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Ophthalmology > Anatomy: Eyeball > Flashcards

Anatomy: Eyeball Flashcards

1
Q

How many layers does the eyeball have?

A

3

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2
Q

What is the outer layer or the eyeball comprised of?

A

Sclera (white part) which continues anteriorly as the cornea

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3
Q

Is the cornea transparent?

A

Yes

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4
Q

Describe the outer layer

A

Tough and fibrous

Provides attachment for extra ocular muscles

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5
Q

What does the middle layer comprise of?

A

Choroid - vascular layer
Ciliary body
Iris

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6
Q

What does the ciliary body connect?

A

The choroid with the iris

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7
Q

What is the inner layer comprised of?

A

Retina

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8
Q

What are the 2 chambers of the eyeball

A

Anterior chamber

Posterior chamber

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9
Q

The anterior chamber is the space between…

A

Cornea and iris

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10
Q

Posterior chamber is the space between…

A

Iris and ciliary body and the lens

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11
Q

What structure secretes the aqueous humour that fills the chambers of the eye?

A

Ciliary processes within the ciliary body

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12
Q

What is the outer layer of the eyeball continuous with?

A

Dura mater covering optic nerve

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13
Q

Describe the iris

A

A thin contractile diaphragm with a central aperture for transmitting light

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14
Q

The central aperture of the iris is also called…

A

The pupil

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15
Q

What two muscles control the size of the pupil?

A

Sphincter and dilator pupillae

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16
Q

Is the lens anterior or posterior to the iris?

A

Posterior

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17
Q

Is the lens biconcave or biconvex?

A

Biconvex

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18
Q

The lens is enclosed in a capsule and attached to the ciliary body by…

A

The suspensory ligaments

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19
Q

The cavity behind the lens is filled with what type of humour?

A

Vitreous

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20
Q

Describe the vitreous humour

A

A transparent jelly like substance that supports the lens and holds the retina in place

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21
Q

What route does the aqueous humour take?

A

Flows from posterior chamber, through pupil into the anterior chamber. Drains through the iridocorneal angle. Then via trabecular meshwork into the canal of Schlemm

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22
Q

What structures does the aqueous humour nourish?

A

Lens and cornea - they are avascular (need to be transparent to let light pass through)

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23
Q

What does the canal of Schlemm drain into?

A

Venous circulation

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24
Q

The retina consists of what 2 layers?

A 
Neural layer (photosensitive) 
Pigmented layer
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25
Q

Is the pigmented layer or photoreceptive layer closer to the choroid?

A

Pigmented layer

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26
Q

What is the role of the pigmented layer?

A

Contains melanin

Absorbs scattered light to help focus images

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27
Q

What does the photosensitive layer of the retina generate in response to light?

A

Action potentials

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28
Q

The photosensitive layer is made up of photoreceptors called…

A

Rods and cones

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29
Q

What are some characteristics of rod photoreceptors?

A

Responsible for vision in low intensity light
Do not discern colour
More abundant in peripheral retina

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30
Q

What are some characteristics of cone photoreceptors?

A

Responsible to high visual acuity and colour vision
Concentrated in the macula
The centre of the macula (fovea) is only cones

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31
Q

What is the macula?

A

Dark area lateral to the optic disc
Centre of vision
Centre of macula contains fovea = only rod cells

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32
Q

Where is the area of most acute vision?

A

Fovea centralis (depression in centre of macula)

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33
Q

What is the 3 main roles of the cornea?

A

Maintain transparency
Ocular protection - including corneal reflex
Refraction of incoming light (along with tear film)

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34
Q

What are the 5 layers of the cornea?

A 
Epithelium
Bowman’s membrane
Stroma 
Descemet’s membrane
Endothelium
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35
Q

What type of cells make up the epithelial layer or the cornea?

A

Non keratinised stratified squamous cells (approx 5-7 layers thick)

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36
Q

When epithelial cells of cornea are damaged, what happens?

A

Cells migrate from the basal layer to surface (increase in the mitotic activity)

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37
Q

Where are corneal stem cells located?

A

At the periphery of the cornea (limbus)

Central corneal wounds heal slower that more peripheral

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38
Q

In the cornea, below what level will result in corneal scarring if trauma occurs?

A

Below Bowman’s layer (only the epithelium is regenerated)

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39
Q

What layer forms the bulk of the cornea?

A

The stroma layer - connective tissue (regularly organised collagen fibres)

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40
Q

What does Descemet’s membrane act as in the cornea?

A

The basement membrane to the endothelium

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41
Q

What is the main role of the corneal endothelium?

A

Maintain hydration in order for cornea to stay transparent

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42
Q

What type of cells make up the endothelial layer of cornea?

A

Simple squamous - does not regenerate
Number of cells fall as get older - less than 800 cells/m2 leads to corneal oedema and poor vision
Cellular loss accelerated by trauma, surgery and exposure to UV radiation

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43
Q

What is responsible for maintaining an adequate pressure in the eye?

A

Aqueous humour

44
Q

Intra ocular pressure is a balance between…

A

Rate of production and drainage of aqueous humour

45
Q

The majority of aqueous humour drains via canal of Schlemm, but 10-20% drains via a different route. What is this?

A

Uveoscleral route

Passes into the root of the iris and or ciliary muscle before draining into the scleral vascular system

46
Q

How is intra ocular pressure measured?

A

Measuring the force needed to flatten the corneal surface using a tonometer - greater force needed, the higher the pressure

47
Q

What is the normal range for intra ocular pressure?

A

11-21mmHg

48
Q

Above what IOP is considered to be ocular hypertension?

A

Above 21

49
Q

Autonomic control of IOP is via adrenergic or cholinergic mechanisms?

A

Adrenergic

50
Q

What receptor stimulation reduces IOP by reducing aqueous production (and may increase uveoscleral outflow)?

A

Alpha 2 receptors

51
Q

What receptor stimulation increases IOP by increasing aqueous production?

A

Beta 2 receptors

52
Q

What is the role of the lens?

A

Refract light

The lens can vary the amount it refracts light by changing its shape = accommodation

53
Q

Is increased accommodation required for near or far objects?

A

Near - light rays are more divergent so require greater refraction to bring them into focus on retina

54
Q

Light refracts as it passes through a number of structures and ‘fluids’. What are they?

A

From air to liquid tear film
Through cornea
Through lens

55
Q

Where does most light refraction occur?

A

At air- cornea interface

56
Q

During accommodation reflex, what happens?

A 
Eyes converge - image brought into focus on same point of retina in both eyes
Pupils constrict 
Lens bicovex(fatter)
57
Q

To make the lens more biconvex, what happens?

A

Ciliary body muscle contracts and move inwards - release tension on suspensory ligaments

58
Q

As we age the lens becomes stiffer, so degree to which it can accommodate becomes less. What is this called?

A

Presbyopia - age related inability to focus near objects

Most notable from 40-45 onwards

59
Q

What type of lenses can be prescribed for presbyopia?

A

Convex lenses

60
Q

When measuring ocular pressure, there is a correction factor. What is it?

A

The corneal thickness

61
Q

Does having a high IOP equate to a diagnosis of glaucoma?

A

Not necessarily

62
Q

A high IOP is a risk factor for what?

A

Glaucoma

63
Q

Beta blockers can be used to reduce IOP. What are some examples of these?

A

Timolol, carteolol

Reduce aqueous production

64
Q

Alpha agonists can be used to reduce IOP. What are some examples?

A

Apraclonidine, brimonidine

Reduce production and small increase in drainage

65
Q

How do prostaglandin analogues work in terms of IOP?

A

Increase uveoscleral outflow

66
Q

How do carbonic anhydrase inhibitors work with regards to IOP?

A

Reduce production of aqueous

67
Q

How do parasympathomimetics work with regards to IOP?

A

Increase outflow of aqueous by ciliary muscle contraction opening trabecular meshwork

68
Q

What is another name for the suspensory ligaments?

A

Zonules

69
Q

Do we require increased accommodation for near or far tasks?

A

Near

70
Q

Describe the lens capsule

A

A thickened basement membrane that envelopes the lens.

Responsible for changing lens shape during accommodation

71
Q

Does the lens continue to grow throughout life?

A

Yes

Lens covered in epithelium - undergo mitosis and form lens fibres
Newest layers on surface and older progressively deeper, so outer lens soft, whereas centre is hard

72
Q

What is a cataract?

A

Any opacity (loss of transparency) of the lens

73
Q

What makes up the uveal tract?

A

Iris
Ciliary body
Choroid

74
Q

The iris attaches to ciliary body at the …angle

A

Iridocorneal angle

75
Q

What does the iris control?

A

Amount of light that enters the eye by varying the size of the aperture (pupil)

76
Q

In conditions of low light or sympathetic activation the pupil dilates. This is called..

A

Mydriasis

Contraction of dilator pupillae pulls the pupil outwards to enlarge pupil diameter

77
Q

In conditions of bright light the pupil constricts. This is called…

A

Miosis
Sphincter pupillae is responsible for constriction - stimulated by parasympathetic activation (fibres carried in inferior division of CN 3)

78
Q

Does the sympathetic or parasympathetic NS innervate the sphincter pupillae?

A

Parasympathetic

Pre and post ganglionic ACh (so antimuscarinics/ muscarinics will act here)

79
Q

The dilator pupillae is under sympathetic control. NA activates what receptor on the muscle?

A

Alpha 1 receptor

80
Q

Tropicamide is an antimuscarinic, what effect will it have on the pupil?

A

Mydriasis

81
Q

Phenylephine is a sympathomimetic . What effect will it have on the pupil?

A

Mydriasis

82
Q

Pilocarpine is a muscarinic antagonist. What effect will it have on the pupil?

A

Miosis

83
Q

With age does miosis or mydriasis occur to pupil?

A

Miosis - dilator pupillae becomes atrophic and sphincter more fibrotic

84
Q

What are the primary roles of the ciliary body?

A

Accommodation
Aqueous humour production
Attachment for lens suspensory ligaments

85
Q

When the ciliary muscle contracts, what happens to the lens?

A

When muscle contracts it moves inwards, so less tension on suspensory ligaments and increasing the power of accommodation (lens more spherical)

86
Q

The choroid extends from the ciliary body to the…

A

Optic nerve

87
Q

What is the function of the choroid?

A

Allows nerves and vessels to reach anterior eye by passing through it
Removes waste products from outer retina
Supplies nutrients to outer half retina
Absorbs any light passing through retina

88
Q

What is the name of the basement membrane that attaches choroid to retina?

A

Bruch’s membrane

89
Q

What supplies the outer half of the retina?

A

Rich capillary bed in the choroid - choriocapillaris

90
Q

The vitreous cavity fills what fraction of the volume of the eye?

A

2/3

91
Q

What is the vitreous attached to?

A

Posterior lens capsule and retina

92
Q

What percentage of the vitreous is water?

A

99%

And it is 3x more viscous than water

93
Q

During what surgery can the anterior vitreous membrane be disrupted?

A

Cataract surgery (posterior lens capsule disruption -> anterior membrane of vitreous disruption)

94
Q

Describe vitreous detachment

A

With age fluid fills between potential space between retina and vitreous - detachment where it is weakly bound

95
Q

What can a vitreous detachment predispose to?

A

Retinal detachment

96
Q

What are the two layers of the retina?

A

The inner neural layer and the outer retinal pigment epithelium (RPE)

97
Q

What is the potential space called between the neural layer and RPE?

A

Subretinal space

98
Q

When does the neural layer and RPE fuse?

A

Early foetal life

99
Q

The inner 2/3 of the retina is supplied by what?

A

Central retinal artery

100
Q

How many branches does the central retinal artery divide into?

A

4 and each supplies a segment of the retina
Superior nasal and superior temporal
Inferior nasal and inferior temporal

They are end arteries

101
Q

Retinal arteries overly…

A

Retina veins

In certain situations e.g HTN characteristic changes can be seen where the vessels cross

102
Q

Which branches of the central retinal artery arch over the posterior pole?

A

Superior and inferior temporal retinal arteries

103
Q

Does the macula have a dense capillary network?

A

Yes BUT the fovea is absent from capillaries - dependent on underlying choriocapillaris

104
Q

What is the posterior pole?

A

Usually refers to the retina between the optic disc and the macula

105
Q

Is the macula located temporal or nasal to the optic disc?

A

Temporal

And bounded by the temporal superior and inferior vascular arcades

106
Q

The macula accounts for what percentage of the visual field?

A

Almost 10%

Ophthalmology (25 decks)

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