Vitreous Humor

Question 2

how much of the eye is vitreous humor

Answer 2

80% (largest structure)

Question 3

how long is the vitreous chamber in newborns

Answer 3

10.5mm

Question 4

how long is the vitreous chamber in adults

Answer 4

16.5mm

Question 5

how much of the vitreous is water

Answer 5

about 98%

Question 6

what are the non-aqueous biochemical components of the vitreous

Answer 6

collagen and glycosaminoglycans (GAGs) that form the vitreous into a viscoelastic gel

Question 7

when does the vitreous gel become liquified

Answer 7

it decreases with age-starting the day we are born, 20% (volume) by age 18 and progresses to 50% by 80th decade

Question 8

what are the 2 types of collagen in the vitreous

Answer 8

type 2 (75%) and combined type 5/11 (10%)

Question 9

what are 2 difficulties that arise in attempting to investigate the vitreous

Answer 9

it is “invisible” tissue and previous techniques are combined with artifacts, it is hard to make interpretations on the true in vivo situation

Question 10

how is the primary vitreous formed

Answer 10

the optic cup is maintained by the lens vesicle, as the cup grows it is filled by fibrillar material (secreted by cells of embryonic retina), then the hyaloid artery penetrates and more fibrillar material from blood vessel cells fills the space

Question 11

when does the secondary vitreous form

Answer 11

at the end of the 6th week

Question 12

what happens as the secondary vitreous is formed

Answer 12

the size of the vitreous cavity increases and the hyaloid vascular system regresses

Question 13

what is present after the hyaloid artery regresses

Answer 13

a tube in the primary vitreous surrounded by the secondary vitreous- Cloquet’s canal

Question 14

where does cloquet’s canal extend to and from

Answer 14

from the retrolental space to the optic nerve

Question 15

what type of vitreous are the zonules

Answer 15

tertiary vitreous

Question 16

what shape does the mature vitreous have

Answer 16

spherical except anteriorly which is concave shape for the lens

Question 17

What does the vitreous base extend from

Answer 17

a 3-D zone extending from 2mm anterior to 3mm posterior to the ora serrata and it is several mm thick

Question 18

what is the cortex

Answer 18

the outermost part of the vitreous; divided into anterior cortex and posterior cortex

Question 19

where in the vitreous is collagen densely packed

Answer 19

in the base area

Question 20

what is the vitreoretinal interface

Answer 20

the outer part of the vitreous cortex, including anchoring fibrils of the vitreous body and the internal limiting membrane of the retina

Question 21

how thick is the internal limiting membrane on the retina

Answer 21

between 1 and 3 microns thick

Question 22

where are the 4 places the vitreous cortex is firmly attached to the internal limiting membrane at

Answer 22

the vitreous base, around the optic disc (weiss ring), at the vessels and in the area surrounding the foveola

Question 23

the INM (internal limiting membrane) is the basal lamina of which cells

Answer 23

the muller cells

Question 24

what is the internal limiting membrane made of

Answer 24

mainly type 4 collagen and proteoglycans

Question 25

what does the gel structure of the vitreous act as a barrier against

Answer 25

the movement of solutes

Question 26

what are the two processes substances move by in the vitreous

Answer 26

diffusion or bulk flow

Question 27

why does bulk flow occur in the vitreous

Answer 27

it is a result of a pressure gradient from the anterior to posterior pole of the eye

Question 28

is bulk flow a significant way to distribute low molecular weight substances in the vitreous

Answer 28

no

Question 29

what type of molecules move with bulk flow

Answer 29

large, high molecular weight substances

Question 30

what disolves and replaces the gel structure

Answer 30

aqueous lacunae: small pockets of liquid (melt together over time and creates a detachment)

Question 31

why does the apparent molecular weight of vitreous collagen increase with age

Answer 31

because of the formation of new covalent cross-links between the peptide chains

Question 32

what are the 4 main aspects of vitreous physiology

Answer 32

1. support function for the retina and filling-up function of the vitreous cavity 2. diffusion barrier between the anterior and posterior segments 3. metabolic buffer function 4. establishment of an unhindered path of light

Question 33

what is the Maillard reaction

Answer 33

insoluble proteins produced by a covalent bond between an amino group and glucose (why proteins are cross-linked)

Question 34

how does the vitreous support the retina

Answer 34

helps prevent a large retinal detachment and absorb external forces to protect globe deformation

Question 35

how much is the concentration of glucose increased in the vitreous of diabetic patients

Answer 35

it is doubled in concentration

Question 36

what is a PVD

Answer 36

posterior vitreous detachment: central degeneration is large and causes a collapse --> the cortex sinks to the center of the vitreous body

Question 37

when can a PVD result in a retinal tear

Answer 37

if there is a strong attachment between the posterior cortex and the internal limiting membrane and the vitreous pulls the retina away from that spot

Question 38

who is most likely to get a PVD

Answer 38

it is considered a common pathophysiologic condition (normal aging phenomena)

Question 39

what is the first step in a rhegamatogenous retinal detachment

Answer 39

a PVD (RRD is the worst type of retinal detachment- fluid accumulates between the neurosensary retina and the RPE)

Question 40

in untreatable edema, will performing a vitrectomy improve VA's

Answer 40

yes and it will decrease the edema

Question 41

what causes macular edema

Answer 41

increased passive permeability and decreased outward active transport (normally the blood-retinal barrier is tight- low passive permeability)

Question 42

how is the vitreous a diffusion barrier between anterior and posterior segments

Answer 42

diffusion is slow and movement by bulk flow is limited in a gel (also preventing topical substances from reaching the retina and optic nerve)

Question 43

what happens to the barrier after removal of lens and anterior vitrectomy

Answer 43

the exchange between the anterior and posterior is fast and easy

Question 44

what happens in diabetic patients (who don't have bleeding) after a vitrectomy

Answer 44

the pre-retinal oxygen tension is improved- oxygen transport increases and retinal neovascularization and macular edema regress

Question 45

how can the vitreous act as a metabolic buffer

Answer 45

it can be a reservoir for metabolism of the ciliary body and retina

Question 46

what do the glucose and glycogen reserves in the vitreous supplement

Answer 46

the metabolism of the retina especially during anoxic conditions

Question 47

can a vitrectomy stop or cure diabetic retinopathy if there is active blood leaking

Answer 47

no it can lead to rapid movement of vasoproliferative factors from the posterior pole to the anterior pole- leading to neovascularization of the anterior segment (neovascular glaucoma)

Question 48

what does the vitamin C reserve in the vitreous supplement

Answer 48

it acts as a reservoir of antioxidants for stress situations protecting the retina from metabolic and light induced free radicals

Question 49

why is light unhindered in the vitreous

Answer 49

it produces a low concentration of structural macromolecules

Question 50

what are 6 pathological conditions that interfere with transparency of the vitreous

Answer 50

synchysis scintillations, asteroid degeneration, hemorrhages, inflammatory material, fibrous tissue, and lack of regression of the hyaloid artery

Question 51

what is a vitreo-macular traction

Answer 51

where the vitreous is lifting away from the retina and pulling on the fovea (seen with an OCT)- patients are unaware/no symptoms