Vitreous Humor Flashcards
What percent if the eye is occupied by vitreous
And was is its volume
Approx 80%
And approximately 4.5ml in volume
What is the vitrous humor
Gel like substance that fills up the space between lens and retina
Function of hyaloid/ cloquet’s canal
Embryonic development of the eye, facilitating transport of nutrients to developing structures
What are the three types of vitreous
Central vitreous
Basal vitreous
Vitreous cortex
What is the thickness of vitreous cortex
100-300 micrometers
What is the direction of the posterior vitreous cortex
Runs parallel to the retina
Which part of retina is the vitreous cortex absent
Optic disk
Why is vitreous thinned at the macula
For optical clarity
What are the main components of vitreous
Water
Soluble proteins
GAGs
Glycoproteins
Electrolytes/ salts
Main properties of vitreous humor
Transparency
Highly hydrated gel
Avascular ie lacks blood vessels
Highly viscoelastic
Non compressible
What percentage of vitreous is water
More than 98%
Which type of vitreous is not acellular
Basal vitreous
Vitreous cortex
What type of cells are found in the vitreous humor
Hyalocytes
Function of hyalocytes
Synthesis and maintenance of hyaluronic acid
What are the main carbohydrates and, proteins present in vitreous
Carbohydrates- glycosaminoglycans (GAGs)
Proteins- collagens
Describe the changes in hyaluronan concentration with age
Increases up to 20 years
Constant until 70 years
Increases 70+ years
Which part of vitreous contains
1. Lowest hyaluronan
2. Highest hyaluronan
Lowest- central vitreous
Highest- posterior vitreous
What is the main collagen present in vitreous
Collagen II (75%)
Where in the vitreous, is the concentration of collagen at
1. Its highest
2. Its lowest
Highest- vitreous base
Lowest- central
When in the human embryonic life does synthesis of the adult-type vitreous begin
Sixth week
What is vitreous liquefaction
Process in which the gel -like vitreous humor in the eye becomes more liquid/ less gel like in consistency
Around 80-90 years old, what percentage of the vitreous gel has turned into liquid
50%+
What are some mechanisms of vitreous liquefaction
Collagen breakdown leads to the loss of structural intergrity
Water content changes
Enzymes- can cause breakdown of structural proteins
Cross linking of proteins
What is syneresis
Contracting and shrinkage of the gel, leading to the release of fluid and changes in the vitreous structure
How does liquefaction lead to posterior vitreous detachment
Pockets of liquid coalesce leading to the gel shrinking
As the vitreous contracts, vitreoretina adhesions are weakened, leading to vitreous pulling away from retina
What percentage of people over 65years have PVD
About 70%
What other comditions increases risk of PVD esp in younger age
High myopia
Traumatic injuries eg retinal tear, vitreous haemorrhage
What is the cause of most physiologic floaters
Small amounts of debris present in the vitreous, from the embryonic hyaloid vascular system
Causes of other floaters
Collagen fibrils clumping together
Vitreous hemorrhage
Release of debris from infectious conditions eg uveitis
What is the function of vitreous
Coordinating eye growth
Protects eye during mechanical trauma
Maintains eye shape
Refractive properties
Common complications of PVD
Retinal tears
Macula hole
Retinal detachment
What are some causes of the perception of flashing lights
PVD
Retinal traction/tears
Retinal detachment
What is the most abundant macromolecule in the vitreous
Hyaluronic acid
