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ANATOMY2: Structure of the eye > Vitreous > Flashcards

Vitreous Flashcards

1
Q

What is the largest cavity of the eye?

A

the vitreous cavity

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2
Q

What proportion of the total volume of the eye is the vitreous cavity?

A

two thirds

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3
Q

What is the weight of the vitreous cavity?

A

3.9g

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4
Q

What is contained in the vitreous cavity?

A

vitreous humour or vitreous

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5
Q

What are the anterior and posterior boundaries of the vitreous cavity?

A
  • anterior: lens, posterior lens zonules and ciliary body
  • posterior: retinal cup
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6
Q

What is the vitreous?

A

transparent viscoelastic gel that i smore than 98% water with a refractive index of 1.33

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7
Q

What is the refractive index of the vitreous?

A

1.33

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8
Q

How does the viscosity of the vitreous compare to that of water?

A

it is 2-4x more viscous than water

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9
Q

What are the 6 main constituents of the vitreous?

A
  1. water
  2. hyaluronan (hyaluronic acid)
  3. collagens type II, VI, XI
  4. fibronectin
  5. fibrillin
  6. opticin
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10
Q

What are the 3 types of collagen within the vitreous?

A
  1. II
  2. VI
  3. XI
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11
Q

Which constituent of the vitreous is its gel structure dependent upon?

A

the collagenous constituents (not hyaluronan)

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12
Q

How are the collagen fibres arranged with the hyaluronan molecules in the vitreous gel?

A

the fine diameter type II collagen fibres (8-12 nm in diameter) entrap large coiled hyaluronan molecules

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13
Q

What is the overall shape of the vitreous?

A

shaped like a sphere with an anterior depression, the hyaloid fossa (also known as the patellar or lenticular fossa)

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14
Q

What are the two portions that the vitreous is traditionally regarded as consisting of?

A
  1. cortical zone
  2. central vitreous
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15
Q

How do the cortical zones and central vitreous differ microscopically?

A

cortical zone characterised by more densely arranged collagen fibrils

central vitreous is more liquid

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16
Q

How can the vitreous be further subdivided into major topographical zones, beyong the cortical zone and central vitreous?

A

3 zones:

  1. intermediate zone
  2. preretinal zone
  3. retrolental zone
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17
Q

What structures attach the cortical vitreous to points around its margin?

A

condensation of fine collagen fibrils

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18
Q

What are the 4 key points at which the cortical vitreous is attached to points around its margin?

A
  1. the peripheral retina and pars plana via the vitreous base, a 3-4mm wide band
  2. the posterior lens capsule (ligamentum hyaloide capsulare)
  3. the retina along the margins of the optic disc (base of the hyaloid canal)
  4. the inner limiting membrane of the retina, especially near retinal vessels
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19
Q

What is the name of the attachment of the vitreous to the posterior lens capsule?

A

ligamentum hyaloide capsulare

20
Q

What is another way of referring to the point where the vitreous attaches to the retina along the optic disc margins?

A

base of the hyaloid canal

21
Q

What attachment of the vitreous is disputed?

A

attachment to the retina along the margins of the optic dic (base of the hyaloid canal)

22
Q

What is the most variable and weakest of the vitreous attachments?

A

the attachment to the inner limiting membrane of the retina, especially near the retinal vessels

23
Q

What structure traverses the central vitreous?

A

central fluid-filled canal (hyaloid or Cloquet’s canal)

24
Q

What does Cloquet’s (hyaloid) canal represent?

A

the remants of the course taken by the hyaloid artery that supplied both the vitreous and lens during embryogenesis and early fetal life

25
Q

Which of the 3 major topographical zones of the vitreous are semi-liquid?

A

retrolental and intermediate zones

26
Q

Why is the existence of an ordered, orgnised, vitreal structure still controversial?

A

problems of studying a gel that is 98.5-99.% water

27
Q

At what age does the human vitreous begin to degenerate?

A

adolescence

28
Q

What structures appear in the human vitreous once it begins to degenerate?

A

liquid-filled cavities and fibrillar strands such as the retrolental, preretinal and other named tracts of significance only to vitreal specialists

29
Q

What are 5 major vitreous condensations that appear as the vitreous starts to degenerate in adolescence?

A
  1. rerolental tract
  2. preretinal tract
  3. vitreous base
  4. anterior hyaloid face
  5. vitreous cortex
30
Q

What is the nature of most of the central vitreous tracts and which 1 is the exception?

A

most are mobile and change during eye movements

exception: preretinal

31
Q

What may appear in the posterior vitreous cortex when the vitreous degenerates?

A

cortical holes, or pockets

32
Q

Where do the ‘cortical holes’ or pockets in the posterior vitreous cortex occur, if present?

A

occur close to the fovea, retinal vessels and any developmental anomalies

33
Q

What is the risk of cortical holes, or pockets, developing in the posterior vitreous cortex?

A

secondary pathological holes may develop following various disease processes

34
Q

What is the name of the thin potential space between the surfce fo the cortical vitreous and the retina?

A

subhyaloid or sublaminar space

35
Q

What may cause the subhyaloid (sublaminar) space between the cortical vitreous and retina to fill with fluid?

A

in cases of vitreous detachment

36
Q

In what region may the vitreous detach relatively easily?

A

in the posterior segment where it is less weakly bound to the retina

37
Q

In what scenario may fluid accumulate rapidly following vitreous detachment? When does it develop more slowly?

A

rhegmatogenous vitreous detachment

more slowly: where cortex is not ruptures (arrhegmatogenous vitreous detachment)

38
Q

What type of change is cortex rupture in rhegmatogenous vitreous detachment?

A

age-related change in the vitreous detachment

39
Q

What serious condition may vitreous detachment predispose to?

A

retinal detachment

40
Q

Are there cells in the vitreous?

A

is essentially acellular however occasional isolated cells may occur in the cortex, particularly near the vitreous base, optic disc and retinal vessels

41
Q

What are the three places in the vitreous cortex where isolated cells may occasionally occur?

A
  1. near vitreous base
  2. near optic disc
  3. near retinal vessels
42
Q

What is the main cell type in the vitreous?

A

hyalocytes

43
Q

What cells are hyalocytes, the main cell type in the vitreous, similar to and how?

A

macrophages: they have the same morphological, ultrastructural, immunophenotypic and functional characteristics

44
Q

What is the likely origin of hyalocytes, the main cell type in the vitreous?

A

yolk sac precursors such as the microglia

45
Q

What is the source of replenishment of hyaloid cells in the vitreous?

A

replenished at a low rate in the adult eye from bone marrow derived monocytes

46
Q

What is a marked vitreal cellular infiltrate indicative of?

A

pathological or inflammatory processes in adjacent tissues e.g. uveoretinitis

47
Q

What do the images show?

A

A = section of the inner retina in primate eye showing a hyalocyte

B = CD169+ hyalocytes in the rat subhyaloid space

ANATOMY2: Structure of the eye (14 decks)

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