Vitreous Flashcards
What is the largest cavity of the eye?
the vitreous cavity
What proportion of the total volume of the eye is the vitreous cavity?
two thirds
What is the weight of the vitreous cavity?
3.9g
What is contained in the vitreous cavity?
vitreous humour or vitreous
What are the anterior and posterior boundaries of the vitreous cavity?
- anterior: lens, posterior lens zonules and ciliary body
- posterior: retinal cup
What is the vitreous?
transparent viscoelastic gel that i smore than 98% water with a refractive index of 1.33
What is the refractive index of the vitreous?
1.33
How does the viscosity of the vitreous compare to that of water?
it is 2-4x more viscous than water
What are the 6 main constituents of the vitreous?
- water
- hyaluronan (hyaluronic acid)
- collagens type II, VI, XI
- fibronectin
- fibrillin
- opticin
What are the 3 types of collagen within the vitreous?
- II
- VI
- XI
Which constituent of the vitreous is its gel structure dependent upon?
the collagenous constituents (not hyaluronan)
How are the collagen fibres arranged with the hyaluronan molecules in the vitreous gel?
the fine diameter type II collagen fibres (8-12 nm in diameter) entrap large coiled hyaluronan molecules
What is the overall shape of the vitreous?
shaped like a sphere with an anterior depression, the hyaloid fossa (also known as the patellar or lenticular fossa)
What are the two portions that the vitreous is traditionally regarded as consisting of?
- cortical zone
- central vitreous
How do the cortical zones and central vitreous differ microscopically?
cortical zone characterised by more densely arranged collagen fibrils
central vitreous is more liquid
How can the vitreous be further subdivided into major topographical zones, beyong the cortical zone and central vitreous?
3 zones:
- intermediate zone
- preretinal zone
- retrolental zone
What structures attach the cortical vitreous to points around its margin?
condensation of fine collagen fibrils
What are the 4 key points at which the cortical vitreous is attached to points around its margin?
- the peripheral retina and pars plana via the vitreous base, a 3-4mm wide band
- the posterior lens capsule (ligamentum hyaloide capsulare)
- the retina along the margins of the optic disc (base of the hyaloid canal)
- the inner limiting membrane of the retina, especially near retinal vessels
What is the name of the attachment of the vitreous to the posterior lens capsule?
ligamentum hyaloide capsulare
What is another way of referring to the point where the vitreous attaches to the retina along the optic disc margins?
base of the hyaloid canal
What attachment of the vitreous is disputed?
attachment to the retina along the margins of the optic dic (base of the hyaloid canal)
What is the most variable and weakest of the vitreous attachments?
the attachment to the inner limiting membrane of the retina, especially near the retinal vessels
What structure traverses the central vitreous?
central fluid-filled canal (hyaloid or Cloquet’s canal)
What does Cloquet’s (hyaloid) canal represent?
the remants of the course taken by the hyaloid artery that supplied both the vitreous and lens during embryogenesis and early fetal life
Which of the 3 major topographical zones of the vitreous are semi-liquid?
retrolental and intermediate zones
Why is the existence of an ordered, orgnised, vitreal structure still controversial?
problems of studying a gel that is 98.5-99.% water
At what age does the human vitreous begin to degenerate?
adolescence
What structures appear in the human vitreous once it begins to degenerate?
liquid-filled cavities and fibrillar strands such as the retrolental, preretinal and other named tracts of significance only to vitreal specialists
What are 5 major vitreous condensations that appear as the vitreous starts to degenerate in adolescence?
- rerolental tract
- preretinal tract
- vitreous base
- anterior hyaloid face
- vitreous cortex
What is the nature of most of the central vitreous tracts and which 1 is the exception?
most are mobile and change during eye movements
exception: preretinal
What may appear in the posterior vitreous cortex when the vitreous degenerates?
cortical holes, or pockets
Where do the ‘cortical holes’ or pockets in the posterior vitreous cortex occur, if present?
occur close to the fovea, retinal vessels and any developmental anomalies
What is the risk of cortical holes, or pockets, developing in the posterior vitreous cortex?
secondary pathological holes may develop following various disease processes
What is the name of the thin potential space between the surfce fo the cortical vitreous and the retina?
subhyaloid or sublaminar space
What may cause the subhyaloid (sublaminar) space between the cortical vitreous and retina to fill with fluid?
in cases of vitreous detachment
In what region may the vitreous detach relatively easily?
in the posterior segment where it is less weakly bound to the retina
In what scenario may fluid accumulate rapidly following vitreous detachment? When does it develop more slowly?
rhegmatogenous vitreous detachment
more slowly: where cortex is not ruptures (arrhegmatogenous vitreous detachment)
What type of change is cortex rupture in rhegmatogenous vitreous detachment?
age-related change in the vitreous detachment
What serious condition may vitreous detachment predispose to?
retinal detachment
Are there cells in the vitreous?
is essentially acellular however occasional isolated cells may occur in the cortex, particularly near the vitreous base, optic disc and retinal vessels
What are the three places in the vitreous cortex where isolated cells may occasionally occur?
- near vitreous base
- near optic disc
- near retinal vessels
What is the main cell type in the vitreous?
hyalocytes
What cells are hyalocytes, the main cell type in the vitreous, similar to and how?
macrophages: they have the same morphological, ultrastructural, immunophenotypic and functional characteristics
What is the likely origin of hyalocytes, the main cell type in the vitreous?
yolk sac precursors such as the microglia
What is the source of replenishment of hyaloid cells in the vitreous?
replenished at a low rate in the adult eye from bone marrow derived monocytes
What is a marked vitreal cellular infiltrate indicative of?
pathological or inflammatory processes in adjacent tissues e.g. uveoretinitis
What do the images show?
A = section of the inner retina in primate eye showing a hyalocyte
B = CD169+ hyalocytes in the rat subhyaloid space
