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Neural Biology 1 > outer coat > Flashcards

outer coat Flashcards

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1
Q

What is the outer coat of the eye formed by?

A
  • sclera

- as the eye is very delicate need a tough outer coat

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2
Q

What does the outer coat consist of ?

A
  • very thin
  • made of rigid, collagenous matrix
  • Outer coat constitutes the cornea and the sclera
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3
Q

Why does the outer coat of the eye need be tough ?

A

as the eye contains IOP (pressure which is pushing out)- so needs to resist the pressure within.
-Eye is constantly moving and is always under action of eye muscles - so needs to be tough outer coat
Protects the delicate internal ocular tissues

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4
Q

How is the cornea shape?

A

slightly oval

-longer in the horizontal dimension than the vertical

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5
Q

How much of the cornea is in the outer coat ?

A

(7%- of the total surface area of the globe)

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6
Q

How much of the sclera is in the outer coat?

A

(93%)

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7
Q

What can we measure of the structure ?

A
  • thickness

- curvature

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8
Q

What is the instrument to measure the , curvature of the cornea?

A

Keratometer

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9
Q

What would the radius of curvature be for the front part of the eye?

A

radius of curvature of the front part of the eye - 7.8mm- in the centre and flatten towards periphery- more elliptical in shape- more spherical in middle.

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10
Q

What would the radius of curvature be of the posterior part of the eye?

A

11.5mm

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11
Q

What happens prior to cataract surgery ?

A

Has 2 measurements :

  • length of eyeball from front back
  • shape of front of the eye ball
  • which tells them the power of intraocular lens to go in.
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12
Q

What is the sclera?

A
  • Largest part of the fibrous coat of the globe
  • Thickest posteriorly (1mm), thinnest under tendons of rectus muscles (0.3mm)
  • comprises collagen and proteoglycans
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13
Q

What is foramina?

A

holes - which in the sclera allows for blood vessels and nerves to pass through

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14
Q

What are the number of foramina needed for in the sclera?

A
  • Optic nerve
  • Short posterior ciliary arteries and nerves
  • Long ciliary nerves
  • Vortex veins
  • Anterior ciliary arteries
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15
Q

What are the 3 layers of the sclera?

A

Episclera
Scleral stroma
Lamina fusca
- comprises collagen and proteoglycans

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16
Q

What is episclera ?

A
  • The uppermost layer
  • blood vessels are located here
  • made up of loose connective tissue outside the sclera
  • Connects the sclera to the conjunctiva
  • Lies under Tenon’s capsule
  • Highly vascular
  • Vessels larger and darker than vessels of the conjunctiva
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17
Q

What is the Scleral stroma?

A
  • bulk of sclera

- regular scleral collagen- which makes up the main substance of the slcera

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18
Q

What is the Lamina fusca?

A

-looser connective tissue which is pigmented

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19
Q

What is episcleritis?

A

inflammation of the superficial layer of the sclera

  • distinct area of inflammation within the episclera- blood vessels dilated
  • blood vessels in the conjunctiva
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20
Q

What happens during eye muscle surgery ?

A

in children- they have a squint
-want to straighten eye- make sure visual axis is parallel again
can do this by strengthen one muscle or weaken one eye muscle- this involves detaching one muscle and stiching it back in a different location

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21
Q

What is the tenons capsule ?

A
  • sheet of connective tissue
  • thin fibrous sheath that envelops the globe from the limbus to the margins of the optic nerve.
  • runs from optic nerve to sclera
  • Inferiorly Tenons capsule is thickened to form the suspensory ligament of Lockwood
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22
Q

What is the tenons capsule known as?

A

Fascia Bulbi,

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23
Q

What is the cornea?

A
  • it is transparent
  • it bends light
  • big dioptiric power
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24
Q

What is the corneas 2 important functions ?

A
  • Protection

- Major refractive surface (2/3 of the refractive power of the eye (refracts light)- principle refractive surface

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25
Q

What is the measurement of the central corneal thickness ?

A

0.53mm

520um

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26
Q

What is the measurement of the peripheral corneal thickness ?

A

0.67mm

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27
Q

What is the average corneal thickness in the centre in population ?

A

0.54mm

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28
Q

What is the radius of anterior central curvature of the cornea ?

A

7.8mm

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29
Q

What is the radius of the posterior central curvature of the cornea ?

A

6.5mm

30
Q

What is the 5 different layers the cornea can be resolved to ?

A
  • Epithelium- made up to 5-7 layers of cells
  • stroma- bulk of cornea
  • endothelium
  • bowmans layer
  • descements membrane
31
Q

What is the anterior limiting membrane of the cornea?

A

bowmans membrane

32
Q

What is the posterior limiting membrane ?

A

descements membrane

33
Q

What is the corneal epithelium ?

A
  • 10% of the cornea
  • Stratified squamous non-keratinized- which makes it vulnerable - as keratin is waterproof - so cornea needs to compensate.
  • 50 microns thick
  • 5-6 cell layers
34
Q

What are the 3 cell types in the corneal epithelium ?

A

-Squamous cells - 2-3layers
-Wing cells- 2-3 layers
Basal cells- 1 layer

35
Q

What are the Non-epithelial cells in the corneal epithelium?

A

include lymphocytes and Langerhans cells

36
Q

What are the squamous cells ?

A
  • 2-3 layers of cells
  • Extensive surface projections (microvilli and microplicae)
  • irregular appearance- due to microvilli -
37
Q

What is in the microvilli (layer) of the squamous cells?

A
  • Glycocalyx provides a hydrophilic surface and anchors the tear film- they emanate from the microvilli
  • Most superficial cells linked by tight junctions forming an effective permeability barrier
38
Q

What are the wing cells ?

A

2 layers of cells

Polygonal with inferior indentations

39
Q

What are the wing cells like inside?

A
  • they have adjacent cells which are linked by extensive interdigitations (interlocking) and abundant desmosomes (anchoring component of cell) (adaptation to resist damaging shear forces)
  • Sparse organelles
  • Numerous intermediate filaments in the cytoplasm
  • No presence of organelles as would scatter light- dont need mitochondria- dont need lots of ATP for energy.
40
Q

What are basal cells ?

A
  • Single layer of cells
  • Mitotic cells
  • Structurally similar to wing cells
41
Q

What can you use with a Electron microscope ?

A

scan surface of structures with high mag

42
Q

What are the basal cells like inside ?

A
  • they have adjacent cells linked by desmosomes
  • Attached to the underlying stroma via a complex anchoring system
  • Nerve terminals seen between basal cells
43
Q

What is the epithelial anchoring system?

A
  • series of filaments which are anchoring the epithelium to the underlying stroma-
  • need an equally strong anchoring system between the epithelia and underlying stroma- in order to keep the epithelia on the surface.
44
Q

What is the bowmans membrane?

A

anterior limting membrane

-homogenous thin membrane

45
Q

What would we see in the electron microscope of the bowmans layer?

A

see that it is made up of randomly orientated collagen fibre

46
Q

What is the bowmans layer composed of?

A

-It is composed of a randomly orientated array of fine collagen fibrils

47
Q

How thick is the bowmans layer?

A

-8-14 microns thick

48
Q

What is the function of the bowmans layer?

A

Function is unclear

Thought that it is not critical to corneal integrity- can take it away and still have a healthy cornea

49
Q

What is the stroma made up of?

A
  • 90% corneal thickness
  • 78% water 1% salts -21%biological macromolecules
  • VERY HYDRATED and collagenouns structure
50
Q

How thick is the stroma?

A

500 microns thick

51
Q

What is the stroma composed of?

A

Composed of collagen fibrils embedded in a matrix of proteoglycans- attract water (very hydrophilic molecules)
Synthesized by keratocytes

52
Q

How is the collagen fibrils arranged in the stroma?

A

-arranged in lamellae

53
Q

What is the role of fibroblast?

A

synthesise collagen and proteoglycans

54
Q

What is the keratocytes ?

A

found in tendons

  • same function as fibroblasts- but are in the eye
  • synthesise collagen and proteoglycans matrix which fulls the space between the collagen fibrils
55
Q

What do you see in the electron microscope of the stroma collagen fibres?

A
  • organised in distinct layers
  • looks like a series of stripes
  • regular collagen, fine fibrils /thin
  • Electron microscopy shows that the collagen fibrils are small (25-35nm) and regularly arranged (a pre-requisite for transparency)- the reason cornea is like that is the reason it is transparent.
56
Q

What are the collagen types?

A

Collagen types I and V predomominantly (fibril type) with lesser amounts of type VI and type XII (non-fibril)

57
Q

What is the collagen orientation ?

A

-Vertically
-Horizontally
-Collagen fibrils have a preferred orientation corresponding to the medial lateral and superior-inferior axes of the cornea
This preferrental arrangement tends to occur more posteriorly than anteriorly and increases towards the limbus
-Limbal collagen takes the form of an annulus- when get to limbus. (periphery) they then start to form an annulus (a circle)

58
Q

What is the difference in the cornea to the sclera?

A
  • cornea is clear
  • sclera is opaque
  • collagen fibrils is much less regular organised in the sclera and very variable in size and no distinct pattern
  • collagen fibrils are very small and spaced and regularly arranged in the cornea- giving its transparent appearance.
59
Q

What is decements membrane?

A

-Posterior limiting membrane

60
Q

What is the descements membrane that the bowmans layer isn’t?

A
  • it is a basement membrane of the corneal endothelium .
61
Q

How thick is the basement membrane/descements membrane?

A

3-4 microns thick at birth, increasing to 10-12 microns in the adult

62
Q

What does the anterior and posterior part of decements membrane represent?

A

The anterior 1/3 of Descemets membrane represents that part produced in foetal life
The posterior 2/3 is formed postnatally

63
Q

How can you tell the age of the cornea?

A

looking at the thickness of the decements membrane

64
Q

What is the structure of the decement membrane?

A
  • bottom endothelium
  • decements membrane middle
  • stroma at top
65
Q

How do collagen fibre position themsleebs?

A

sometimes 90degrees to one another layers

66
Q

What is the corneal endothelium ?

A
  • -Monolayer of squamous cells-single layer of cells- doesnt need to be more than 1 layer as it is not there for protection.
  • it has metabolic support for the cornea
  • needs a lot of energy for its function- as it is involved in maintaining corneal hydration
  • Adjacent cells are linked by tight junctions (barrier function)- needs a barrier
  • Large numbers of mitochondria reflects their high metabolic activity compared to epithelium with none.
  • These cells can not regenerate- existing. cells need to spread to fill gaps when we are losing the corneal endothelial cells.
67
Q

What does the corneal endothelium appear as under the electron microscope?

A

Under the electron microscope, the lateral borders of endothelial cells are markedly convoluted

68
Q

What can we see in a specular microscope in a corneal endothelium ?

A
  • In tangential section the endothelium appears as a mosaic of polygonal (typically hexagonal) cells
  • Limited capacity for mitosis to replace damaged cells
  • There is a progressive reduction in endothelial cell number with age
  • Variation in cell size (polymegathism) and shape (pleomorphism) occurs with age, trauma, and contact lens wear
69
Q

What does the corneal endothelial cell appear as when you are young compared to old in a specular microscope ?

A

comparing a endothelium in a 13 yr old and 76 yr old -much larger in a older person than younger

  • very regular hexagonal shape in a young person
  • but a change in older person
70
Q

What is the properties of the cornea?

A
  • The cornea is the most richly innervated surface tissue in the body
  • Predominantly sensory (trigeminal innervation)
  • Reflex and trophic function- in terms of supporting the epithelium - reflex- intiates protection and trophic is the function of the corneal nerves to protect and support the corneal epithelium.
71
Q

What enters the cornea radially?

A
  • Nerve fibre bundles
  • They branch repeatedly forming a rich sub-epithelial plexus
  • Individual axons penetrate Bowmans membrane and terminate in the epithelium

Neural Biology 1 (58 decks)

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