Vitreous Humor

Question 1

Percentage of volume of eye is vitreous humor?

Answer 1

80% (largest)

Question 2

Length of vitreous chamber in newborn and adult?

Answer 2

Newborn= 10.5 mm
Adult= 16.5

Question 3

What percentage of the vitreous humor is water?

Answer 3

98%

Question 4

What are the non- aqueous parts of the vitreous?

Answer 4

collagen and GAGs (form the vitreous into a viscoelastic gel; Gel content decreases with age)

Question 5

Liquification volume by age?

Answer 5

20% by age 18; greater than 50% by 80th decade; liquefication starts the day you are born

Question 6

Volume and types of collagen in vitreous?

Answer 6

75% Type II collagen

10%Type V and XI collagen

Question 7

What are difficulties with investigating the vitreous?

Answer 7

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

Question 8

Embryology of Primary Vitreous

Answer 8

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)

Question 9

Embryology of Secondary Vitreous

Answer 9

1. size of vitreous cavity increases
2. hyalod vascular system regresses
3. main hyaloid artery stays longer but eventually disappears
4. cloquet’s canal takes its place

Question 10

What is cloquet’s canal?

Answer 10

a tube of primary vitreous surrounded by secondary vitreous running from the retrolental space to the optic nerve

Question 11

Embryology of tertiary vitreous?

Answer 11

Zonules are the suspensor fibrils that are developed from the fibrillary material
Zonules of the lens are termed the tertiary vitreous

Question 12

Describe mature vitreous

Answer 12

transparent gel

spherical except anterior where it is concave corresponding to the crystalline lens

Question 13

Cortex of mature vitreous

Answer 13

The outermost part of the vitreous

divided into an anterior cortex and a posterior cortex, the latter being approximately 100 µm thick

Question 14

Base of mature vitreous

Answer 14

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.

Question 15

Vitreoretinal Interface

Answer 15

the outer part of the vitreous cortex (posterior hyaloids), including anchoring fibrils of the vitreous body and the ILM of the retina.

Question 16

Internal Limiting Membrane

Answer 16

1-3 microns thick
mainly type 4 collagen and proteoglycans
considered basal lamina of Muller cells

Question 17

Locations vitreous cortex is attached to ILM?

Answer 17

• at vitreous base
• around optic nerves (Weiss ring)
• at the vessels
  in area surrounding foveola
  (see sparks; photorecptors rubbin against each other

Question 18

OCT imgagng findings of vitreoretinal interface

Answer 18

Preretinal strands (from posterior cortex) were found in 60% of non-symptomatic cases
There was no biomicroscopic evidence of a posterior vitreous detachment (PVD)

Question 19

Barriers against movements of solute

Answer 19

gel structures

Question 20

Substances move by?

Answer 20

diffusion

bulk flow

Question 21

What is used as a tracer substance in diffusion?

Answer 21

fluorescein

Question 22

Bulk Flow

Answer 22

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

Question 23

Aging Effects

Answer 23

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)

Question 24

4 Main Aspects of vitreous physiology?

Answer 24

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

Question 25

How does vitreous support retina?

Answer 25

• helps prevent large retinal detachment
• ## absorbs external forces to protect globe deformation

Question 26

Posterior Vitreous Detachment (PVD)

Answer 26

The central degeneration is large and causes a collapse -> the cortex sinks to the center of the vitreous body
Considered a normal aging phenomena

Question 27

Why does retinal tear result?

Answer 27

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.

Question 28

Macular Edema

Answer 28

Normally, blood-retinal barrier is tight
Increased passive permeability and decreased outward active transport may lead to edema formation
Vitrectomy improves VA’s

Question 29

Diffusion between anterior and posterior segments

Answer 29

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

Question 30

Diffusion work?

Answer 30

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

Question 31

How does vitreous act as a buffer?

Answer 31

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.
)

Question 32

Metabolic buffer play important role?

Answer 32

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

Question 33

What can vitrectomy cause?

Answer 33

a vitrectomy could also cause the vasoproliferative factors to move from the posterior to the anterior pole leading to neovascularization in the anterior segment

Question 34

What interferes with path of light?

Answer 34

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

Question 35

Pathological conditions that interfere with transparency?

Answer 35

Synchysis scintillations
Asteroid degeneration
Hemorrhages
Inflammatory material
Fibrous tissue
Lack of regression of the hyaloid artery

Question 36

Vitreous Humor Main Point

Answer 36

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!