Physiology Of Vitreous Flashcards
Largest organ of the eye
Vitreous
Vitreous transmits _____ of light
90%
Location of vitreous
Between lens and the retina
3 zones of the vitreous
Outermost: vitreous cortex (hyaloid cortex)
Center zone: cloquets canal
Intermediate zone: inner to the cortex and surrounds the center canal
Vitreous attachment to the retina
Vitreous attached to ILM of retina by the membrane limitans interna (MLI)
Vitreous base
- Located at ora serrata
- 1.5mm broad annular region
- attached to NPE of ciliary body and the ILM of the peripheral retina
- strongest attachment
- no age declined
What is the strongest vitreal attachment to the retina
Vitreal base at the ora serrata
Wiegers ligament (rettrolental ligament)
- between the posterior surface of the lens and the anterior surface of the vitreous
- firm attachment
- declined with age
- creates burgers space on the back of the lens
- space between vitreous and lens
Peripapillary adehsion of vitreous
- around the edge of the optic disc
- medium attachment
- declined with aging
Weiss ring in vitreal detachment
Macular and peripheral retinal attachment of vitreous
- weak attachment
- findings are controversial for macular attachment
- some individuals may have an attachment 3-5mm posterior to the vitreous base. Attach to retinal blood vessels
Composition of vitreous
- water major component
- collagen type II
- HA
- vitreal cells
- vitamin C
Does have other substances too
Vitreous collagen fibers and HA
The gel structure of the vitreous results from the arrangement of collagen fibrils suspended in a network of HA
Hyalocytes
- majority
- synthesize glycoproteins for the collagen fibrils
- synthesize HA
What cells synthesize HA
Hyalocytes
Vitreal cells
Hyalocytes
Fibrocytes
Macrophages
Vitreous functions
Support for retina
Diffusion barrier
Metabolic barrier
Transparency
Support function of vitreous
- prevents retinal detachment
- reduced mechanical deformation
- supports lens during trauma
- decreases transmission of light at 300-350nm
- mechanical support of limited signicance
Posterior vitreous detachment (PVD)
- 10% of eyes have strong vitreous retina attachments
- vitreous traction can cause retinal tears
- possibility of vitreous hemorrhage’s
- high risk of rhegmatogenous retinal detachment
Normal aging process
Most common pathology of vitreous
PVD
Macular edema
- in some cases
- vitreous-retinal traction
- increase in passive permeability
- decrease in active transport across blood retinal barrier
- increased osmotic pressure
Causes of macular edema
Retinal ischemia
Vitreal traction
Diffusion barrier function of vitreous
- slow diffusion actress vitreous
- bulk flow is limited across veitrous
- prevents topically adminstered substance from reaching the retina
- prevents substances in blood stream from reaching vitreous center
- no diffusion barrier for small molecules
Diffusion in the vitreous
Slow
- bulk flow is limited
- Abx drops cannot pass though the vitreous into the posterior part of the eye
Metabolic buffer of vitreous
Contains a lot of substances like glycogen, glucose, nutrients for retinal metabolism
Reservoir for vitamin C (ascorbic acid)
