The Vitreous Humour Flashcards
(29 cards)
Know the anatomy of the human vitreous
ok
Give 4 physiological functions of the vitreous
-maintains transparency to visible light by excluding cells and large molecules
-cloquets canal for metabolic processes of the lens
-coordinates eye growth
-protects eye in mechanical trauma
what are the 3 main parts of the vitreous
-central vitreous
-basal vitreous
-vitreous cortex
where is the canal of clouquet in the vitreous?
In the central vitreous
what is the fibril insertion in the central vitreous like and what’s its conc. compared to the basal and cortical vitreous
runs anteriorly into vitreous base and posteriorly into vitreous cortex
lower in conc. here than in basal and cortical vitreous
what is the main GAG in the central vitreous?
hyaluronic acid
how does the vitrous base extend?
1-2 mm anterior to ora serrata
3-4mm prosterior to ora serrata
what part of the vitreous cortex is in direct contact with the aqueous?
the anterior vitreous cortex
what chemicals make up the vitreous cortex?
hyalocytes, collagen, hyaluronic acid, chondroitin sulphate in higher concentration than in central vitreous
how does the posterior vitreous sit on the retina?
-attached indirectly to inner limiting lamina of the retina
-adherent to retina
-absent at the optic disk
-thinned over the macula
what is the vitreous composed of?
-hyalocytes in base and cortex, otherwise acellular
-98% water
-GAGs of hyaluronan
-unbranched collagen fibrils
-salts
what are the three main vitreous properties?
-transparent
-non-compressible
-very viscoelastic: allows deformation with rapid restoration by acting as a shock absorber and slow diffusion of fluid
what pathological condition are hyalocytes associated with?
proliferative vitreoretinopathy
what go glycosaminoglycans GAGs bind with to form what?
proteins to form proteoglycans
what three GAGs are found in the vitreous
hyaluronan
chondroitin sulphate
heparan sulphate
Give 5 functions of hyaluronan
-forms space filling networks
-osmotic buffer
-molecular sieve excluding large molecules and cells
-lubricant
-forms viscoelastic solution that flows
how does collagen conc vary in the vitreous?
-highest at the vitreous base
-decreases towards central and posterior
-increases at cortical
what is the function of opticin in the vitreous?
prevents aggregation of collagen fibrils
give 4 non collagenous structural proteins in the vitreous
-fibrillin
-opticin
-VIT1
-fibronectin
what’s the significance of liquefaction and the vitreous?
liquid in the vitrious increases steadily with age and by age 80-90, >50% of vitreous is liquid
give the mechanism of vitreous liquefaction
-initially occurs in pockets
-triggers like light, photosensitizers, fe ions cu ions and vitamin C cause reactive O2 species
-oxidation of proteins
-proteins cross-link
-appearance of collagen fibril aggregates
-‘floaters’
-hyaluronan polymers degraded
-leads to progressive loss of lattice structure
-re-distribution of collagen leaves areas devoid of collagen
what can vitreous liquefaction be secondary to?
-inflammation
-infection
-tumour
-high myopia
How does vitreous liquefaction lead to posterior vitreous detachment?
-pockets of liquid come together
-collagen fibres aggregate so conc of hyaluronic acid is the same
-adhesion at vitreoretinal interface weakens
-PVD
what is the most probable cause of flashes
stimulation of the retina by vitreoretinal traction
