Flashcards in Vitreous Humor Deck (36):
Percentage of volume of eye is vitreous humor?
Length of vitreous chamber in newborn and adult?
Newborn= 10.5 mm
What percentage of the vitreous humor is water?
What are the non- aqueous parts of the vitreous?
collagen and GAGs (form the vitreous into a viscoelastic gel; Gel content decreases with age)
Liquification volume by age?
20% by age 18; greater than 50% by 80th decade; liquefication starts the day you are born
Volume and types of collagen in vitreous?
75% Type II collagen
10%Type V and XI collagen
What are difficulties with investigating the vitreous?
1. The tissue we are trying to visualize in order to define is designed to be invisible
2. Previous techniques are combined with artifacts, so it is hard to make interpretations on the true in vivo situation
Embryology of Primary Vitreous
1. optic disc occupied by lens vesicles
2. As cup grows space filled by fibrillar material (secreted by embryonic retina)
3. Hyaloid artery penetrates and even more fibrillar material fills space (from blood vessels)
Embryology of Secondary Vitreous
1. size of vitreous cavity increases
2. hyalod vascular system regresses
3. main hyaloid artery stays longer but eventually disappears
3. cloquet's canal takes its place
What is cloquet's canal?
a tube of primary vitreous surrounded by secondary vitreous running from the retrolental space to the optic nerve
Embryology of tertiary vitreous?
Zonules are the suspensor fibrils that are developed from the fibrillary material
Zonules of the lens are termed the tertiary vitreous
Describe mature vitreous
spherical except anterior where it is concave corresponding to the crystalline lens
Cortex of mature vitreous
The outermost part of the vitreous
divided into an anterior cortex and a posterior cortex, the latter being approximately 100 µm thick
Base of mature vitreous
a three-dimensional zone.
It extends approximately from 2 mm anterior to the ora serrata to 3 mm posterior to the ora serrata, and it is several mm thick.
The collagen fibrils are especially densely packed in this region.
the outer part of the vitreous cortex (posterior hyaloids), including anchoring fibrils of the vitreous body and the ILM of the retina.
Internal Limiting Membrane
1-3 microns thick
mainly type 4 collagen and proteoglycans
considered basal lamina of Muller cells
Locations vitreous cortex is attached to ILM?
- at vitreous base
- around optic nerves (Weiss ring)
- at the vessels
in area surrounding foveola
(see sparks; photorecptors rubbin against each other
OCT imgagng findings of vitreoretinal interface
Preretinal strands (from posterior cortex) were found in 60% of non-symptomatic cases
There was no biomicroscopic evidence of a posterior vitreous detachment (PVD)
Barriers against movements of solute
Substances move by?
What is used as a tracer substance in diffusion?
Result of a pressure gradient from the anterior to posterior pole of the eye
Large, high molecular weight substances move due to this gradient
Bulk flow does NOT play any significant role for distribution of low molecular weight substances in the vitreous
Main change: liquefacation of the gel structure; aka synchysis (This is most notable in the center of the vitreous)
Gel structure is dissolved and replaced with aqueous lacunae (these melt together)
4 Main Aspects of vitreous physiology?
1. Support function for the retina and filling-up function of the vitreous body cavity
2. Diffusion barrier between the anterior and the posterior segment of the eye
3. Metabolic buffer function
4. Establishment of an unhindered path of light
How does vitreous support retina?
- helps prevent large retinal detachment
- absorbs external forces to protect globe deformation
Posterior Vitreous Detachment (PVD)
The central degeneration is large and causes a collapse -> the cortex sinks to the center of the vitreous body
Considered a normal aging phenomena
Why does retinal tear result?
can result if there is a strong attachment between posterior cortex and the ILM
1st step in a rhegamatogenous retinal detachment
PVD can also induce traction on the retina, especially in the foveal region.
Normally, blood-retinal barrier is tight
Increased passive permeability and decreased outward active transport may lead to edema formation
Vitrectomy improves VA’s
Diffusion between anterior and posterior segments
Substances liberated from the anterior segment have difficulties reaching high concentrations in the posterior part of the eye
The vitreous gel also prevents topically administered substances from reaching the retina and optic nerve
After a removal of the lens and an anterior vitrectomy, exchange between the anterior and posterior part of the eye is fast and easy
After vitrectomy, the preretinal oxygen tension is improved in diabetic patients- so oxygen transport increases and retinal neovascularization and macular edema regress
How does vitreous act as a buffer?
The vitreous can act as a metabolic buffer and a reservoir for metabolism of the ciliary body and the retina
Glucose and glycogen can supplement the metabolism of the retina
Vitamin C is present in high concentrations and acts as a reservoir of antioxidants
(in stress situations, protecting the retina from metabolic- and light-induced free radicals.
Metabolic buffer play important role?
no; Because normal function of the retina can be obtained after total vitrectomy, the metabolic buffer functions of the vitreous do not seem to play an important role.
Retina substances are diluted by diffusing into the vitreous
If the vitreous acts as a diffusion barrier to retinally produced vasoproliferation. They are retained in high concentrations close to the retina- depends on the state of virtreous
What can vitrectomy cause?
a vitrectomy could also cause the vasoproliferative factors to move from the posterior to the anterior pole leading to neovascularization in the anterior segment
What interferes with path of light?
An important function is to maintain optical transparency, produced by a low concentration of structural macromolecules
Degeneration of the vitreous with generation of opacities interferes with the path of light
Pathological conditions that interfere with transparency?
Lack of regression of the hyaloid artery