vitreous physiology

vitreous volume, what percentage is water

4 ml

•Comprised of 99% H20

vitreous comprises ___% of the globe

80 --> largest structure in eye

2 zones of vitreous

cortex = outside

medullary = inside

what portion of vitreous contains hyalocytes

cortical vitreous

what portion of vitreous contains anterior and posterior hyaloid

cortical vitreous

what zone of vitreous has aging changes first?

medullary --> becomes liquified

acellular vitreous zone

medullary vitreous

what keeps outer vitreous attached?

vitreous fibers Blend within basal lamina of CB epithelium and retinal Müller cells of ILM

Firmest attachment of the vitreous & retina in the region of the____

ora serrata

___ divides anterior hyaloid from posterior hyaloid

vitreous base (firmest attachment at ora)

strongest to weakest vitreous attachements

vitreous base (ora)

•Posterior Lens

•optic disc

•macula

•weakest - retinal vessels

what causes weiss ring

vitreous detachment at optic disc

soluble and insoluble components of vitreous

solube (vitreous humor) = HA, ascorbic acid, sugar, electrolytes

insoluble (residual proteins) = collagen

Vitreous has a gel structure due to

long, thick, nonbranching collagen fibers suspended in hyaluronic acid (HA)

•Viscoelastic properties of vitreous =

HA + Collagen fibrils

hyalocytes functions

synthesize HA and collagen type II

highest concentration of collagen is in the

cortex (where hyalocytes are)

describe HA

highly hydrophilic --> retains water

•MAIN VISCOSITY REDUCING AGENT IN VITREOUS

ascorbic acid --> Increases HA depolymerization

•Vitreous volume ___ from birth to adulthood

DOUBLES

Gel-Sol Transformation

liquefaction of vitreous associated with aging (from gel to soluble material)

Liquefaction of vitreous due to

depolymerization (loose water) of HA and collapse/structural changes of collagen framework

collagen Molecular weight ____ with age due to ___

-Molecular weight increases with age due to the formation of new covalent cross-links between peptide chains (less spacing btw them bc HA looses water)

____ vitreous is the first to liquefy (lacunae/water pockets)

Central (Medullary)

as medullary vitreous liquifies there is simultaneous ___ of collagen fibrils

Simultaneous syneresis/shrinkage/ collapse of collagen fibrils

describe the steps that lead to PVD

1. vitreous liquifies: HA depolymerization --> water molecules detach

2. water pooling in meullary vitreous

3. partial PVD --> vitreous fibers and ILM muller cells detach at weakest attachemnt (retinal BVs)

4. complete PVD --> detach up to vitreous base (ora)

•Factors contributing to breakdown of HA-collagen complex:

-Normal aging

-High axial myopia

-Aphakics

-Intraocular Inflammation

PVD is separation of posterior vitreous from the ___

ILM of the retina muller cells

complete PVD occurs where?

posterior to vitreous base (ora), anterior to vitreous base = anterior vitreous

___% of aphakic eyes have PVD

100

who gets PVD more:

female vs male

intracapsular cataract extract vs extracapsular

female > male

ICCE > ECCE

how does ILM aging changes contribute to PVD

ILM thickens with age and does not adequately hold inserted collagen fibers

•As vitreous pulls away from retina, it can also cause:

-Floaters

-Flashes (vitreoretinal traction)

-Retinal hemorrhage

-Vitreous hemorrhage

-Retinal tear

-Potential for retinal detachment

order of PVD locations

1. retinal BV (weakest attach)

2. macular

3. ONH

anomalous PVD

vitreous stays attached at macula --> can cause macular hole

vitreous base detachment most often occurs in ___

inferior temporal quadrant

macular hole formation is the result of

foveal attachment plaques

•Strong areas of adhesion b/t vitreous cortex & ILM

PVD stays attached at macula and pulls off

epiretinal membrane cause

-PVD causes disruption of ILM

-Retinal glial cells migrate through ILM

-Glia proliferate on retinal surface

•Stimulates RPE migration/proliferation

-Glia & RPE give macula a shiny/puckered appearance

what causes asteroid hyalosis

•white or yellowish-white bodies (calcium soaps) that are tightly adherent to vitreous collagen strands

cholesterol crystals that are free flowing in vitreous occur in

Synchysis Scintillans