OAH - Vitreous

The vitreous is...

- Inert
- Transparent
- Hydrophilic
- Colorless

What is the largest and simplest single piece of connective tissue?

The vitreous

What is the axial length of the vitreous?

16.5mm

What is the vitreous volume?

4mL

What is a source of ascorbic acid?

The vitreous

What is the vitreous anteriorly?

Concave

What is the vitreous posteriorly?

Spherical

All surfaces contacting the vitreous are....

Basement membranes

What are the 2 vitreous zones?

- Cortical
- Medullary

The cortical vitreous is...

Tightly packed randomly arranged collagen fibers

The anterior cortical vitreous is...

Adjacent to the posterior lens and pars plana

The posterior cortical vitreous is...

Adjacent to the retina and contains tranvitreal holes

The posterior cortical vitreous contains...

- Prepapillary hole
- Premacular hole
- Prevascular fissure

Hyalocytes are the...

Metabolic center in the cortical vitreous

The medullary vitreous is...

Acellular and contains less fibres

The medullary vitreous liquifies with...

Age

Is the medullary vitreous metabolically active?

No

Vitreous fibres in the medullary section are....

Parallel, blending in with the basal lamina of the CB epithelium and Muller cells

What is the limiting membrane?

The anterior hyaloid

Where are hyalociliary zonules?

In the anterior hyaloid membrane between ciliary processes

What is a firm attachment site in the young?

Wiegers ligament

Strength of Wiegers ligament diminishes after...

35

How wide is the annular attachment formed by Wiegers ligament?

1 to 2mm wide and 8 to 9mm in diameter

Wiegers ligament is present between the..

Posterior lens surface and anterior vitreous face

Where is Bergers space?

Between 2 Wiegers ligaments

Why is Bergers space present?

Because the lens and vitreous are juxtaposed and not joined

Where is the coronary ligament?

The anterior hyaloid membrane to the posterior 1/3 of the ciliary processes

The median ligament spans from the....

Anterior hyaloid membrane to the pars plana

What does the vitreous base separate?

The anterior hyaloid from the posterior hyaloid

The vitreous base extends...

1.5mm anterior to the ora serrate and 2.5mm posterior

The vitreous base has the...

Firmest attachment due to a high density of fibrils

Where is the ILM thinner?

The are overlying the vitreous base

What does the posterior hyaloid contain?

Densely packed collagen that is parallel to the retina with few fibrils arranged at a right angle

The posterior hyaloid is adherent to the....

ILM of the retina

The posterior hyaloid has attachments to the...

- Retina
- Optic nerve
- Macula
- Vasculature

Perpendicular collagen fibrils insert into the ILM in the...

Vitreoretinal interface

What layers of the ILM do perpendicular fibres insert into?

- Lamina densa
- Lamina lucida

What are the 5 glue substances?

- Fibronectin
- Laminin
- Opticin
- Chondroitin sulfate
- Heparan sulfate

What is the weakest attachment area?

Retinal vessels

What is the 3 zone classification?

- Preretinal
- Intermediate
- Prehyaloid

Cloquets canal is a....

Hyaloid channel or retrolental tract

Cloquets canal represents the....

Former site of the hyaloid artery system

Where does cloquets canal start?

Bergers space

Where does cloquets canal end?

The area of Martegiani around the optic nerve

When does the primary vitreous form?

At the 4th to 6th week of development

The hyaloid artery system goes from the...

- Dorsal ophthalmic artery
- Hyaloid artery
- VHP
- PTVL

What does the PTVL nourish?

The developing posterior lens

The secondary vitreous forms during...

The 6th to 3rd month of development

When does the tertiary vitreous form?

During the 3rd to 6th month of development

What happens postnatally?

- HA increase leading to increased volume
- We have remnants of glial tissue, mittendorf dots, floaters, PHPV

What is the collagen in vitreous?

Type 2, insoluble

What is the soluble portion of the vitreous?

- HA
- Other metabolites

What does type 2 collagen look like?

- Long
- Thick
- Nonbranching

What makes type 2 collagen?

Hyalocytes in the granular ER

What does type 2 provide?

- Firmness
- Rigidity
- Stiffness
- Tensile resistance
- Transparency

Where is type 2 concentration the highest?

In the cortex vitreous base

Where is type 2 concentration the least?

In the medulla

What makes HA?

Hyalocytes

What does HA look like?

Long, unbranched MPS chains that fill spaces between collagen

HA is very....

Hydrophilic

What does HA reinforce?

The collagen network

HA retains water for...

- Rigidity
- Viscosity

What does HA control?

Diffusion of particles through the vitreous

What is the overall structure of vitreous?

Long, non branching collagen fibrils suspended in HA

What gives the vitreous viscoelastic properties?

- HA
- Collagen

Hyalocytes are...

Single, widely spaced cells in the cortex near the virtual surface

What is the predominant cell type in the vitreous?

Hyalocytes

What do hyalocytes do?

- They create HA and glycoproteins for collagen fibrils
- They phagocytose

What does ascorbic acid do?

- Scavenges radicals
- Absorbs UV light
- Reduces viscosity

What do sugars do?

- Aid in hyalocyte metabolism
- Diffuse from circulation or the posterior AQ

What are some electrolytes in the vitreous?

- Na
- K
- Cl
- HCO3
- Ca2
- Phosphates
- Lactic acids