Vitreous Flashcards
When does the vitreous begin to liquify (consistenty start change)?
The day we were born
How much of the vitreous is water?
98% water
What is the volume of the vitreous in the eye?
80% (largest structure)
How large is the vitreous chamber in a newborn? in an adult?
Newborn - 10.5 mm
Adult - 16.5 mm (13 years of ageO
The liquefaction of the vitreous is at 20% by what age? 50%?
20% - 18
50% - 80th decade
What are the non-aqueous components of the vitreous?
collagen and glucosaminoglycans (GAGs)
(form the vitreous into a viscoelastic gel)
What interactions does the existence of a gel in the vitreous depend on?
Interactions between the GAGs and collagen
The vitreous in ____% Type II collagen
75%
The vitreous is ~____% type V/XI collagen?
10%
The optic cup is occupoed but the ____ ____ in the early stages
lens vesicle
As the optic cup grows, the space is filled with? and secreted by?
Fibrillar material
Embryonic retina
Later in life, when the hyaloid artery penetrates the optic cup more _____________ ?
fibrillar material from blood vessel cells fills the space
The mass of the optic cup in the end is known as?
The primary vitreous
The size of the vitreous cavity _____ and the hyaloid vascular system ______ developing the _____ _____
Increases
regresses
secondary vitreous
The main hyaloid artery maintains for a period of time and then disappears and leave the _____ _____
Cloquet’s canal
Whay os the Cloquet’s canal?
A tube of primary vitreous surrounded by secondary vitreous running from the retrolental space to the optic nerve
Zonules are the _____ _____ that are developed from the _____ _____
Suspensor fibrils
Fibrillary material
What structures of the lens are termed the tertiary vitreous?
Zonules
The mature vitreous body is a _____ ____ that occupies the vitreous cavity
transparent gel
The mature vitreous body has what kind of shape except where?
spherical except at anterior end which in concave
What is the outermost oart of the vitreous called and what is it divided into?
Cortex
Posterior (100 um thick) and Anterior cortex
The vitreous base is __-dimensional and extends aprox. ____ anterior to the ora serrata to ____ posterior to the ora serrata
3
2 mm
3mm
Are the collagen fibrils in the base of the vitreous densely or losely packed?
Densely
What can the vitreoretinal interface be defined from electron microscopy as?
The outer part of the vitreous cortex (posterior hyaloids)
(includes anchroing fibrils of the vitrois body and the ILM of the retina)
The ILM is a retinal strucure that is between __ and __ thick
1 and 3 um
The ILM consists mostly of what type of collagen and ______?
Type IV collagen and proteoglycans
The ILM is considered the what of the Mueller cells?
basal lamina
Where is the vitrous cortex firmly attached to the ILM?
Vitrous base
around optic disc (weiss ring)
at the vessels
In the area surrounding the foveola (diameter of 500um)
Through OCT the preretinal strands (from ____ ____) were found in what percent of non-symptomatic cases?
posterior cortex
60%
The gel structure of the vitreous acts as a barrier against?
movement of solutes
How do substances in the vitreous move?
Diffusion or bulk flow
In diffusion, what can be used as a tracer substance?
Fluorescein
What is bulk flow in the vitreous cavity a result of?
Possible pressure gradient from anterior part of eye toward posterior
What form of movement is responsible for the movement of large, high molecular weight substances?
Bulk Flow
What is liquefaction of the vitreous gel structure also known as?
Synchysis
Where is synchysis most noteable?
In the center of the vitreous
When the gel structure of the vitreous is dissolved it is replaced with what?
Aqueous lacunae
What do the aqeous lacunae do over time?
Melt together
Does the vitreous collagen molecular weight increase or decrease with age? Why?
Increases
Because of the formation of new covalent cross-links between peptide chains
Why are proteins in the vitreous cross-linked?
Because of the Maillard reaction
What is the Maillard reaction
Formation of a covalent bond between amino groups and glucose leading to insoluble proteins
People with what disease tend to see accelerated Maillard reactions?
People with Diabetes mellitus (doubled)
The normal physiology of the vitreous body can be divided into what four groups?
- Support function for the retina and filling-up function of the vitreous body cavity
- Diffusion barrier between the anterior and the posterior segment of the eye
- Metabolic buffer function
- Establishment of an unhindered path of light
The intact vitreous body protects what?
The retina
An intact vitreous body, which fills up the entire vitreous cavity may do what for a retinal detachment?
May retard or prevent the development of a larger retinal detachment
The vitreous body can absord and reduce what>
Absorb external forces
Reduce mechanical deformation of the eye globe
What can lead to PVD (posterior vitreous detachment)
Central degeneration can lead to a collapse of the rest of the vitreous body, which causes the cortex to sink into the center of the vitreous body
If there is a stronf attachment between the posterior cortex and the ILM, a PVD can result in what?
A retinal tear
What is the first step in a rhegamatogenous retinal detachment?
retinal tear from PVD
PVD can induce ____ on the retina, especially in the ____ region
traction
foveal
An increase in the passive permeability or decrease in the outward active transport of the blood-retinal barrier may lead to?
Macular edema
Substances that are liberated from the anterior segment of the eye have difficulting reaching?
High concentrations in the posterior part of the eye because diffusion is slow and movement by bulk flow is limited in a gel
If the vitreous body is partly removed the exchange between the anterior and pasterior part of the eye is much ___ and ____
faster and easier
The preretinal oxygen tension is _____ in diabetic patients after vitrectomy, indicating what?
improved
increases with faster fluid currents
Can the vitreous act as a metabolic buffer and a reservoir for metabolism of the ciliary body and retina?
Yes
What can supplement the metabolism in the retina, especially in anoxic conditions?
Glucose and glycogen
Which Vitamin is present in the vitreous body in high concentrations?
Vitamin C
Vitamin C can act as a reservoir of antioxidants in which situations protecting the retina from?
Stress situations
Metabolic and light induced free radicals
Retina substances are diluted by diffusining into where?
The vitreous
The vitreous needs to maintain an ____ ____ which is produced by the low concentration of structural macromolecules
optimal transparency
Degeneration of the vitrous body interferes with what?
The path of light
What are some pathological conditions that interfere with transparency?
◦Synchysis scintillations
◦Asteroid degeneration
◦Hemorrhages
◦Inflammatory material
◦Fibrous tissue
◦Lack of regression of the hyaloid artery
True or False: Although the vitreous body can be removed and almost normal function of the eye will still be maintained, the vitreous body plays an important role in the physiology and pathophysiology of the eye.
True
