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Neuro > Neuro 12: Structure and function of the eye > Flashcards

Neuro 12: Structure and function of the eye Flashcards

1
Q

Which structures pass through:

  1. Sup. orbital fissure
  2. Optic foramen
  3. Supraorbital notch
  4. Infraorbital fissure
  5. Infraorbital groove
  6. Infraorbital foramen
A
  1. Trochlear, abducens, oculomotor (superior and inferior division) and ophthalmic (lacrimal, frontal and nasociliary branches of ophthalmic) cranial nerves, opthalmic vein (supoerior and inferior division)
  2. Optic nerve and ophthalmic artery
  3. supraorbital nerve (from frontal from opthalmic) and vessels (supraorbital artery and supraorbital vein.)
  4. Zygomatic branch of the maxillary nerve and the ascending branches from the pterygopalatine ganglion. Infraorbital vessels pass from here. Inferior division opthalmic vein
  5. Infraorbital vessels (infraorbital artery from the maxillary artery from external carotid) (through infraorbital groove, canal, and out via infraorbital foramen)
  6. Infraorbital vessels emerge and infraorbital nerve (branch of V2)
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2
Q

Corners of eye name

Normal AP diameter of eye

A

Lateral and medial canthas

Eye -Anterio-Posterior Diameter -24mm in adults

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3
Q

Name of pink bit on medial side of eye

A

Caruncle

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4
Q

What separates iris from sclera

A

Limbus

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5
Q

What is in the limbus

A

(corneal stem cells)

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6
Q

Function of tear film

A

Tear film maintains smooth cornea-air surface
Oxygen Supply to Cornea – Normal cornea has no blood vessels
Removal of Debris (Tear film and Blinking)
Bactericide
Maintaining clear vision

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7
Q

Where is the lacrimal gland located

A

In orbit, latero-superior to the globe, produces watery tears

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8
Q

Outline the reflex tear production

A

V1 opthalmic sensory, effernt is parasympathetic (CN7- acetycholine),`

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9
Q

Where to tears drain

A

Tear drains through the two puncta, opening on medial lid margin
Tear flows through the superior and the inferior canaliculi
Tear gathers in the Tear Sac
Tear exits the Tear Sac through the tear duct into the nose cavity (into inferior nasal meatus)

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10
Q

Why is pressure not releaved from puncta during sneezing

A

Valve in canaliculi (prevents retrograde reflux of fluid from the sac into the canaliculi)

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11
Q

3 layers of tear film

A

Lipid layer= meibum (superficial to reduce film evaporation, produced by Meibomian Glands along the lid margins)
Aqeuous (from tear gland)
Mucinous layer on corneal surface for surface wetting

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12
Q

How does the mucin layer work

A

The mucin molecules (produced by goblet cells) act by binding water molecules,
to the hydrophobic corneal epithelial cell surface.

(make it wettable)

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13
Q

Define conjunctiva

A

The conjunctiva is the thin, transparent tissue that covers the outer surface of the eye.

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14
Q

Where does conjunctiva extend

A

t begins at the outer edge of the cornea, covers the visible part of the eye, and lines the inside of the eyelids.

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15
Q

3 layers of the eye (from superficial to deep, at the back)

A

retina, choroid, sclera

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16
Q

What is the optic disk

A

surface manifestation of optic nerve

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17
Q

Characterise sclera, choroid and retina

A

Sclera – Hard and Opaque (protective outer coat)
Choroid – Pigmented and Vascular
Retina – Neurosensory Tissue

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18
Q

Which layer surrounds the optic nerve

A

retina

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19
Q

Compare water content of sclera and cornea

A

sclera- high cornea- low

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20
Q

What is cornea

A

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

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21
Q

What is the front most part of anterior semgnet

A

cornea

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22
Q

Which layer of eye is cornea continuous with

A

Sclera

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23
Q

What is the survature of cornea

A

Convex

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24
Q

Why is cornea refractive

A

Convex curvature

Higher refractive index than air

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25
Q

Other function of cornea other than refraction

A

Physical Barrier

Infection Barrier

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26
Q

5 layers of cornea

A 
1 – Epithelium 
2 – Bowman’s Membrane
3 – Stroma – regularity contributes towards transparency
4- Descements membrane
5. Endothelium

Epstein Bar Sung Down Eltham

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27
Q

What contributes to corneal transparency

A

Regularity of stroma

And the lack of water because endothelial cells pump it out

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28
Q

What is and is not present in stroma

A

is- corneal nerve endings providing sensation and nutrients for healthy tissue

Is not- blood vessels

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29
Q

What does endothelium of the cornea do

A

pumps fluid out of corneal and prevents corneal oedema,

1 layer

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30
Q

Why, with age, can you get corneal oedema and cloudiness

A

Endothelial layer pumps water from the more superifical stromal layer

Only 1 layer of endothelial cell, and they have no regeneration power

Endothelial cell density decreases with age

Endothelial cell dysfunction may result in corneal oedema and corneal cloudiness

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31
Q

What happens if you hydrate hte cornea

A

It goes opaque

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32
Q

What is the uvea

A

Vascular coat of eye ball

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33
Q

In which layers does the uvea lie

A

lies between the sclera and retina.

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34
Q

3 parts of the uvea

t/f all parts of the uvea are intimately connected, so a disease of one part affects all parts

A

Iris
ciliary body
choroid.

T, though not necessarily to the same degree.

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35
Q

What nourishes the outer and inner part of the retina

A

Outer part: choroid

Inner part: central radial artery

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36
Q

Define iris

A

coloured part of the eye

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37
Q

What controls light levels inside eye

A

iris (embedded with tiny muscles that dilate (widen) and constrict (narrow) the pupil size. )

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38
Q

What is responsible for refractory power of the eye

A

2/3- cornea

1/3 lens

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39
Q

structure of lens

A
  1. Outer Acellular Capsule

2. Regular inner elongated cell fibres – transparency

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40
Q

Functiion of lens

A
  1. Transparency
    -Regular structure
  2. Refractive Power
    -1/3 power
    -Higher refractive index than aqueous fluid and vitreous
  3. Accommodation
    Elasticity
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41
Q

What is cataracts

A

Lens loose transparency with age

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42
Q

What is the lens zonules

A

Lens is suspended by a fibrous ring known as lens zonules, consists of passive connective tissue

Anchors lens to ciliary body

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43
Q

What allows focusing

A
  1. Action of ciliary muscle on lens

2. Iris aperture

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44
Q

What is the blind spot

A

Where the optic nerve meets the retina there are no light sensitive cells. It is a blind spot.

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45
Q

Where is the macula vs optic disk

A

Macula=roughlyin centre, temple to optic nerve(dark)

Optic disc=nasal side

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46
Q

The optic nerve contains axons, from which cell body

A

The retinal ganglion cells

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47
Q

What is the macula responsible for

A

detailed central vision, appreciate detail

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48
Q

Centre of macula is called

A

fovea (slightly thinner than retina) so where there is a dip in the retina, this is fovea

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49
Q

How is eye divided

A

Anterior and posterior segment… divided by lens

50
Q

Boundaries of anterior chamber

A

Between Cornea and Lens

51
Q

What produces aqeous humor

A

Ciliary body EPITHELIUM

52
Q

Where does ciliary body sit compared to ciliary muscle

A

Medially

53
Q

What sits immediatey anterior to ciliary bodyand lens

A

iris

54
Q

Passage of aqeous himor

A

through lens zonules, arround lens into anterior chamber and then reabsorbed by trabecular meshwork

55
Q

Where does trabelcular meshowrk lie with respect to th eiris

A

Anterior to iris

56
Q

How is aqeous reabsorbed

A 
passive= uveal-scleral outflow 
Active= TM canal of schlemm (80%)
57
Q

Define glaucoma

A

Optic neuropathy with characteristic structural damage to the optic nerve, associated with:

  • progressive retinal ganglion cell death,
  • loss of nerve fibres and
  • visual field loss (starting from periphery to centre) and blindness
58
Q

Is glaucoma pressure in the eye?

A

No-it’s apoptosis of retinal ganglion cells

59
Q

What is optic disk look like in retinal cell death in glaucoma

A

Enlargement of Optic Disc Cupping

60
Q

What does pressure have to do with glaucoma

A

Sustained Raised Intraocular Pressure is risk factor

61
Q

Types of glaucoma

A

Primary (=open angle) –> TM dysfunction

Closed (acute or chronic) –> increased pressure pishing iris/lens complex forward blocking TM

62
Q

Risk factors of closed angle glaucoma

A

small eye (hypermetropia), narrow angle at trabecular meshwork

(treat w laser iridotomy to create a drainage hole on the iris)

63
Q

Which glaucoma could be symptomatic

A

Primary asymptomatic until late stages,
closed angle- sudden painful red eye,
and drop in vision.

64
Q

Differnetiate what an arteriole looks like vs venule on fundoscopy

A

venules more dilated

65
Q

Highly sensitive part of the retina

A

Fovea of Macula

66
Q

Why do things look brighter when in centre of your eye than out of periphery

A

only your fovea has the concentration of cones to perceive in detail.

67
Q

How are cenral and peripheral vision assessed

A

Central: Visual Acuity Assessment

periph: Visual Field Assessment

68
Q

What constitutes ‘central vision’ and where is this perceived on the retina

A

(Fovea has the highest concentration of cone photoreceptors)

Detail Day Vision, Colour Vision Reading, Facial Recognition

69
Q

What constitutes Peripheral vision and where i this perceived on the retinal

A

Movement, Night Vision

Navigation Vision

70
Q

Problems with navigating due to…

A

Peripheral vision loss

71
Q

Structure of retina: outline outer layer (i.e. furthest from the centre of the eye)

A

Outer Layer – Photoreceptors (1st Order Neuron) – Detection of Light

72
Q

Outline middle layer of retina and function

A

Middle Layer – Bipolar Cells (2nd Order Neurons) – Local Signal Processing to improve contrast sensitivity, regulate sensitivity

73
Q

Outline the inner layer of retina (this means closest to the centre of the eye)

A

Retinal Ganglion Cells (3rd Order Neurons) – Transmission of Signal from the Eye to the Brain

74
Q

t/f layer containing photoreceptors lays closest to the lens

A

F: it lies close to the choroid

75
Q

What is the macula lutea

A

=macula. (yellow patch), pigmented region at the centre of the retina of about 6 mm in diameter

76
Q

What forms the pit at the centre of the macula and why

A

Fovea- due to absence of the overlying ganglion cell layer

Fovea has the highest concentration of photoreceptors for fine vision

77
Q

Differentiate structure of rod and cone

A

Rod Photoreceptor has Longer outer segment with photo-sensitive pigment

78
Q

Differentiate functional property of rods and cones

A

Rod is more sensitive to light than cones (but cones faster)

DEEP IT!

79
Q

Which is responsible for:
scototopic
phototopic vision

A

scoto- night- rod

photo-day-cone

80
Q

More rods or cones

A

much more rods``

81
Q

Outline photoreceptor distribution

A

Rods: wide dist. all over retina, high density just outside macula (20-40 degrees from fovea) . Completely absent in the macula

Cones- high distrivution onyl in the macula

82
Q

T.F Rods have multiple peak light sensitivity and cones have just one

A

F- there are 3 cone photopigment subtypes:
S-blue
M-green
L-red

S for small waves (short wavelength is blue)
M for medium
and
L for large (long wavelength is red!)

only one rod (with peak sensitivity at 498nm, between cone S and M)

83
Q

What is Deuteranomaly

A

caused by the shifting of the M-cone sensitivity peak towards that of the L-cone curve,
causing red-green confusion.

84
Q

T/f colour vision deficit higher in males

A

true -8% males, 0.5% female

85
Q

What is Anomalous Trichromatism (i.e. deuteranomaly)

A

Colour Vision Deficiencies due to shifting of photo-pigment peak sensitivity

86
Q

What are dichromatism and monochromatism

A

In Dichromatism, only two cone photo-pigment sub-types are present.

In Monochromatism, there is complete absence of colour vision.

87
Q

Differentiate blue and red cone monochromatism

A

blue- normal day light visual acuity

red- no functional day vision

88
Q

What is ishihara test and what deficiency can they test for

A

Colour Perception Test

Ishihara Isochromatic Plates can test for red-green deficiencies only

89
Q

Outline process of dark adaptation

A

BIPHASIC- Increase in light sensitivity in
dark

Biphasic Process
• Cone adaptation 7 minutes
• Rod adaptation 30 minutes – regeneration of rhodopsin

The threshold intensity reduces so less stimulus required to activate these photoreceptors???

Cones adapt first (7 minutes), then rods overtake cones at the rod-cone break

90
Q

How long does it take for rods to reach maximum dark adaption, and what is regenerated

A

30 mins (it is extremely sensitive to light, and is photobleached when exposed to light, then regenerates when dark to allow some vision in dark)

91
Q

How long does light adaptation take

A

5 mins

92
Q

Mechanism of light adaptation

A

suppression of light sensitivity:

photo-pigment bleaching by bright light,
and neuro-adaptation inhibiting rod and cone function

+

The pupil also provides a minor degree of light and dark adaptation,
by acting as an adjustable aperture,
regulating the amount of light into the eye.

93
Q

What happens to rod function in light adaptation

A

Suppressed, and cone function takes over within one minute.

94
Q

Principle of refraction

A
  1. As light goes from one medium to another, the velocity CHANGES!
  2. As light goes from one medium to another, the path CHANGES!
95
Q

What is the index of refraction

A

speed of light in vacuum/speed of light in medium

denominator will always be smaller, as light travels fastest in vacuum, so IR always bigger or equal to 1

96
Q

T/f: angle of incidence=angle of refraction

A

f… Angle of incidence = Angle of Reflection
….

angle of incidence can be bigger or smaller than angle of refracrtion depending on direction of the light

97
Q

What does a converging and diverging lens do

A

converging: takes light rays and bring them to a point

diverging|: takes light rays and spreads them outward.

98
Q

What shape is a converging and divergin lens

A

converging- convexed

diverging- concave

99
Q

What is emmetropia

A

Adequate correlation between axial length (=length of eyeball) and refractive power

Parallel light rays fall on the retina (no accommodation)

100
Q

What is ametropia

A

Mismatch between axial length and refractive power

Parallel light rays don’t fall on the retina (no accommodation)

101
Q

4 types of ametropia

A

Nearsightedness (Myopia)
Farsightedness (Hyperopia)
Astigmatism
Presbyopia

102
Q

What is myopia

A

NEAR sightness.
Can see near. Can’t see far.
Parallel rays converge at a focal point anterior to the retina

103
Q

2 causes of myopia

A

excessive long globe (axial myopia) : more common

excessive refractive power (refractive myopia)

104
Q

Symptoms of myopia

A

Blurred distance vision
Squint in an attempt to improve uncorrected visual acuity when gazing into the distance
Headache

105
Q

What type of lens do you correct myopia with

A

you want the rays to converge furhter away (as they’re converging anterior to retina in this condition) so you give a diverging (i.e. concave) lens for correction

106
Q

What is hyperopia

A

Long sightedness
Can see far, not near
Parallel rays converge at a focal point posterior to the retina

107
Q

Causes of hyperopia

A

excessive short globe (axial hyperopia) : more common

insufficient refractive power (refractive hyperopia)

108
Q

Symptoms of hyperopia

A
  • visual acuity at near tends to blur relatively early
  • asthenopic symptoms : eyepain, headache in frontal region, burning sensation in the eyes, blepharoconjunctivitis
  • Amblyopia – uncorrected hyperopia > 5D
109
Q

What is visual acuity

A

clarity of vision

110
Q

What type of lens do you correct hyperopia with

A

Rays convering too far back, so you want a converging lens (to make rays converge sooner), so a convex lens

111
Q

Define astigmatism

A

Parallel rays come to focus in 2 focal lines rather than a single focal point

112
Q

Cause of 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)

113
Q

Symptoms of astigmatism

A

asthenopic symptoms ( headache , eyepain)
blurred vision
distortion of vision
head tilting and turning

114
Q

Treatment of astigmatism

A

regular: cylinder lenses with or without spherical lenses(convex or concave), Sx
irregular: rigid CL , surgery

115
Q

What is the near response triad

A

Pupillary miosis (sphincter pupillae constricts) to increase depth of field

Convergence (medial recti from both eyes) to align both eyes towards a near object- i,e. adduct medially

Accommodation (Circular Ciliary Muscle) to increase the refractive power of lens for near vision

116
Q

What is prebyopia

A

Naturally occurring loss of accommodation (focus for near objects)
Onset from age 40 years
Distant vision intact
Corrected by reading glasses (convex lenses) to increase refractive power of the eye

lens loses elasticity

117
Q

Treatment of presbyopia

A 
convex lenses in near vision
Reading glasses
Bifocal glasses
Trifocal glasses
Progressive power glasses
118
Q

4 types of optical correction

A
  1. Spectacle lens (monofocal or multifocal)
    2, Contact lenses (higher quality of optical image and less influence on the size of retinal image than spectacle lenses
    )
  2. Intraocular lenses (cataract crystalline lens)
  3. Surgical correction Keratorefractive surgery or
    Intraocular surgery : clear lens extraction (with or without IOL), phakic IOL
119
Q

What is clear lens extraction + IOL

A

like removing opaque lens in cataracts, except lens is clear (just not bending light well), so means takoing out clear lens and putting in IOL (intraocular lens)

120
Q

Problem with clear lens extraction woith IOL

A

Lose accommodation (patient will need reading glasses).

121
Q

Outline process of accommodattion

A

Contraction of the Circular Ciliary Muscle inside the Ciliary Body
This relaxes the zonules that are normally stretched between the ciliary body attachment and the lens capsule attachment
Note that zonules are passive elastic bands with no active contractile muscle
In the absence of zonular tension, the lens returns to its natural convex shape due to its innate elasticity
This increases the refractive power of the lens

122
Q

What is accommodation controlled by

A

CN3

Neuro (16 decks)

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