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Physiology of the Eye > The Vitreous > Flashcards

Flashcards in The Vitreous Deck (27)
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1
Q

The vitreous is what % water?

A

98%

2
Q

What makes up the framework of the vitreous and provides its plasticity (propensity of a material to undergo permanent deformation under load)?

A

collagen

3
Q

What fills the spaces between the framework and gives the vitreous its viscoelasticity (possess both viscous and elastic properties when deformed)?

A

hyaluronic acid and water

4
Q

An increase/decrease in what will make the vitreous more gel-like/fluid?

A

amount of collagen

5
Q

What accounts for species variation in vitreal consistency?

A

collagen content (cortical areas generally contain more collagen)

6
Q

How does embryology vitreous differs from postnatal vitreous?

A

much more dense and opaque

7
Q

What happens to the vitreous after birth that makes the vitreous less dense and clear?

A

collagen content stays relatively the same, however hyaluronic acid concentration increase fourfold, dispersing the collagen fibrils and increasing the clarity of the vitreous (HA and water fill more spaces between the vitreous)

8
Q

What happens to the vitreous as it ages?

A

continue production of HA and dispersal of the collagen fibrils causes the vitreous to become liquefied with age.

9
Q

What happens to collagen bundles and hyaluronic acid as liquefaction of the vitreous progresses with age?

A

collagen bundles are packed into the remaining gel fraction, and HA molecules are redistributed to the liquid fraction

10
Q

What is a common complication of progressive virtual liquefaction, and what condition can this predispose to?

A

As the vitreous continue to liquify the posterior virtual cortex can separate from the internal limiting membrane. This predisposed to rhegmetogenous retinal detachment as forces along the vitreoretinal interface are altered.

11
Q

At what age in humans do rheologic changes in the central vitreous occur?

A

5 year

12
Q

In elderly human patients, how much of the vitreous is eventually liquefied?

A

more than 50%

13
Q

What % of the globe does the vitreous occupy?

A

80%

14
Q

How does the vitreous play a role in growth of the eye?

A
  • expansion of the vitreous aids in growth of the globe (removal of the vitreous prematurely lowers intravitreal pressure and stops growth of the eye)
  • goldfish use this to their advantage to help increase the refractive power of an eye submerged in water
15
Q

How does virtual elongation effect the refractive power of the eye?

A
  • vitreal elongation causes an increase in the axial length of the globe, which lengthens the path of incoming light, thus providing for greater light refraction
  • an increased axial length of the globe can also lead to axial myopia (has been demonstrated through visual deprivation in nonhuman primates, chickens, and the cat)
16
Q

What effects elongation of the vitreous?

A
  • the synthesis of collagen

- synthesis, molecular reconfiguration and hydration of HA molecules

17
Q

In humans, how might the vitreous aid in accommodation?

A

there is evidence that the vitreous moves anteriorly against the lens, changing the lens diameter and axial length

18
Q

What anatomic factors contribute to the optical clarity of the vitreous?

A
  • small diameter of virtual collagen fibers
  • wide dispersion of collagen fibers
  • relative acellularity
  • blood vitreous barrier
19
Q

What accounts for the blood vitreous barrier, and in what circumstances might it be disrupted?

A
  • HA molecules are though to act as a barrier preventing diffusion of macromolecules and cell into the vitreous
  • may be disrupted in trauma or cortex disruption
20
Q

The vitreous transmits 90% of light through what wavelengths?

A

300 and 1400 nm

21
Q

True or False: inflammatory responses, neovascularization, and collagenase activity are suppressed in the vitreous (likely as a function of the blood vitreous barrier).

A

true

22
Q

What are the two primary factors affecting diffusion of molecules through the vitreous?

A

hyaluronic acid concentration and molecule size

23
Q

What are some ways the vireos plays a role in ocular metabolism?

A
  • serves as a storage site for retinal metabolites such as glycogen, amino acids and potassium
  • acts as a depository for retinal and lenticular waste products such as lactic acid and free radicles (help protect the lens and retina from toxic compounds)
24
Q

In the cow, what size are pores in the vitreous?

A

400nm in diameter

25
Q

The vitreous provides both mechanics and structure support for what structures?

A

lens and retina

26
Q

The viscoelastic properties of the vitreous protect the internal eye structures during what activity, and what components of the vitreous contribute to its viscoelasticity?

A
  • protect the internal structures of the eye from trauma and stress, especially during rapid eye movement
  • the concentrations of collage and HA, as well as their cross linking, contribute to viscoelasticity
27
Q

How does the concentration of vitreal HA and collagen differ between the human and pig, and what property of the vitreous does this correspond to?

A
  • the concentration of vitreal HA and collagen is twice as high in the human eye compared to the pig
  • this corresponds to a 60% increase in the Spring constant (measure of elasticity) in the human vs pig vitreous