Flashcards in Chapter 11: Vitreous Deck (17):
What are the functions of the vitreous?
- transparent gel occupying major volume of globe
- conduit for nutrients and other solutes to adn from lens
What is the vitreous?
It is a gel composed of a collagen framework interspered with hydrated hyaluronan (contributes to the viscosity and stabilizes the collagen network)
What is the composition of the vitreous?
98% H20 and 0.15% macromolecules
also contains noncollagentous structural proteins and glycoproteins, hyaluronidase, and MMP-2
What types of collagen are found in the vitreous?
Type II= major collagen type, forms major component of the collagen fibrils
Type IX: found on the surface of the fibrils
Type V/XI--unique to the vitreous, location undetermined
Where the sites of attachment for the vitreous?
Margins of Optic Nerve disc
Loosely attached at ILM
What is the function of hyaluronan in the vitreous?
it is a weak polyanion with an affinity for h20 that contributes to the viscosity and provides structural support to the collagen network.
What is the major soluble protein of the vitreous? What is the second major soluble protein? Where are they derived from?
Albumin is the major soluble protein of the vitreous, and it is thought to be derived from the plasma.
Transferrin is the second major soluble vitreous protein, and is thought to be derived from the CB
By age 80-90, what percent of the vitreous has liquified?
50% of the vitreous will have liquified by age 80-90.
Myopia is associated with faster liquefaction
What is the process by which the vitreous undergoes liquefaction?
The crucial component is the breakdown of thin (12-15 micrometer) collagen filbrils into smaller fragments (2/2 age-related loss of type IX collagen). These small fibers than aggregate into thick fibrillar "opacities"
What is the definition of a Posterior Vitreous Detachment?
Separation of the cortical vitreous from the ILM
What affect does axial length of the eye have on concentrations of collagen and hyaluronan in the vitreous?
With an axial length > 26 mm, the concentrations of collagen and hyaluronan decrease by 20-30% compared to emmetropic eyes
How does the vitreous inhibit angiogenesis?
Anti-angiogeneic properties of the vitreous are due to it containing thrombospondin-1, pigment-derived face, and Opticin.
Why do the physiologic changes occur in the eye after a vitrectomy?
They occur due to an altered viscosity of the vitreous (200-3000x decrease in viscosity)
What are the physiologic changes that occur after a vitrectomy?
More rapid movement of 02, flattening of 02 gradient b/w anterior (usually better oxygenated) and posterior vitreous, increased retinal 02 tension
Increased posterior pole 02 tension thought to play a role in post-vitrectomy cataractogenesis
What happens when platelets come into contact with the vitreous?
Platelets induce aggregation and clot formation, which causes a phagocytic inflammatory reaction and liquefaction of the vitreous
How do macular holes relate to the vitreous?
Macular holes can sometimes originate from traction 2/2 attachment of the vitreous (specifically at the fovea)