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Ocular Physiology 2 > Vitreous > Flashcards

Vitreous Flashcards

1
Q

How much percentage wise does the vitreous take over

A

80% of the volume of the eye and is the largest single structure of the eye

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2
Q

How many mm is the vitreous chamber in a newborn? What about an adult?

A

Newborn: 10.5 mm
Adult: 16.5 mm

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3
Q

How much water is in the vitreous?

A

98% water

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4
Q

What are the non aqueous components of the vitreous

A

Collagen and GAGs form the vitreous into a viscoelastic gel

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5
Q

T/F gel content decreases with age

A

True

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6
Q

what types of collagen are in the vitreous?

A

Type II collagen: 75%

Type V and VI: 10%

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7
Q

What are some difficulties that arise when investigating the vitreous

A
  1. Vitreous is supposed to be invisible

2. Previous techniques are combined with artifacts, so its hard to make interpretations on the true in vivo situation

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8
Q

What is the embryology of the vitreous

A
  1. The optic cup is occupied by the lens vesicle
  2. The cup grows and the space is filled by fibrillar material secreted by embryonic retina
  3. The hyaloid artery penetrates and more fibrillar material from blood vessel cells fills the space
  4. the mass in the end is the primary vitreous
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9
Q

How does the second vitreous form

A
  1. The size of the vitreous cavity increases and the hyaloid vascular system regresses
  2. Main hyaloid artery maintains for a period of time then disappears and leaves the cloquet’s canal
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10
Q

What is Cloquet’s canal

A

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

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11
Q

What refers to tertiary vitreous

A

Zonules of the lens, which are the suspensor fibrils that are developed from the fibrillary material

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12
Q

What is the mature vitreous body

A

A transparent gel that occupies the vitreous cavity. It has a spherical appearance, except for the anterior part, which is concave

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13
Q

What is the outermost part of the vitreous

A

Cortex; divided into an anterior and posterior cortex

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14
Q

What does the base consist of

A

Base; 3 dimensional zone extending from 2 mm anterior to 3 mm posterior to the ora serrata. This is where the collagen fibrils are densely packed

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15
Q

What makes up the outer part of the cortex?

A

The Vitreoretinal interface, which includes the retina and ILM (internal limiting membrane) and anchoring fibrils of the body

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16
Q

What type of collagen makes up the ILM

A

type IV collagen and proteglycans; considered the basal lamina of the Mueller cells

17
Q

Where are the various locations that the vitreous cortex is firmly attached to

A
  1. At the vitreous base
  2. Around the optic disc (Weiss ring)
  3. At the vessels
  4. In the area surrounding the foveola
18
Q

What do OCT findings show

A

That in 60% patients there are preretinal strands which are the first signs/precursors to detachment. Patient has no idea. This is asymptomatic

19
Q

If foveal anatomy is not the same what happens with the patient

A
  • Distortion occurs

- but patient sees 20/20. VA does not got down!

20
Q

Ascorbic is greater in the vitreous than in the blood.

A

True

21
Q

What is the vitreous’ primary job

A

To act as a buffer

22
Q

What is the same thing as Glycasaminoglycans

A

Hylaranic acid/ hyalourin which there is a lot in vitreous

23
Q

what does the gel structure act as a barrier against

A

The movement of solutes by diffusion or bulk flow

24
Q

When does bulk flow happen

A

happens as a result of possible pressure gradient from the anterior part of the eye toward the posterior pole of the eye. Only high, large molecular weight substances move due to this gradient

25
Q

What is the main change in aging effects in regards to the vitreous

A

Main change: Liquification of the gel structure aka SYNCHYSIS, most notable in the center of the vitreous. The gel structure is dissolved and replaced with aqueous lacunae

26
Q

What are other aging effects in regards to the vitreous

A

Vitreous collagen molecular weight increases with age because of the formation of new covalent cross links between the peptide chains.

27
Q

What is the Mailard reaction

A

Proteins are cross linked because of this - insoluble proteins produced by a covalent bond between an amino group and glucose

28
Q

What are the 4 main aspects of the vitreous

A
  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
29
Q

How does the vitreous support the retina?

A

Helps prevent a large retinal detachment and absorbs external forces to protect globe deformation

30
Q

What is a posterior vitreous detachment

A

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

31
Q

How does a retinal tear occur

A

When there is a strong attachment between posterior cortex and the ILM. The first step is rhegamatogenous retinal detachment; a tear occurs

32
Q

How does macular edema occur

A

Increased passive permeability and decreased outward active transport. Retina starts leaking, vitreous doesnt allow it to escape, increasing macular edema. Take out vitreous to help this

33
Q

What are good things and bad things if gel is removed

A

Some substances can reach the retina and optic nerve. Good outcome is that glucose and antioxidants go back to the retina. Bad is that you can have pathology that can reach the back of the eye

34
Q

The vitreous also acts as a metabolic buffer and reservoir for the ____ and ____

A

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

35
Q

Does the vitreous play an important role as a buffer?

A

No, normal function of the retina can be obtained after total vitrectomy

36
Q

What could cause neovascularization in the anterior segment of the eye

A

With a vitrerectomy, you get vasoproliferative factors to move from the posterior to the anterior pole

37
Q

What are some pathological conditions that interfere with transparency:

A
  1. Synchysis scintillations
  2. Asteroid degeneration
  3. Hemorrhages
  4. Inflammatory material
  5. Fibrous tissue
  6. Lack of regression of the hyaloid artery

Ocular Physiology 2 (8 decks)

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