Vitreous Humor

Question 1

What percent if the eye is occupied by vitreous
And was is its volume

Answer 1

Approx 80%
And approximately 4.5ml in volume

Question 2

What is the vitrous humor

Answer 2

Gel like substance that fills up the space between lens and retina

Question 3

Function of hyaloid/ cloquet’s canal

Answer 3

Embryonic development of the eye, facilitating transport of nutrients to developing structures

Question 4

What are the three types of vitreous

Answer 4

Central vitreous
Basal vitreous
Vitreous cortex

Question 5

What is the thickness of vitreous cortex

Answer 5

100-300 micrometers

Question 6

What is the direction of the posterior vitreous cortex

Answer 6

Runs parallel to the retina

Question 7

Which part of retina is the vitreous cortex absent

Answer 7

Optic disk

Question 8

Why is vitreous thinned at the macula

Answer 8

For optical clarity

Question 9

What are the main components of vitreous

Answer 9

Water
Soluble proteins
GAGs
Glycoproteins
Electrolytes/ salts

Question 10

Main properties of vitreous humor

Answer 10

Transparency
Highly hydrated gel
Avascular ie lacks blood vessels
Highly viscoelastic
Non compressible

Question 11

What percentage of vitreous is water

Answer 11

More than 98%

Question 12

Which type of vitreous is not acellular

Answer 12

Basal vitreous
Vitreous cortex

Question 13

What type of cells are found in the vitreous humor

Answer 13

Hyalocytes

Question 14

Function of hyalocytes

Answer 14

Synthesis and maintenance of hyaluronic acid

Question 15

What are the main carbohydrates and, proteins present in vitreous

Answer 15

Carbohydrates- glycosaminoglycans (GAGs)
Proteins- collagens

Question 16

Describe the changes in hyaluronan concentration with age

Answer 16

Increases up to 20 years
Constant until 70 years
Increases 70+ years

Question 17

Which part of vitreous contains
1. Lowest hyaluronan
2. Highest hyaluronan

Answer 17

Lowest- central vitreous
Highest- posterior vitreous

Question 18

What is the main collagen present in vitreous

Answer 18

Collagen II (75%)

Question 19

Where in the vitreous, is the concentration of collagen at
1. Its highest
2. Its lowest

Answer 19

Highest- vitreous base
Lowest- central

Question 20

When in the human embryonic life does synthesis of the adult-type vitreous begin

Answer 20

Sixth week

Question 21

What is vitreous liquefaction

Answer 21

Process in which the gel -like vitreous humor in the eye becomes more liquid/ less gel like in consistency

Question 22

Around 80-90 years old, what percentage of the vitreous gel has turned into liquid

Answer 22

50%+

Question 23

What are some mechanisms of vitreous liquefaction

Answer 23

Collagen breakdown leads to the loss of structural intergrity
Water content changes
Enzymes- can cause breakdown of structural proteins
Cross linking of proteins

Question 24

What is syneresis

Answer 24

Contracting and shrinkage of the gel, leading to the release of fluid and changes in the vitreous structure

Question 25

How does liquefaction lead to posterior vitreous detachment

Answer 25

Pockets of liquid coalesce leading to the gel shrinking As the vitreous contracts, vitreoretina adhesions are weakened, leading to vitreous pulling away from retina

Question 26

What percentage of people over 65years have PVD

Answer 26

About 70%

Question 27

What other comditions increases risk of PVD esp in younger age

Answer 27

High myopia Traumatic injuries eg retinal tear, vitreous haemorrhage

Question 28

What is the cause of most physiologic floaters

Answer 28

Small amounts of debris present in the vitreous, from the embryonic hyaloid vascular system

Question 29

Causes of other floaters

Answer 29

Collagen fibrils clumping together Vitreous hemorrhage Release of debris from infectious conditions eg uveitis

Question 30

What is the function of vitreous

Answer 30

Coordinating eye growth Protects eye during mechanical trauma Maintains eye shape Refractive properties

Question 31

Common complications of PVD

Answer 31

Retinal tears Macula hole Retinal detachment

Question 32

What are some causes of the perception of flashing lights

Answer 32

PVD Retinal traction/tears Retinal detachment

Question 33

What is the most abundant macromolecule in the vitreous

Answer 33

Hyaluronic acid