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eLCRS - 뉴로 > Neuro 11: Structure + Function of the eye > Flashcards

Neuro 11: Structure + Function of the eye Flashcards

1
Q

Identify the anatomical components of the eye

draw eye + muscles

A

-

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2
Q

The eye sits in the _______

A

Orbit

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3
Q

The lacrimal system produces 3 types of tears :

A
  • basal tears
  • reflex tears
  • emotional tears
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4
Q

What are basal tears?

A
  • tears that are produced at a constant level

- -> even in absence of irritation/stimulation

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5
Q

What are reflex tears?

A
  • increased tear production in response to irritation
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6
Q

What is the tear reflex made up of?

A

made up of:

  • afferent pathway
  • CNS
  • efferent pathway
  • lacrimal gland
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7
Q

irritation of cornea = detected by sensory nerve fibres via _____________

A

irritation of cornea = detected by sensory nerve fibres via the ophthalmic branch of the trigeminal nerve (CN V)

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8
Q

efferent pathway = mediated by ______ nerve

–> which innervates the lacrimal gland

A

efferent pathway = mediated by a parasympathetic nerve

–> which innervates the lacrimal gland

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9
Q

tear films drain through the 2 ______

on the upper + lower medial lid margins

A

tear films drain through the 2 puncta

on the upper + lower medial lid margins

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10
Q

the puncta form the opening to the ____ and _____ ______

A

the puncta form the opening to the superior + inferior canliculi

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11
Q

the superior + inferior canaliculi converge –> as a single common canaliculus –> and this drains the tears into the ______

A

the superior + inferior canaliculi converge –> as a single common canaliculus –> and this drains the tears into the TEAR SAC

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12
Q

What is the function of the tear film?

A

tear film:

  • maintains a smooth cornea- air surface
  • important to maintain clear vision
  • important for removing surface debris during blinking
  • source of O2 + nutrient supply to anterior segment
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13
Q

What is a tear film?

A

tear film:

  • thin layer of fluid that covers the cornea
  • it is a bactericide
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14
Q

The Tear film consists of what 3 layers?

A
  • superficial oily layer
  • aqueous tear film
  • mucinous layer
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15
Q

What does the Superficial Oily Layer do?

and what produces it?

A
  • it reduces tear film evaporation

produced by: Meibomian Glands (along the lid margin)

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16
Q

What is the aqueous tear film?

what does it do?

A

Aqueous Tear film = main bulk of the tear film
–> contains bactericide

  • it delivers oxygen + nutrients to the surrounding tissue
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17
Q

What does the mucinous layer do?

A
  • it maintains surface wetting

- and ensures that the tear film sticks to the eye surface.

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18
Q

How do the mutinous layer work?

A
  • the mucin molecules act by binding water molecules to the hydrophobic corneal epithelial cell surface
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19
Q

What is the conjunctiva?

A

conjunctiva = thin transparent tissue that covers the outer surface of the eye

–> very vascularized

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20
Q

What special feature does the conjunctiva have?

A
  • it has goblet cells that produce mucin
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21
Q

What is the average anterior posterior diameter in adults?

A

24mm

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22
Q

What are the 3 layers that forms the coat of the eye?

A
  1. Sclera
  2. Choroid
  3. Retina
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23
Q

What are the characteristics of each layer that forms the coat of the eye?

  1. Sclera
  2. Choroid
  3. Retina
A
  1. Sclera
    - hard + opaque
  2. Choroid
    - pigmented + vascular
  3. Retina
    - neurosensory tissue
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24
Q

What is the sclera ?

A
  • white of the eye
  • tough opaque tissue that serves as the eye’s protective outer coat

–> it has high water content

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25
Q

What is the Cornea?

A

cornea = transparent, dome shaped window
that covers the front of the eye

  • it acts as a powerful refracting surface
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26
Q

What are main characteristics of the cornea

A
  • it is the front most part of the anterior segment
  • it is continuous with the scleral layer
  • transparent
  • provides 2/3 of eye’s focusing power
  • has physical + infection barrier
  • -> it has low water content
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27
Q

What are the 5 layers of the Cornea?

A
  1. Epithelium
  2. Bowman’s memb
  3. Stroma
  4. Descemet’s memb
  5. Endothelium
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28
Q

What is the significance of the stroma layer ?

A
  • regularity of stroma contributes towards transparency
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29
Q

What is the significance of the Endothelium?

A
  • it pumps fluid out of the corneal
  • and prevents corneal oedema

note:
- endothelial cell density decreases with age

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30
Q

What happens if you hydrate the cornea?

A

?????

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31
Q

What is the Uvea?

A

Uvea = vascular coat of eyeball that lies between the sclera + retina

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32
Q

What are the 3 parts that the uvea is composed of?

A
  • Iris
  • Ciliary body
  • Choroid
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33
Q

Where does the choroid lie?

A
  • lies between the retina + sclera
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34
Q

What is the IRIS?

and what does it do?

A
  • colored part of the eye
  • embedded with small muscles that dilate + constrict the pupil size
  • the iris controls light levels inside the eye
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35
Q

Describe the structure of the lens

A

Outer: has acellular capsule
inner: regular elongated cell fibres

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36
Q

What happens if the lens loses transparency with age?

A

cataract

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37
Q

What is the function of the lens?

A
  • provides transparency
  • has refractive power (responsible for 1/3 of refractive power of eye)
  • provides accommodation
  • -> through elasticity .
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38
Q

Lens = suspended by fibrous ring known as ___ _____

which consists if a passive connective tissue

A

Lens = suspended by fibrous ring known as lens zones

which consists if a passive connective tissue

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39
Q

What is the retina?

A
  • retina = thin layer of tissue that lines the inner part of the eyes
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40
Q

What is the retina responsible for?

A
  • responsible for capturing light rays that enter the eye

- the light impulses are then sent tp the brain for processing via the optic nerve

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41
Q

What is the function of the optic nerve?

A
  • optic nerve transmits electrical impulses from the retina to the brain

–> it connects to the back of the eye (near the macula)

42
Q

The visible part of the optic nerve = called the __________

A

optic disc.

43
Q

What is the blind spot ?

A
  • blind spot = where the optic nerve meets the retina

- -> there are no light sensitive cells

44
Q

Where is the macula located at?

A
  • located roughly at the centre of the retina, temporal to the optic nerve

-

45
Q

What is the macula?

what is its function?

A
  • small + highly sensitive part of the retina
  • which is responsible for detailed central vision (e.g reading)

FOVEA = very centre of macula (forms a pit)

46
Q

What is the difference between central vision + peripheral vision?

A

Central:
- provided detailed day vision / color vision
- for reading / facial recognition
- assed by visual activity assessment
Loss of Foveal vision –> leads to poor visual acuity

Peripheral:
- allows recognition of shape/ movement and night vision
- allows navigation vision
- assessed by visual field assessment
Loss of visual field –> leads to not being unable to navigate in environment

47
Q

Fovea has the highest conc of ___________

A
  • cone photoreceptors
48
Q

describe the organisation of the retinal layer

A

outer: photoreceptors
middle: bipolar cells
inner: retinal ganglion cells

49
Q

What are the 2 main classes of photoreceptors in the retina?

how do they differ in:

a) sensitivity to light
b) speed of response
c) night vision / daylight vision

A
  1. Rod photoreceptor
    - 100x more sensitive to light than cones
    - slower response
    - responsible for night vision
  2. Cone photoreceptor
    - less sensitive to light
    - faster response
    - responsible for day light fine vision + color vision
50
Q

Where can you find the highest conc of rod photoreceptors in the retina?

A
  • 20 to 40 deg away from fovea
51
Q

What is the Ishihara test?

A
  • it is a color perception test

- tests for red-green deficiencies only

52
Q

What is dark adaptation?

why is it a biphasic process?

A

Dark Adaptation:

  • increase in light sensitivity in the dark
  • it is a biphasic process
  • -> 7 mins cone adaptation
  • -> 30 mins rod adaptation
53
Q

What is light adaptation?

how does it occur?

A 
Light Adaptation: 
- adaptation from dark to light 
- occurs over 5 mins 
- involves bleaching of photo pigments 
- neuro adaptation 
-
54
Q

What is Pupil adaptation?

A
  • minor process

- that allows construction of pupil with light

55
Q

What is the most common form of color vision deficiency in humans?

A

red-green confusion

56
Q

How do you calculate Index of refraction?

A

n = speed of light in vacuum / speed of light in medium

57
Q

What are the 2 basic types of lenses?

A
  1. converging lens
    - -> which brings them to a single point
  2. Diverging lens
    - -> which takes light rates and spreads them outwards
58
Q

What is Emmetropia?

A
  • adequate correlation between axial length + refractive power
  • parallel light rays fall on the retina (no accommodation)
59
Q

What is Ametropia? (refractive error)

A
  • There is a mismatch btw axial length + refractive power

–> so parallel light rays don’t fall on the retina

60
Q

list 4 examples of ametropia

A
  • myopia
  • hyperopia
  • astigmatism
  • presbyopia
61
Q

What is the mechanism of myopia?

A
  • parallel rays converge at a focal point anterior to the retina
62
Q

What are 2 main causes of myopia?

A
  1. excessive long globe (axial myopia) - common

2. excessive refractive power

63
Q

What are symptoms of myopia?

A
  • blurred distance vision
  • squinting to improve uncorrected visual activity when gazing into distance
  • headache
64
Q

What is the mechanism of hyperopia?

A
  • parallel rays converge at focal point posterior to the retina
65
Q

What are 2 main causes of hyperopia?

A

1 . excessive short globe - common

2. insufficient refractive power

66
Q

What are symptoms of hyperopia?

A
  • visual acuity at near –> blurs relatively early
  • has asthenopic symptoms (e.g eye pain, headache in frontal region, burning sensation in eyes)
  • amblyopia
67
Q

What is the mechanism of astigmatism?

A
  • parallel rays come to focus in 2 focal lines rather than a single focal point

–> usually due to heredity

68
Q

What is the main cause of astigmatism?

A
  • refractive media = not spherical

- -> light rays are refracted differently forming –> 2 focal points on the retina

69
Q

What are the main symptoms of astigmatism?

A
  • asthenopic symptoms
  • blurred vision
  • distorted vision
  • head tilting + turning
70
Q

How would you treat astigmatism ?

A

REGULAR ASTIGMATISM:
–> cylinder lenses w/wo spherical lenses

IRREGULAR ASTIGMATISM

  • -> rigid CL
  • -> surgery
71
Q

What are the near response triad?

A
  1. pupillary miosis
    - -> to increase depth of field
  2. convergence
    - -> to align both eyes towards a near object
  3. accommodation
    - -> to increase refractive power of lens for near vision
72
Q

What is presbyopia?

A
  • naturally occurring loss of accommodation
  • onset: from 40 years
  • distant vision = intact
73
Q

How would you treat presbyopia?

A
  • use convex lenses for near vision

e. g reading/bifocal/trifocal/progressive power glasses

74
Q

What are the different types of optical correction?

A
  1. spectacle lenses
  2. contact lenses
  3. intraocular lenses
  4. surgical correction
75
Q

compare adv + dsadv for the different methods of optical correction:

A

?????????????????????

76
Q

Describe the mechanism for accommodation

A
  1. contraction of circular ciliary muscle inside the ciliary body
  2. this relaxes the zones that are normally stretched between the ciliary body attachment + the lens capsule attachment
  3. in the absence of zonular tension –> lens returns to its natural shape
  4. this increases the refractive power of the lends

–> accommodation = mediated by the efferent 3rd cranial nerve

77
Q

Where do retinal ganglion axons coming down the optic nerve synapse?

A
  • Lateral geniculate nucleus
78
Q

Where is the lateral geniculate nucleus found?

A
  • Thalamus
79
Q

What are the fibres leaving the lateral geniculate nucleus called?

A
  • Optic radiation
80
Q

Describe the convergence and receptive field sizes of rods.

A
  • rods = have high convergence + large receptive fields
81
Q

Describe the convergence and receptive field sizes of cones.

A
  • cones = have low convergence + small receptive fields
82
Q
  1. What is the benefit of having high convergence and a large receptive field?
A
  • High light sensitivity
83
Q
  1. What is the benefit of having low convergence and a small receptive field?
A
  • Fine visual acuity
84
Q

which parts of the visual field is it responsible for?

a) upper division of the optic radiation

A
  • Responsible for inferior visual quadrant
85
Q

which parts of the visual field is it responsible for?

b) lower division of the optic radiation

A
  • Responsible for superior visual quadrants
86
Q
  • The left primary visual cortex = responsible for the right/left visual field from both eyes
  • ## The right primary visual cortex = responsible for the left/right visual field from both eyes
A
  • The left primary visual cortex = responsible for the right visual field from both eyes
  • The right primary visual cortex = responsible for the left visual field from both eyes
87
Q

Visual cortex above the calcarine fissure = responsible for the inferior / superior visual field

  • Visual cortex below the calcarine fissure = responsible for the superior / inferior visual field
A

Visual cortex above the calcarine fissure = responsible for the inferior visual field

  • Visual cortex below the calcarine fissure = responsible for the superior visual field
88
Q

How is it possible for the macula to be spared by a stroke in the primary visual cortex leading to homonymous hemianopia?

A

area representing macula in the primary visual cortex = has dual blood supply (from both right and left posterior cerebral arteries) –> so less vulnerable to ischaemia

89
Q

describe the pathway of consensual light reflex

A
  • Retinal Ganglion Cell –> Pretectal Nucleus –> Edinger-Westphal Nucleus –> Ciliary Ganglion –> Short Ciliary Nerves –> Sphincter Pupillae
90
Q

What test would you do to identify RAPD?

what is RAPD?

A

RAPD = Relative afferent pupillary defect

  • Swinging torch test
91
Q

What would you see in a patient with RAPD? in a swinging torch test?

A
  • When the light is shone on good eye –> there is direct and consensual response
  • When the light shone on bad eye –> there is paradoxical dilation of iris in bad eye
  • This is because there is weaker constriction response in the bad eye than the consensual response elicited by the good eye
92
Q

define - Dextroversion

A

right gaze

93
Q

define – Levoversion

A

left gaze

94
Q

define - Infraversion

A

depression of both eyes

95
Q

define- Supraduction

A

elevation of one eye

96
Q

What are the two types of eye movement

A
  • Saccade = short fast burst

- Smooth pursuit = sustained slow movement

97
Q

describe the innervation of extrinsic eye muscles

A

Lateral Rectus = Abducens (CN VI)
Superior Oblique = Trochlear (CN IV)
Medial Rectus, Superior Rectus, Inferior Oblique, Inferior Rectus and Levator Palpebrae Superioris = Oculomotor (CN III)

98
Q

Where do all the rectus muscles originate

A
  • Common tendinous ring at apex of orbit
99
Q

What would you see in a patient with 3rd nerve palsy?

A
  • Eye points down and out
  • Due to unopposed lateral rectus + superior oblique
  • Ptosis –> due to loss of innervation of lavatory palpebrae superioris
  • Pupil dilation –> due to loss of parasympa innervation to eye via oculomotor nerve
100
Q

What would you see in a patient with 6th nerve palsy?

A
  • When asked the abduct the affected eye, they eye will stop around midline
  • because the lateral rectus isn’t functioning and can’t abduct the eye
  • This can lead to blurred vision
101
Q

What is the function of Medial longitudinal fasciculus (MLF) ?

A

allows paired eye movements

102
Q

what can happen to the eyes when MLF is damaged ?

A
  • Internuclear opthalmoplegia

E.g. right abduction wont be accompanied by left adduction
- Could be accompanied by nystagmus on right gaze

eLCRS - 뉴로 (16 decks)

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