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Mahathi Neurology > 1b Visual System > Flashcards

1b Visual System Flashcards

1
Q

What is the palpebral fissue?

A

The line of the eye where the eyelashes sit

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2
Q

What is the limbus?

A

The border between the cornea and the slcera?

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3
Q

What is the caruncle?

A

The inner most fleshy corner part of the eye

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4
Q

What is the medial canthus?

A

Where the caruncle meets the sclera

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5
Q

What neurotransmiter controls the release of tears?

A

Acetylcholine

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6
Q

Where are tears produced?

A

Lacrimal gland

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7
Q

Where are tears drained from?

A

Puncta - opens on the medial lid margin

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8
Q

What do the tears flow through in order to gather in the tear sac?

A

Gather in the tear sac

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9
Q

How to the tears exit the tear sac?

A

Through the tear duct - into the nasal cavity

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10
Q

What is the function of the tear film?

A

Maintains smooth cornea-air surface and regulates the oxygen supply to the cornea - as the normal cornea has no blood supply

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11
Q

What are the secondary functions of the tear film?

A

Bactericidal properties
Removal of Debris - through tear film and blinking

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12
Q

What are the three layers of the tear film called?

A

Most superficial = Lipid Layer
Water layer
Mucinous Layer

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13
Q

What is the function of the superficial lipid layer?

A

Reduce tear film evapouration

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14
Q

What is the lipid layer of the tear film produced by?

A

Meibomian glands

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15
Q

what is the water layer of the tear film do?

A

Thickest layer so acts as a lubricant

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16
Q

What is the role of the mucinous layer of the tear film?

A

Maintains surface wetting and keeps the tear on the eye

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17
Q

What is the conjunctiva?

A

Thin, transparent tissue which covers the outer surface of the eye

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18
Q

What are the three layers of the eye?

A

Sclera - hard and opaque
Choroid - pigmented and vascular
Retina - Neurosensory tissue

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19
Q

What is the sclera?

A

The white of the eye - tough and opaque tissue which serves as the eyes protective outer coat

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20
Q

What is the water content of the sclera?

A

High

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21
Q

What is the cornea?

A

The transparent, dome-shaped window covering the front of the eye.

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22
Q

What is the water content of the cornea like?

A

Low water content

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23
Q

What is the function of the cornea?

A

Powerful refracting surface, providing 2/3 of the eye’s focusing power. Like the crystal on a watch, it gives us a clear window to look through

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24
Q

What are the five layers of the cornea?

A

1 – Epithelium
2 – Bowman’s membrane
3 – Stroma – its regularity contributes towards transparency
4- Descemet’s membrane
5- Endothelium – pumps fluid out of corneal and prevents corneal oedema

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25
Q

What happens if the cornea becomes hydrated?

A

becomes cloudy

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26
Q

What is the uvea?

A

Vascular coat of eyeball and lies between the sclera and retina.

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27
Q

What are the three parts of the uvea called?

A

Composed of three parts – iris, ciliary body and choroid.

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28
Q

What is the choroid?

A

Choroid - lies between the retina and sclera. It is composed of layers of blood vessels that nourish the back of the eye.

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29
Q

What is the function of the iris?

A

Controls the amount of light which is entering into the eye - has tiny muscles which dilate and constrict the eye

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30
Q

What is the structure of the lens?

A

It is composed of an outer acellular thin capsule,
encasing a core of regular elongated cell fibres.

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31
Q

What percentage of the eyes refractory power comes from the lens?

A

1/3 of the eye focusing power - higher refractive index than aqueous fluid and vitreous

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32
Q

What is a cataract?

A

The lens may loose its transparency with age,
resulting in an opaque lens, known as Cataract.

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33
Q

What is the retina?

A

Thin layer of tissue which lines the inner part of the eye

Responsible for capturing the light rays which enter into the eye - light impulses are then sent to the brain for processing via the optic nerve

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34
Q

What is the function of the optic nerve?

A

Transmits electrical impulses from the retina to the brain

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35
Q

What is the visible portion of the optic nerve called?

A

The optic disc

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36
Q

Where does the optic nerve connect to the back of the eye?

A

Near the macula

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37
Q

What is the blind spot?

A

Where the optic nerve meets the retina, there are no light sensitive cells

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38
Q

What is the macula?

A

A small and highly sensitive part of the retina responsible for detailed central vision - located roughly in the centre of the retina

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39
Q

what is the structure found at the center of the macula?

A

Fovea

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40
Q

Which part of the eye allows us to perform tasks which require central vision like reading?

A

Fovea

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41
Q

What is the concentration of cones and rods like in the fovea?

A

Cones are high, rods and low

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42
Q

Why is the fovea particularly important?

A

Only the fovea has the highest concentration of cones in order for us to perceive high detail

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43
Q

What is the anatomical land mark for the physiological blind spot?

A

Optic disc

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44
Q

What is central vision?

A

Detailed, day vision - only the fovea

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45
Q

what is peripheral vision for?

A

Shape, movement and night vision, as well as navigation

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46
Q

What is the result of extensive loss of visual field?

A

Unable to navigate in an unfamiliar environment,

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47
Q

What is found in the outer layer of the retina?

A

Photoreceptor cells - involved in the detection of light

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48
Q

What is found in the middle layer of the retina?

A

Bipolar cells (2nd order neurones)

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49
Q

What is the function of the bipolar cells?

A

Local signal processing to improve contrast sensitivity

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50
Q

What does the inner layer of the retina contain?

A

Retinal ganglion cells (3rd order neurones)

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51
Q

What is the function of the retinal ganglion cels

A

Transmission of signal from the eye to the brain

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52
Q

What is the structural differences between the cones and the rods?

A

Rods = Longer outer segment
Cones = Shorter outer segment

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53
Q

What is the difference between rods and cones?

A

Rods = More sensitive to light, but slower response
Cones = Less sensitive to light, but faster response

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54
Q

Which photoreceptor cell is responsible for day light fine vision and colour?

A

Cones

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55
Q

Which photoreceptor cells is responsible for night vision?

A

Rods

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56
Q

What is scotopic vision?

A

Peripheral and night vision

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57
Q

Where can one find the highest concentration of Rod photoreceptors in the retina?

A

20-40 degrees away from fovea

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58
Q

Which cones are used for blue?

A

S-Cones

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59
Q

Which cones are used for Green?

A

M-Cones

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60
Q

Which cones are used for Red?

A

L-Cones

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61
Q

What colour are rods sensitive to?

A

Rods are used for night vision and spatial recognition and are not really sensitive to any particular colour

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62
Q

What is dueteranomaly, or Daltonsim?

A

most common type of colour blindness - red colourness

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63
Q

What is achromatopsia?

A

Full colour blindness

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64
Q

What is the name of the colour blindness test?

A

Ishihara test

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65
Q

what is refraction?

A

Then light goes from one’s medium to another, it changes velocity

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66
Q

What is the index of refraction and how is it calculated?

A

Ratio of speed of light in a vacuum to speed of light in a medium

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67
Q

What can the index of refraction be used for?

A

Help identify a material

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68
Q

What happens to the path of light when it changes from one medium to another?

A

Path changes

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69
Q

What is the angle of incidence?

A

Equal to the angle of reflection, is the angle at which light is reflected off the new medium

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70
Q

What are the two types of lenses?

A

Concave and convex

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71
Q

What does a convex lens do to light?

A

Takes the light rays and brings to a single focal point

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72
Q

What does a concave lease do?takes light rays and spreads them out

A
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73
Q

What is an example of an application of a converging lens?

A

A camera

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74
Q

What is emmetropia?

A

Perfect eye - adequate correlation between the axial length and refractive power

Parallel light rays fall on the retina without the need for accomodation

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75
Q

What is ametropia?

A

Mismatch between axial length and refractive power so parallel light rays do not fall onto the retina

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76
Q

What is myopia?

A

Near sightedness

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77
Q

What is hyperopia?

A

Far sightedness

78
Q

Where do the light rays converge in myopia?

A

Parallel rays converge at a focal point which is anterior to the retina - in front of it

79
Q

What are the causes of myopia?

A

Excessive long globe and excessive refractive power

80
Q

What are the symptoms of myopia?

A

Blurred distant vision
Squinting to attempt to improve visual activity
Headaches

81
Q

What are the treatments for myopia?

A

Diverting lens in glasses
Contact lenses
Refractive lens surgery

82
Q

What is hyperopia?

A

Parallel rays converge at a focal point posterior to the retina
Etiology : not clear, inherited Causes

83
Q

What are the causes of hyperopia?

A

•excessive short globe (axial hyperopia) : more common
•insufficient refractive power (refractive hyperopia)

84
Q

What are the symptoms of hyperopia?

A

visual acuity at near tends to blur relatively early
• nature of blur is vary from inability to read fine print to near vision is clear but suddenly and intermittently
blur
• blurred vision is more noticeable if person is tired , printing is weak or light inadequate
• asthenopic symptoms : eyepain, headache in frontal region, burning sensation in the eyes, blepharoconjunctivitis
• Amblyopia – uncorrected hyperopia > 5D

85
Q

What are the asthenopic symptoms of hyperopia?

A

Eye pain
Headache
Burning sensation in eyes
Blepharoconjuctivitis

86
Q

What is amblyopia?

A

When there is an uncorrected hyperopia of more than 5D in one eye

87
Q

If a person has good reading vision, which condition do they have?

A

Hyperopia

88
Q

What type of lens is used in glasses to treat hyperopia?

A

Converging lens

89
Q

What is an astigmatism?

A

When the parallel rays come to focus in two focal lines,

90
Q

What is the cause of an astigmatism?

A

Refractive media is not spherical - refract differently along one meridian than along meridian perpendicular to it– >2 focal points (punctiform object is represent as 2 sharply defined lines)

91
Q

What are the symptoms of an astigmatism?

A

Headache
Eye pain
Distortion of vision
Head tilting and turning

92
Q

What is the treatment of a regular astigmatism?

A

Cylinder lenses with or without spherical lenses

93
Q

What is the treatment of an irregular astigmatism?

A

Rigid cylinder lenses, surgery

94
Q

What is the near response triad?

A

Three actions of the eye in order for adapt for near vision

Increase depth of field
Align both eyes towards a near object
Increase refractive power of lens for near vision

95
Q

What is pupillary miosis ?

A

Pupil constricts which increases the depth of field of the eye

96
Q

Which muscle is responsible for the contraction of the pupil?

A

Sphincter pupillae

97
Q

What is the benefit of a larger depth of optic field?

A

Eye is able to maintain clear forms over a certain range of viewing distances which relying on accomodation

98
Q

What is convergence?

A

When the eyes adduct medial,y at the same time to align the eyes towards a near object

99
Q

How does convergence occur?

A

Simultaneous contraction of the medial rectus extra ocular muscles from both eyes

100
Q

Which muscles allow for accomodation of the eye?

A

Circular ciliary muscles

101
Q

What does accomodation do?

A

Increases the refractive power of lens for near vision

102
Q

What is presbyopia?

A

Naturally occuring loss of accommodation onset from age 40
Distant vision is intact

103
Q

How is presbyopia corrected?

A

Corrected by reading glasses - increases refractive power of the eye

104
Q

Why does the lens lose its ability to accommodate?

A

Natural lens loses elasticity

105
Q

What is the treatment of presbyopia?

A

Convex lenses in near vision - reading glasses or bifocal

106
Q

What are the two types of optical correction?

A

Contact lenses
Intraocular lenses

107
Q

What is an intraocular lense?

A

Replacement of a cataract crystalline lens

108
Q

Why are intraocular lenses the best treatment for aphakia?

A

Avoid significant magnification and distortion caused by spectacle lenses

109
Q

What is aphakia?

A

Absense of crystallin lens

110
Q

What is the problem with intraocular len?

A

They are monofocal, so provides help for distance but patient will need some reading glasses for near by activity

111
Q

What are the surgical options for treatment of eye problems?

A

Keratorefractive surgery :RK, AK, PRK, LASIK, ICR, thermokeratoplasty
Intraocular surgery : clear lens extraction (with or without IOL), phakic IOL

112
Q

Describe the steps of surgical correction?

A

. . . . .
.
. .
Surgical correction
Pre operative eye
Initial cutting of corneal flap
Cutting of corneal flap
Flipping of corneal flap
Photorefractive treatment (laser)
Corneal stroma reshaped post laser
Corneal flap back in position Treatment completed

113
Q

What is clear lens extraction and an intraocular lens?

A

Remove the lens and then add an artificial ones - patient will still need reading glasses as they lose the ability to accommodate

114
Q

What is the visual pathway?

A

The visual pathway is the neurological pathway,
where by vision is converted to neurological impulses, to be transmitted from the eye to the visual cortex, the posterior part of the brain.

115
Q

Where do the cell bodies of the optic nerve originate?

A

The retina

116
Q

Where do the optic nerve from each eye, converge?

A

Optic chiasm

117
Q

What happens to the ganglion nerve fibres at the optic chiasm?

A

About half of the ganglion nerve fibres cross at the optic chiasma, and exit along the contra-lateral Optic Tract, while the remaining ganglion nerve fibres exit along the Optic Tract on the same side.

118
Q

Where do the ganglion nerve fibres synapse?

A

Lateral Geniculate nucleus

119
Q

What is the fourth order neurone in the visual pathway?

A

Optic radiation - takes information from the lateral geniculate ganglion to the primary visual cortex in the occipital lobe

120
Q

What cortex is involved in higher visual processing?

A

Extra-striate Cortex

121
Q

What are the first second and third order neurones of the retinal visual pathway?

A

First Order Neurons – Rod and Cone Retinal Photoreceptors
Second order Neurons – Retinal Bipolar Cells
Third Order Neurons –Retinal Ganglion Cells

122
Q

what happens to the retinal ganglion fibres after entering into the optic nerve?

A

become myelinated to improve signal transmission

123
Q

What type of visual defect do you get when you have a lesion which is anterior to the optic chiasm?

A

Lesions anterior to Optic Chiasma affect visual field in one eye only

124
Q

What type of visual defect do you get when you have a lesion which is posterior to the optic chiasm?

A

Lesion occurring posterior to the Optic Chiasma will affect visual field simultaneously in both eyes,
because of the fibre crossing at the chiasma.

125
Q

Where do the crossed fibres predominantly originate from?

A

predominantly originate from the nasal retina,
responsible for the temporal half of the visual field in each eye.

126
Q

Where do the uncrossed fibres predominantly originate from?

A

The uncrossed fibres predominantly originate from the temporal retina,
responsible for the nasal half of the visual field in each eye.

127
Q

Lesion at optic chiasm?

A

Bitemporal hemanopia - temporal field deficit in both eyes

128
Q

Lesions posterior to optic chiasm?

A

Right sided lesion – Left Homonymous Hemianopia in Both Eyes
Left sided lesion – Right Homonymous Hemianopia in Both Eyes

129
Q

What is the most common cause of bitemporal hemaniopia?

A

Typically caused by enlargement of Pituitary Gland Tumour

130
Q

What is the most common cause of homonymous hemianopia?

A

On the other hand, homonymous hemianopia is typically caused by stroke,
or cerebrovascular accidents in the brain.

131
Q

What does damage of the primary visual cortex lead to?

A

Homonymous Hemianopia with Macular Sparing

132
Q

Why is the macula spared in damage t the primary visual cortex?

A

Area representing the Macula receives dual blood supply from Posterior Cerebral Arteries from both sides

133
Q

What happens to the pupil in the light?

A

Constriction

134
Q

What nerve mediates pupillary constriction?

A

Parasympathetic nerve - within CNIII

135
Q

What causes the circular muscles to contract and what does this lead to?

A

parasympathetic stimulation - pupil constriction

136
Q

What causes the radial muscles to contract and what does this lead to?

A

Sympathetic stimulation - pupil dilation

137
Q

When does the pupil dilate?

A

In dark environments

138
Q

Why does the pupil constrict in light?

A

decreases spherical aberrations and glare
increases depth of field
reduces bleaching of photo-pigments

139
Q

Describe the efferent pathway of the pupillary reflex?

A

Edinger-Westphal Nucleus -> Oculomotor Nerve Efferent ->
Synapses at Ciliary ganglion ->
Short Posterior Ciliary Nerve -> Pupillary Sphincter

140
Q

Where do the afferent fibres of the pupillary reflex become the efferent?

A

Edinger-Westphal Nuclei

141
Q

What is the direct and consensual reflex?

A

Direct Light Reflex –Constriction of Pupil of the light-stimulated eye
Consensual Light Reflex – Constriction of Pupil of the other (fellow) eye

142
Q

What is the neurological basis of the direct and consensual reflex?

A

Afferent pathway on either side alone will stimulate efferent (outgoing) pathway on both sides

143
Q

What is the observed difference in afferent and efferent defects

A

In short, afferent defect produces different responses between eyes, depending on which eye is stimulated.

Efferent defect produces the same unequal responses between left and right eye, no matter whether left or right eye is stimulated.

144
Q

What is the swinging torch test?

A

Shining light between right and left rapidly

145
Q

What is a relative afferent pupillary defect?

A

When the damage to the afferent pathway is incomplete

146
Q

What is the best way to test the relatife afferent pupillary defect?

A

Swinging torch test

147
Q

Describe a positive swinging torch test for a relative afferent pupillary defect?

A

Both pupils constrict,
when light swings to the left eye with intact afferent pathway.

Both pupils will paradoxically dilate,
when the light swings to the right eye with damaged afferent pathway, as a result of relatively reduced drive for pupillary constriction in both eyes.

148
Q

What facilitates the movement of the eye?

A

It is facilitated by the six extraocular muscles in the orbit,
innervated by the three cranial nerves.

149
Q

What is duction?

A

Eye movement in one eye, without making any reference to the movement in the other eye

150
Q

What is version?

A

Simultaneous movement of both eyes in the same direction?

151
Q

What is vergence?

A

Simultaneous movement of both eyes in the opposite direction

152
Q

What is convergence?

A

Simultaneous adduction (inward) movement in both eyes when viewing a near object

153
Q

What is a saccade?

A

Short fast burst

154
Q

When might you use a saccade eye movement?

A

Reflexive saccade to external stimuli
Scanning saccade
Predictive saccade to track objects
Memory-guided saccade

155
Q

What is a smooth pursuit?

A

Smooth Pursuit is a slow sustain movement,
up to 60 degrees per second.

It is an involuntary movement,
driven by a moving target.

156
Q

What are the straight muscles of the eye called?

A

Superior rectus
Inferior rectus
Lateral rectus
Medial rectus

157
Q

What are the names of the two muscles of the eye which are not straight

A

Superior oblique
Inferior Oblique

158
Q

what does the superior rectus do to the eye?

A

Moves the eye up

159
Q

What does the inferior rectus do to the eye?

A

moves the eye down

160
Q

what does the lateral rectus do?

A

Moves the eye towards the outside of the head - towards temple

161
Q

What does the medial rectus do?

A

Moves the eye towards the midline

162
Q

Describe the action of the superior oblique?

A

Passes under the Superior Rectus.
Moves the eye in a diagonal pattern down and out

163
Q

Describe the action of the inferior oblique?

A

Moves the eye in a diagonal pattern - up and out.

164
Q

Which eye muscles are innervated by the superior branch of the third cranial nerve - occulomotor?

A

Superior Rectus – elevates eye
elevator palpebrae superioris - raises eyelid (not shown)

165
Q

Which eye muscles are innervated by the inferior branch of the third cranial nerve - occulomotor?

A

Inferior Rectus – depresses eye
Medial Rectus – adducts eye
Inferior Oblique – elevates eye
Parasympathetic Nerve – constricts pupil

166
Q

Which eye muscles are innervated by the fourth cranial nerve?

A

Superior oblique - depresses eyes

167
Q

Which eye muscles are innervated by the 6th cranial nerve?

A

Lateral Rectus – abducts eye

168
Q

What position of the eye best tests the lateral rectus?

A

Abduction

169
Q

What position of the eye best tests the medial rectus?

A

Adduction

170
Q

What position of the eye best tests the superior rectus?

A

Abducted and Elevated

171
Q

What position of the eye best tests the inferior rectus?

A

Depressed and abducted

172
Q

What position of the eye best tests the inferior oblique?

A

Elevated and adducted

173
Q

What position of the eye best tests the superior oblique?

A

Depressed and adducted

174
Q

what is supraduction and supraversion?

A

elevation of one eye, and elevation of both eyes

175
Q

What is infraduction and infraversion?

A

Infraduction – one eye
Infraversion – both eyes

176
Q

What is dextroversion?

A

Movement of the eyeballs to look at the right

177
Q

What is levoversion?

A

Movement of the eyes to look at the left

178
Q

What is torsion?

A

Torsion – rotation of eye around the anterior-posterior axis of the eye

179
Q

What does the eye look like in third nerve palsy?

A

affected eye is down and out

180
Q

How is the eyelid effected in third nerve palsy?

A

Droopy eyelid - due to loss of elevator palepbrae superioris

181
Q

Why does third nerve palsy result in a down and out movement of the eye?

A

Unopposed superior oblique innervated by fourth nerve (down)
Unopposed lateral rectus action innervated by sixth nerve (out)

182
Q

What does 6th nerve palsy result in?

A

patients are deficit in abduction in the affected eye

Affected eye will deviate inwards

183
Q

What is a nystagmus?

A

Oscillatory eye movement

184
Q

What is Optokinetic Nystagmus?

A

Smooth pursuit followed by a reset ot the eye position in the center with a burst of saccade movement

185
Q

What does presence of the opto-kinetic nystagmus show?

A

The presence of Opto-kinetic Nystagmus signifies that the subject has sufficient visual acuity to perceive the grating.

186
Q

What is the neurotransmitter of the lacrimal system?

A

Acetylcholine

187
Q

What is the role of the Meibomian glands?

A

secretes the lipid layer which protects the tear film from rapid evapouration

188
Q

How do mucin molecules affect the tear film?

A

they bind water molecules to the hydrophobic corneal epithelial cell surface

189
Q

Describe the synthesis of photo pigments

A
  1. discs with deactivated photo pigments are shedded from the tips and phagocytosed by the retinal epithelial cells
  2. deactivated photopigments are regenerated inside the retinal epithelial cells and transported by to the photo receptors
190
Q

What is asthenopia?

A

Eye strain condition which manifests through non-specific symptoms such as fatigue, pain in and around the eyes, blurred vision and occasional double vision

191
Q

What is the most common cause of homonymous hemaianopia?

A

Stroke of another cerebrovascular accidents of the brain

192
Q

Lesions posterior to what result in homonymous hemianiopia?

A

Posterior to the chiasma

Mahathi Neurology (22 decks)

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