The Vitreous Humour

Question 1

Know the anatomy of the human vitreous

Answer 1

ok

Question 2

Give 4 physiological functions of the vitreous

Answer 2

-maintains transparency to visible light by excluding cells and large molecules
-cloquets canal for metabolic processes of the lens
-coordinates eye growth
-protects eye in mechanical trauma

Question 3

what are the 3 main parts of the vitreous

Answer 3

-central vitreous
-basal vitreous
-vitreous cortex

Question 4

where is the canal of clouquet in the vitreous?

Answer 4

In the central vitreous

Question 5

what is the fibril insertion in the central vitreous like and what’s its conc. compared to the basal and cortical vitreous

Answer 5

runs anteriorly into vitreous base and posteriorly into vitreous cortex

lower in conc. here than in basal and cortical vitreous

Question 6

what is the main GAG in the central vitreous?

Answer 6

hyaluronic acid

Question 7

how does the vitrous base extend?

Answer 7

1-2 mm anterior to ora serrata
3-4mm prosterior to ora serrata

Question 8

what part of the vitreous cortex is in direct contact with the aqueous?

Answer 8

the anterior vitreous cortex

Question 9

what chemicals make up the vitreous cortex?

Answer 9

hyalocytes, collagen, hyaluronic acid, chondroitin sulphate in higher concentration than in central vitreous

Question 10

how does the posterior vitreous sit on the retina?

Answer 10

-attached indirectly to inner limiting lamina of the retina
-adherent to retina
-absent at the optic disk
-thinned over the macula

Question 11

what is the vitreous composed of?

Answer 11

-hyalocytes in base and cortex, otherwise acellular
-98% water
-GAGs of hyaluronan
-unbranched collagen fibrils
-salts

Question 12

what are the three main vitreous properties?

Answer 12

-transparent
-non-compressible
-very viscoelastic: allows deformation with rapid restoration by acting as a shock absorber and slow diffusion of fluid

Question 13

what pathological condition are hyalocytes associated with?

Answer 13

proliferative vitreoretinopathy

Question 14

what go glycosaminoglycans GAGs bind with to form what?

Answer 14

proteins to form proteoglycans

Question 15

what three GAGs are found in the vitreous

Answer 15

hyaluronan
chondroitin sulphate
heparan sulphate

Question 16

Give 5 functions of hyaluronan

Answer 16

-forms space filling networks
-osmotic buffer
-molecular sieve excluding large molecules and cells
-lubricant
-forms viscoelastic solution that flows

Question 17

how does collagen conc vary in the vitreous?

Answer 17

-highest at the vitreous base
-decreases towards central and posterior
-increases at cortical

Question 18

what is the function of opticin in the vitreous?

Answer 18

prevents aggregation of collagen fibrils

Question 19

give 4 non collagenous structural proteins in the vitreous

Answer 19

-fibrillin
-opticin
-VIT1
-fibronectin

Question 20

what’s the significance of liquefaction and the vitreous?

Answer 20

liquid in the vitrious increases steadily with age and by age 80-90, >50% of vitreous is liquid

Question 21

give the mechanism of vitreous liquefaction

Answer 21

-initially occurs in pockets
-triggers like light, photosensitizers, fe ions cu ions and vitamin C cause reactive O2 species
-oxidation of proteins
-proteins cross-link
-appearance of collagen fibril aggregates
-‘floaters’
-hyaluronan polymers degraded
-leads to progressive loss of lattice structure
-re-distribution of collagen leaves areas devoid of collagen

Question 22

what can vitreous liquefaction be secondary to?

Answer 22

-inflammation
-infection
-tumour
-high myopia

Question 23

How does vitreous liquefaction lead to posterior vitreous detachment?

Answer 23

-pockets of liquid come together
-collagen fibres aggregate so conc of hyaluronic acid is the same
-adhesion at vitreoretinal interface weakens
-PVD

Question 24

what is the most probable cause of flashes

Answer 24

stimulation of the retina by vitreoretinal traction

Question 25

what can posterior vitreous detachment protect against and how?

Answer 25

proliferative diabetic vitreoretinopathy by removing the substrate that would otherwise allow vessels to grow into cortical vitreous gel which would lead to haemorrhage, fibrosis and retinal detachment.

Question 26

give some therapeutic interventions of PVD

Answer 26

surgical vitrectomy and pharmacological vitriolises

Question 27

which part of the vitreous contains the smallest density of hyalocytes?

Answer 27

the central vitreous

Question 28

What is the most abundant macromolecule in the vitreous?

Answer 28

hyaluronan

Question 29

what is the main component in the human vitreous

Answer 29

water