing over 1 million fibers.
55
Which nerve fibers in the eye are myelinated?
Nerve fibers are myelinated only after leaving the eye.
56
What is the optic disc?
The optic disc is the exit point of the optic nerve from the eye.
57
What are retinal nerve fibres?
Retinal nerve fibres exit the eye and enter the brain. It contains over 1 million fibres.
58
Which nerve fibres in the eye are myelinated?
Nerve fibres are myelinated only after leaving the eye.
59
What is the pathway of nerve fibres in the eye?
Nasal fibres decussate at the optic chiasm, whereas fibres from the temporal retina don’t decussate and stay on the same side of the brain.
60
What is the optic disc?
The optic disc is the exit of the optic nerve from the eye (1.5 x 1.5 mm) and corresponds to the blind spot of the visual field as it does not contain any overlying photoreceptors.
61
Describe a healthy optic nerve.
A healthy optic nerve has a pinkish colour and contains a cup, which is a space through which blood vessels travel within the nerve to enter the eye.
62
What is glaucoma?
Glaucoma is a raised intra-ocular pressure that results in increased pressure on the optic disc and optic nerve, leading to ischaemic tissue damage and structural changes to the optic nerve head.
63
What are the effects of glaucoma?
Glaucoma results in loss of retinal nerve fibres, making areas of the retina less sensitive to light, leading to progressive and irreversible loss of visual field.
64
What is the optic tract?
The optic tract extends from the optic chiasm to the lateral geniculate nucleus (LGN) and contains uncrossed and crossed fibres from the temporal and nasal retinas respectively.
65
What does the lateral geniculate nucleus (LGN) contain?
The LGN contains uncrossed and crossed fibres from the temporal and nasal retinas respectively, with about 30% of the fibres leaving the visual pathway before reaching the LGN.
66
What are optic radiations?
Optic radiations are formed by axons of the third neuron of the visual pathway originating in the LGN and terminate in the visual cortex.
67
Where does the primary visual cortex lie and extend to?
The primary visual cortex (Brodman's area 17) lies in the interhemispheric fissure and extends posteriorly about 1-2 cm onto the posterior surface of the cortex.
68
What happens in the visual cortex?
In the visual cortex, the inferior retina is projected into the superior visual field and vice versa, allowing for the re-inversion of images formed on the retina.
69
What is decussation?
Decussation refers to the crossing of nerve fibres at the optic chiasm, where the nasal retina of one eye crosses to the opposite side of the brain.
70
What is intracranial pathology?
Intracranial pathology refers to visual field defects that depend on the location of the pathology, such as loss of vision in one eye indicating pathology before the decussation in the optic chiasm.
71
What conditions can cause visual field defects?
Conditions that can cause visual field defects include CVA, space-occupying lesions (SOL), and multiple sclerosis.

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