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Module 8 > Structure of Eyeball > Flashcards

Structure of Eyeball Flashcards

1
Q

what are the components of the eye

A
  1. eyeball
  2. adnexa (ocular muscles, eyelids, lacrimal apparatus)
  3. housed in orbit (bony margins, copious fat)
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2
Q

what are the orientation of the eyeball

A
  1. poles
  2. optic axis
  3. equator
  4. meridian
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3
Q

name the structures

A
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4
Q

what are the 3 tunics of the eyeball

A
  1. external fibrous tunic
  2. middle vascular tunic
  3. internal nervous tunic
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5
Q

what is the function of the external fibrous tunic

A

gives shape to eyeball

protective

complete

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6
Q

what are the functions of the middle vascular tunic

A

blood vessels

smooth muscle

nutrient supply

control lens and pupil shape and size

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7
Q

what is the function of the internal nervous tunic

A

translation of visual signal into nerve impulses and transmission to brain

functional –> where light is converted into nervous signals

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8
Q

what is the fibrous tunic made up of

A

dense, collagenous

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9
Q

what are the functions of the fibrous tunic

A

resist internal pressure of material in chambers

gives shape to eyeball

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10
Q

what are the two parts of the fibrous tunic

A
  1. cornea
  2. sclera

meet at limbus

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11
Q

what is the cornea made up of

A

connective tissue –> lamellar/layered arrangement

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12
Q

what is the main part of the cornea

A

substantia propria

anterior and posterior lining epithelium

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13
Q

where are is the anterior epithelium

A

continuous with conjunctival epithelium –> contains sensitive nerves

responsible for corneal reflex

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14
Q

what is the posterior epithelium

A

continuous with anterior surface of iris

supplies nutrients to cornea (no vessels)

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15
Q

what is the basement membrane of the cornea

A

descemet’s membrane

last barrier to penetration of cornea (ulceration)

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16
Q

what is the sclera made up of

A

opaque/white

collagenous and elastic fibres

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17
Q

what is the function of the sclera

A

entry points for nerves and vessels

attachments for ocular muscles anterior to equator

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18
Q

what is the thin membranous covering that separates the eyeball from retrobulbar fat and what does it allow

A

vagina bulbi

allows eyeball free movement in socket

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19
Q

what are the 3 parts of the vascular tunic

A
  1. choroid
  2. ciliary body
  3. iris
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20
Q

what is the choroid

A

lines sclera from optic nerve to limbus

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21
Q

what is the ciliary body

A

thickening of tunic area at level of limbus

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22
Q

what is the iris

A

projects into cavity behind cornea

easily visible

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23
Q

what are the functions of the vascular tunic

A
  1. vascular supply
  2. suspends lens and controls shape of lens and pupil
  3. vessels enter eyeball at posterior pole and around equator
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24
Q

name the structures

A
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25
Q

what vessels are contained in the choroid

A

blood vessels in pigmented connective tissue

posterior ciliary arteries and vorticose veins

supplies nervous tunic via layer of capillaries

vessels seen with opthalmoscope

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26
Q

where is the avascular layer in the choroid

A

dorsal avascular layer between capillaries and larger vessels

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27
Q

what is the tapetum lucidum

A

reflective area –> sends light back through retina –> increases sensitivity of eye to low light

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28
Q

what is the ciliary body

A

thickened ridged ring around lens

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29
Q

what are the ciliary processes

A

extend zonular fibres to lens –> suspends lens

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30
Q

where is the smooth ciliary muscle and what is the function

A

between ciliary body and sclera

alters lens shape and alters lens focusing

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31
Q

what is the iris and where does it attach to

A

flat ring of tissue

peripheral attachment to sclera and ciliary body

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32
Q

what is the central opening of the iris

A

pupil

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33
Q

what muscles control the dilation/constriction of pupil

A

smooth spincter (constrictor –> parasympathetic) and radial dilator (sympathetic) muscles control pupil size

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34
Q

what does the pupil divide

A

anterior and posterior chambers

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35
Q

what are iridic granules

A

projections from dorsal border across pupil

horse, ruminant

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36
Q

what is part of the nervous tunic

A

retina

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37
Q

what does the retina line

A

choroid from optic nerve to pupillary margin

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38
Q

what are the parts of the retina that can be reached by light and what does it contain

A

posterior 2/3

contains receptor cells (pars optica retinae)

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39
Q

what part of the retina is not reached by light

A

anterior 1/3

has no receptors (pars ceca retinae)

continues onto iris

40
Q

what is the pigmentation of the retina

A

black appearance of pupil –> absorbs light

41
Q

what is the junction between optic and blind parts of the retina

A

ora serrata

level of junction between ciliary body and choroid

42
Q

what is the optic disc

A

extension of brain arising from optic nerve

43
Q

what are the retinal layers of the nervous tunic

A
  1. choroid
  2. pigmented epithelium
  3. neuroepithelial cells
  4. bipolar ganglion cells
  5. multipolar ganglion cells
44
Q

what are the layers of the retina

A
45
Q

where is the pigmented epithelium absent

A

no pigment over tapetum

46
Q

what are the neuroepithelial cells

A

receptor cells

  1. rods –> B/W & night vision
  2. cones –> colour & day vision
47
Q

what are the multipolar ganglion cells

A

axons pass to optic disc and form optic nerve

48
Q

what inserts at the optic nerve

A

entry of optic nerve (CN II)

no receptor cells –> blind spot

easily seen with opthalmoscope

49
Q

what is the area of the dorsolateral to optic disc

A

optimal resolution

macula

50
Q

what is the visual axis

A

macula-centre of lens-object viewed

51
Q

what is the refractive media

A

focussing of light through structure of eyeball

52
Q

what are the components of the refractive media

A
  1. cornea –> major role in refraction of light
  2. aqueous humor –> anterior and posterior chambers
  3. lens
  4. virteous body –> virteous chamber
53
Q

what is the aqueous humor and its function

A

clear, watery

maintains ocular pressure

54
Q

what produces the aqueous humor

A

ciliary process cells –> enter posterior chamber

55
Q

how does the aqueous humor enter and exit

A

anterior chamber via pupil

exits via iridocorneal (drainage)/angle (venous sinuses in sclera)

56
Q

how is the aqueous humor drained and produced

A

drainage = production

constant intracular pressure

57
Q

what does failure to drain aqueous humor cause

A

glaucoma

58
Q

what is the lens

A

elastic

regularly arranged fibres –> transparency

outer capsule –> attachment of zonular fibres around equator (thickest part of capsule)

59
Q

what is lens accomodation

A

lens will be thick if no external force –> circular ciliary muscle relaxed = wide circle )thin lens)

  1. muscle contracts –> relaxes zonular fibres (thick lens) –> close vision
  2. muscle relaxes –> tightens zonular fibres (thin lens) –> far vision
60
Q

what is the process here (fibres involved, shape of lens)

A
61
Q

what is the vitreous body

A

gel-like mass

high water content = vitreous humor

thin surface membrane

62
Q

what is the function of the vitreous body

A

maintains contact between retina and choroid

hyaline artery passes to lens in embryo –> regresses after birth

63
Q

what is the volume of the vitreous body

A

constant

not reduced/drained –> won’t cause pressure buildup

64
Q

how can the eye be imaged

A
  1. opthalmoscope –> direct
  2. ultrasound (cheap, simple, allows assessment of retina)
  3. CT and MRI may be useful but more for orbital disease
65
Q

what is the function of the adnexa

A

protect and move eye

66
Q

what are the components of the adnexa

A
  1. orbit
  2. orbital fasciae
  3. ocular muscles
  4. eyelids
  5. conjunctiva
  6. lacrimal apparatus
67
Q

what is the orbit

A

“conical” cavity on the lateral side of skull

68
Q

what bones are in the orbit

A

frontal, lacrimal and zygomatic bones

69
Q

which species have orbital ligament

A

carnivores and pig

70
Q

what is in the orbit in horse and ruminants

A

zygomatic process

71
Q

what are the openings of the orbit

A
  1. optic canal
  2. orbital fissure
  3. ethmoidal foraminae
  4. lacrimal sac fossa (leads to nasolacrimal duct)
72
Q

what is the orbit lined with

A

fibrous sheets (periorbita) and fatty connective tissue –> allows free movement of eyeball

73
Q

what are the structures of the orbit

A
74
Q

what are the 4 rectus muscles

A
  1. dorsal
  2. ventral
  3. medial
  4. lateral
75
Q

what are the 2 oblique muscles

A
  1. dorsal
  2. ventral
76
Q

where do the ocular muscles originate from

A

optic canal area

77
Q

what are the functions of oblique muscles

A

maintain orientation of visual axis

78
Q

what are the functions of the ocular muscles

A

sheets of smooth muscle maintain eyeball protrusion and eyelid opening

79
Q

what are the true eyelids called

A

palpebrae

80
Q

what are the true eyelids

A

musculofibrous folds

upper and lower lids

meet at angles of eye (commissures)

81
Q

what are the 3 layers of eyelids and conjunctiva

A
  1. skin
  2. musculofibrous
  3. mucous membrane = palpebral conjunctiva
82
Q

what are these structures

A
83
Q

what are the layers of the eyelids

A
  1. musculofibrous layer
  2. tarsus - fibrous plate
84
Q

what is the musculofibrous layer

A

orbicularis oculi

orbital septum

levator palpebrae superioris

smooth muscles

85
Q

what is the tarsus - fibrous plate

A

stabilizes edge of eyelid and gives shape to palpebral fissure

tarsal (meibomian) glands and cilia (eyelishes) along margin (secrete part of tear film)

86
Q

what are the structures of the eyelids

A
87
Q

what are the components of the conjunctiva

A
  1. palpebral conjunctiva –> lines lids
  2. bulbar conjunctiva –> reflects over sclera, epithelium anterior to cornea
88
Q

what is the conjunctival sac

A

the space between lids and eyeball (spot for foreign bodies)

89
Q

what is the 3rd eyelid

A

conjunctival fold –> central cartilage

conjunctiva on both sides –> not true eyelid

90
Q

how is the 3rd eyelid retracted

A

by smooth muscle

orbitalis

covers eyeball when retracted into orbit

91
Q

what is the function of the lacrimal apparatus

A

production of lacrimal fluid (tears) –> protection, corneal nutrition

92
Q

what are the glands in the lacrimal apparatus

A
  1. lacrimal –> dorsolateral wall or orbit
  2. gland of 3rd eyelid –> around base of 3rd eyelid cartilage, deeper gland in pigs and cattle (AKA nictitans/nictitating gland)
93
Q

which lacrimal gland causes cherry eye

A

inflammation of nictitans/nictitating gland

94
Q

what are the glands

A
95
Q

where is the drainage of tear film in the lacrimal apparatus

A

puncta lacrimalia

slits adjacent to caruncle

feed into lacrimal sac –> sacs drain into –> nasolacrimal duct –> runs through maxillan and drains into nasal cavity

96
Q

where does the tear film pool at

A

at medial angle of eye –> lacrimal lake

fluid repelled from edge of lids by fatty secretion of tarsal glands

97
Q

what are the 3 layers of the tear film

A
  1. outer: lipid, from tarsal glands (even spread of tears and integrity of film)
  2. middle: aqueous, from lacrimal glands (moisture, nourishment)
  3. inner: mucinous from goblet cells in conjunctiva (maintains film contact with cornea)

Module 8 (43 decks)

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