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C1 Modules > Embryology and anatomy of orbit > Flashcards

Embryology and anatomy of orbit Flashcards

1
Q

What are the characteristics of Early development?

A
  1. Neural tube precursor to CNS
  2. Neural groove deepens
  3. Day 17 - eye develops from cell population in anterior neural plate - eye fields
  4. Rapid growth of prosencephalon, forebrain
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2
Q

How is optic sulcus formed ?

A

week 4 - lateral shallow grooves
Cells of cephalic neural crest migrate - head mesoderm
Neural tube closure
Grooves from outpouchings - optic vesicle

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3
Q

What are optic vesicles?

A

Outgrowings of brain which make contact with surface ectoderm and this contact induces changes necessary for further development of eye

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4
Q

What is the optic disc?

A

White, cup-like area in centre of optic disc

vesicles contact surface ectoderm - important for lens formation

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5
Q

What happens on day 22?

A

Two small grooves develop on either side of developing forebrain in neural folds –> optic sulci

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6
Q

What happens in the optic cup?

A

Vesicles contact surface ectoderm - important for lens formation

Invagination of optic vesicle - double walled optic cup

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7
Q

What develops after invagination of the inferior optic cup?

A

Choroid fissure for hyaloid artery

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8
Q

What is optic vesicle?

A

As neural tube closes, groove become outpockings

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9
Q

Where do optic vesicle extend from?

A

Forebrain toward surface ectoderm through adjacent mesenchyme

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10
Q

What happens as the optic vesicles grow toward ectoderm?

A

Their connection to the forebrain become attenuated to form optic stalks

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11
Q

What is the development of optic cup?

A
  1. The portion of each optic vesicle interacts with surface ectoderm induces that area of ectoderm to form a thickening called lens placode
  2. The lens placode invaginate to become a lens pit, soon forms a complete circle that pinches off from surface ectoderm to become a lens vesicle
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12
Q

What is lens placode?

A

A precursor of lens

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13
Q

What has optic or choroidal fissure?

A

The developping optic vesicle and stalk have a groove on their inner surface

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14
Q

What is the function of choroidal fissure?

A

Blood vessels gain access to optic cup as well as lens vesicle

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15
Q

What are branches of hyaloid artery?

A

A branch of the opthalmic artery and its accompanying vein

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16
Q

What will the choroid fissure do?

A

Fuse

Completing eye wall inferiorly and enclosing vessels in a canal in optic stalk

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17
Q

What happens during 5th week of optic cup development ?

A

Vesicle lose contact with ectoderm lying in the mouth of optic cup

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18
Q

Lens vesicle

A
  1. surface ectoderm - lens placode
  2. Placode invaginates - lens vesicle
  3. 5th week vesicle loses contact with ectoderm lying in mouth of optic cup
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19
Q

What do the cells of the posterior part of lens vesicle transform into?

A

Elongated, slender primary lens fibre

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20
Q

What are the posterior cells for lens development?

A

Parallel fibres forming lens nucleus

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21
Q

Lens development

A

Posterior cells
Crystalline proteins deposited intracellularly - refractive properties
Anterior layer forms cuboidal lens epithelium - regulated by fibroblast growth factors

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22
Q

Optic stalk development

A
  1. Optic cup connected to the diencephalon - optic stalk
  2. Transient space - optic ventricle connects to 3rd ventricle via stalk
  3. Inferiorly have continuation of choroid fissure - fuses at 7-8 weeks
  4. Narrow tunnel in optic stalk
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23
Q

What does hyaloid artery become?

A

Central retinal artery

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24
Q

How are optic nerve fibres developed?

A
  1. In the framework of optic stalk
  2. Fibres from nerve fibre layer of retina grows into optic stalk by passing through choroidal fissure
  3. Inner and outer layers fuse, inner layer providing supporting neuroglial cells
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25
Q

What develops into glial system of nerve?

A

The neuroectodermal cells forming the walls of optic stalk

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26
Q

How are the fibrous septa of optic nerve developed?

A

Vascular layer of mesenchyme which invades nerve at 3rd fetal month

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27
Q

Inner wall of stalk

A

Nerve fibres from retina

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28
Q

What will the two layers of optic cup further differentiate into?

A

Retina of mature eye

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29
Q

Two layers are unequal in size

A

The outer one is thinner than inner one

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30
Q

What are the 2 portions that the optic cup be divided into?

A
  1. Anterior 1/5 (rim)

2. Posterior 4/5 (rim)

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31
Q

What will the rim area in the retina form?

A

Iris and ciliary body

The posterior 4/5 will form retina

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32
Q

What will the outer layer of posterior 4/5 become?

A

Layer of retina

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33
Q

What will the inner layer become?

A

Neural retina

Separated by intraretinal space

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34
Q

What will the posterior 4/5 of inner layer differentiate into?

A
  1. Photoreceptive rods and cones (pars optica retina)
  2. Ganglion cells
  3. Bipolar nerve cells
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35
Q

what gives rise to epithelium of iris and ciliary body?

A

Anterior rim of optic cup

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36
Q

What contributes to pigmented epithelial layer?

A

Outer layer of optic cup

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37
Q

What is the role of ciliary body?

A
  1. Accomodation
  2. Aqueous humour production
  3. lens maintenance
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38
Q

What do stroma of iris and ciliary body develop from?

A

Neural crest cells that migrate into area

39
Q

What develops from optic cup neuroectoderm?

A

Within stroma of iris

Sphincter pupillae and dilator pupillae

40
Q

What is the function of iris and ciliary body?

A

Controls light level via central aperture-pupil

41
Q

What are Iris and Ciliary body?

A

Optic cup margins

42
Q

What is RPE?

A

External pigment layer of iris

43
Q

What is the inner layer of iris and part of ciliary body?

A

Anterior 1/5 inner layer of optic cup

44
Q

What are sphincter and dilator pupillae muscles?

A

Neural ectoderm in vascular mesenchyme surrounding iris

45
Q

What are the suspensory ligaments of lens?

A

Loose mesenchyme between lens and ciliary body

46
Q

What does ciliary process fold secrete?

A

Aqueous humour

47
Q

Where does the vitreous body form?

A

Centre of optic cup posterior to the lens

48
Q

Where are the vitreous humor derived from?

A

Mesenchymal cells of neural crest origin

49
Q

What does vitreous humor contain?

A

Phagocytic cells

Remove blood and other debris

50
Q

What does the mesenchyme *(mesoderm) invade?

A

Optic cup - choroid fissure

51
Q

What happens during end of embryonic period, week 8?

A

Optic cup and lens are supplied by hyaloid artery

52
Q

What are hyaloid vessels?

A

Vascular layer on inner surface of retina and delicate fibre network between lens and retina

53
Q

What is vitreous body?

A

interstitial network spaces filled with transparent gelatinous
substance

54
Q

vitreous blood supply–

A

from mesenchyme surrounding
pigment epithelium of optic cup to form richly vascularised
pigment containing choroid

55
Q

What does the outer layer of mesenchyme form?

A

Outer tough collagen rich sclera

56
Q

What does the sclera correspond to?

A

Dura mater of brain and is continuous with dura of optic nerve

57
Q

Where are extrinsic ocular muscles derived from?

A

Pre-otic myotomes

58
Q

What are the 2 layers that the external surface of optic cup condenses into?

A
  1. Inner, pigmented, vascular layer = choroid

2. Outer, fibrous layer = sclera

59
Q

What is cornea?

A
  1. Anteriorly to sclera

2. Continuous with corneal stroma

60
Q

What are the 3 layers of cornea?

A
  1. External epithelial lauer (surface ectoderm)
  2. Middle dense connective tissue (Substantia propria) - continuous with sclera
  3. Inner flat epithelium - from mesenchyme, lining anterior chamber space
61
Q

How are cornea richly vascularised?

A

loose connective tissue between anterior
chamber and lens - continuation of choroid- irido-pupillary
membrane
involutes, leaving pupil unobstructed

62
Q

What are eyelids?

A

folds of ectoderm and associated

mesoderm

63
Q

What happens to the eyelid at end of embryonic period?

A

Still open

64
Q

What are the undersides of eyelids lined by?

A

delicate ectodermal
epithelium with loose richly vascularised
connective tissue, continuing onto sclera as
conjunctiva

65
Q

What are the master gene for eye development?

A

PAX6

66
Q

Where is PAX6 initially expressed?

A

band in anterior neural ridge

of neural plate before neuralation

67
Q

PAX6 master gene

A

initially single eye field which separates into 2

primordia

68
Q

What is separation signal for molecular regulation?

A

Sonic-hedgehog expression expressed in prechordal plate

69
Q

What is role of SHH?

A

up-regulates PAX2 expression in optic stalks
and down-regulates PAX6, restricting expression
to optic cup and lens

70
Q

Globe and soft tissue

A 
adult globe axial diameter
25mm
 cornea & sclera medium to
low signal on T1 &T2
 ciliary body, iris &
choroido-retinal layer T1
hyperintense
 aqueous humour T1
hypointense & T2
hyperintense
 posterior chamber
vitreous- 98% water, <2%
collagen
 lens - 65% water, 35%
protein; intermediate T1
signal &amp; T2 hypointense;
hyperdense on CT
71
Q

What are the optic nerve?

A

white matter tract surrounded by pia, arachnoid

and dura

72
Q

Optic nerve

A

subarachnoid space (0.5-0.6mm) continuous
with intracranial CSF, and widest behind globe
 sheath dura blends with sclera anteriorly and
periorbita of optic canal posteriorly
 continuous with intracranial dura
 intracanalicular segment, 5mm long; passes
above ophthalmic artery in optic canal and then
through annulus tendon of Zinn

73
Q

How many muscles control movement of eye?

A

6

74
Q

How many muscles control eyelid elevation?

A

1

75
Q

What are extra-ocular muscles 1?

A
  1. 4 recti
  2. 2 oblique
  3. Levator palpebrae superioris (striated)
76
Q

Where does recti originate from?

A

tendinous annulus of Zinn -

orbital apex

77
Q

Medial rectus largest

A

inferomedial annulus &

optic nerve sheath

78
Q

smaller lateral rectus

A
  • common tendon above &

below SOF

79
Q

Inferior rectus

A

Below orifice of optic canal

80
Q

Superior rectus

A

Annulus above optic nerve and dural sheath

81
Q

Levator palpebrae superioris

A

from lesser

sphenoid wing & superior rectus fibrous origin

82
Q

superior oblique

A

e longest & thinnest muscle
courses anteromedially; tendon reflects around
fibrocartilaginous trochlea then posteromedially
at 45° degrees inferior to superior rectus

83
Q

inferior oblique

A

from orbital plate of maxilla

lateral to opening of nasolacrimal canal

84
Q

Osseous anatomy 1

A

orbit pyramidal cavity; complex bony anatomy
 medial & lateral walls vertical
 roof convex upwards but horizontal
 floor slopes downwards-medial to lateral

85
Q

Medial orbital wall

A 
 frontal process of maxilla
 lacrimal bone with anterior
&amp; posterior lacrimal crests
 orbital plate of maxilla with
ethmoid &amp; frontal bone
above
 major component – lamina
papyracea
 sphenoid at apex
86
Q

Orbital floor

A 
 triangular shape
 orbital plate of maxilla
medially
 zygomatic bone laterally
 palatine bone near apex
 separated by inferior
orbital fissure from lateral
wall (CN5-V2, IOV)
 grooved by infra-orbital
foramen and canal
87
Q

Lateral orbital wall

A 
mainly zygomatic bone
with anterior condensation
forming lower half
 frontal bone above frontozygomatic suture
 greater wing sphenoid- lies
postero-superior to inferior
orbital fissure, &amp; separated
by superior orbital fissure
from lesser wing sphenoid
and optic canal (CN3,4,6 ,
V1 &amp; SOV)
88
Q

Roof and optic canal

A 
majority of roof-orbital plate
of frontal bone
 lesser wing sphenoid -small
posteromedial component
 optic canal- wall of ethmoid
and sphenoid sinuses
medially, lesser sphenoid wing
cranially, anterior clinoid
process laterally &amp; optic strut
caudally
 strut of bone separates it
from superior orbital fissure
 mean diameter- 5mm; roof
length10-12mm
89
Q

Arteries 1

A

 dual supply-ophthalmic artery & ECA branches
 OA from ICA; below optic nerve - enters optic
canal within the dural sheath
 pierces dura near orbital apex, lies lateral to the
nerve giving rise to central retinal artery
 after genu crosses over nerve lying below
superior rectus and running anteromedially
alongside superior oblique and medial rectus
 central retinal artery -inferior to optic nerve,
entering dural sheath 1cm posterior to globe

90
Q

Arteries 2

A

other OA branches -long & short posterior ciliary,
muscular, lacrimal, anterior & posterior ethmoid,
supra-orbital & palpebral arteries
 transosseous branches to lateral orbital wall -
small branches of superior temporal / anterior
temporal branch of ECA
 anastamoses around orbital floor between
muscular branches of OA,anterior deep temporal
and infra-orbital artery, a branch of internal
maxillary
 lids have rich blood supply from both OA,
transverse facial, zygomaticomalar, facial &
infraorbital branches

91
Q

Veins

A

major vein - superior ophthalmic vein, to
cavernous sinus via SOF
 anastamosis of angular and nasofrontal veins
 runs anteromedially to posterolaterally over optic
nerve
 inferior ophthalmic vein runs posteriorly in
relation to inferior rectus and either drains to
SOV or cavernous sinus
 remaining orbital veins small and variable
 vortex veins –anastamosing veins between SOV
and IOV

92
Q

Congenital abnormalities

A 
Trisomy 13,18,21
 Cat-eye syndrome (chr 22) –
vertical orientated iris coloboma
 Congenital retinoblastoma – AD
 Congenital cataracts, glaucoma
 Persistent
hyaloid artery, pupillary
membrane, hyperplastic vitreous
93
Q

Maternal Infection

A 
 Viral- rubella, herpes simplex,
cytomegalovirus
cataracts, microphthalmos, necrosis
 Toxoplasmosis
inflammation &amp;/or retinal
detachment
 Syphilis
chorioretinal atrophy
94
Q

Maternal Teratogens

A 
Alcohol
FAS abnormalities of face/eye
 Hydantoinmicrophthalmos, colobomas
 LSD
severe eye abnormalities
 Thalidomide
absence of eye

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