Choroid and vitreous

Question 1

What connects the lamina fusca (innermost scleral layer) to the choroid?

Answer 1

Fine collagen fibres- weak attachment

Potential space between choroid and lamina fusca =perichoroidal space

Question 2

What runs within the perichoroidal space?

Answer 2

Long and short posterior ciliary arteries and nerves

Question 3

Where does the choroid become continuous with the pia and arachnoid?

Answer 3

At optic nerve

Question 4

What are the 3 layers of the choroid?

Answer 4

Suprachoroidea/lamina fusca
Vessel layer(Sattlers and Hallers)
Capillary layer/ Choriocapillaries
Bruch’s membrane (acellular)

Question 5

What are the 5 layers of Bruch’s membrane?

Answer 5

2-4 microns thick (thickest near disc)
BM of endothelium of capillaries
Outer layer of collagen fibres
Elastic fibre layer
Inner layer of collagen fibres
BM of pigment epithelium of retina

Question 6

Where does the choroid run from?

Answer 6

Ora serrata anteriorly
Optic nerve posteriorly
Internally: RPE
Externally: Lamina fusca

Question 7

What is the function of choroid?

Answer 7

Nourish outer layers of retina
Conduct blood vessels. nerves to anterior uvea
Thermoregulation
Absorbs excess light to prevent reflection (melanocytes within the choroidal stroma)

Question 8

What is thickness of choroid?

Answer 8

Thickest at posterior pole 0.22mm

0.1mm at equator

Question 9

What is the arterial supply of choroid?

Answer 9

Mainly long and short posterior ciliary arteries
Long from equator to orra serrata (anterior choroid)
Short from optic nerve to equator

Recurrent branches from anterior ciliary arteries

Question 10

Describe the uveal vessels

Answer 10

Supply whole eye except neurosensory retina
Comes from ophthalmic artery
Becomes medial and lateral posterior ciliary arteries which divide into 10-20 branches
Most become short posterior ciliary arteries
2 become long posterior ciliary arteries
Some short posterior ciliary arteries anastomose around the optic nerve to form Circle of Zinn-Haller

Question 11

Where do the long posterior ciliary arteries run?

Answer 11

Enter along horizontal meridian
Run anteriorly between sclera and choroid to ciliary body
Sends branches to ora serrata to supply anterior choroid up to equator
Also supplies iris, anterior part of ciliary body and ciliary processes

Question 12

Where do the short posterior ciliary arteries run?

Answer 12

Run forward with optic nerve
Most enter globe temporally to optic nerve
Run in Haller’s layer of the choroid
Supply posterior choroid up to equator
Medial branches form Circle of Zinn/Haller to supply optic nerve head

Question 13

Where do the anterior ciliary arteries run?

Answer 13

Run with recti (2 for each rectus except LR which only has 1)
Contribute to main arterial circle of iris
Contributes small amounts to supply choroid

Question 14

What is the venous drainage of the choroid?

Answer 14

Number of vortex veins variable
2 inferior vortex veins which drain into inferior ophthalmic vein
Exit the globe at equator via posterior sclera
2 superior vortex veins -> superior ophthalmic vein
Ophthalmic veins drain into cavernous sinus

Question 15

Where do drusen lie?

Answer 15

Between the retinal pigment epithelium and Bruch’s membrane

Question 16

Describe the choriocapillaris/capillary layer of choroid

Answer 16

Continous vascular sheet that lies beneath Bruch’s membrane
A lobular structure
Architecture of the layer varies from area to area
Largest capillaries in the body

Question 17

Describe the different variations in the choriocapillaris

Answer 17

Prepapillary/submacular regions: Honeycomb
Posterior pole equator: lobular with central postcapillary venules and precapillary arterioles
Peripheral region: Elongated

Question 18

Describe the capillaries of the choriocapillaris

Answer 18

Fenestrated-more fenestrated on Bruch's membrane side
Wide lumen
Meshwork spaces vary
1. posterior-small +oval
2. equator- long+wide
3. peripheral-irregular

Question 19

What gets more blood, the choroid or retina?

Answer 19

Choroid blood flow 20x that of retinal blood flow
Exceeds nutritional deman
May play thermoregulatory role and buffer for rises in IOP

Question 20

What are the two layers of the stroma/vessel layer of choroid?

Answer 20

Hallers: outer-large arterioles
Sattlers: deeper- intermediate arterioles

Question 21

Why is infarction of the choroid uncommon?

Answer 21

Extensive anastomosis between vessels

Question 22

Which nerves run in the stroma of the choroid?

Answer 22

20 short posterior ciliary nerves from ciliary ganglion
2 long posterior ciliary nerves from nasociliary nerve V1

Nerves branch at ora serrata

Question 23

Which layer of the choroid contains melanocytes?

Answer 23

vessel/stroma layer

Lamina fusca

Question 24

Why are suprachoroidal infusions usually anterior to the equator?

Answer 24

Collagen lamellae packing in lamina fusca is not as compact anteriorly

Question 25

What is the embryological origin of the choroid?

Answer 25

MESENCHYMAL

Question 26

When during gestation is the choroidal vasculature developed?

Answer 26

6th week- choriocapillary network has basal lamina and vortex veins develop 11th week posterior ciliary arteries have branches throughout the choroid 3rd-4th month-choroidal vasculature is mature

Question 27

What is the definition of the vitreous?

Answer 27

``` Transparent gel, fills posterior globe Roughly spherical with anterior concavity 4ml 4g 99% water Denser at surface Viscosity is 2x H2O (varies with age) ```

Question 28

Describe the embryology of the vitreous

Answer 28

ECTODERM +NEUROECTODERM +MESENCHYMAL 3 stages 4-5 weeks-Primary: network of cytoplasmic proteins between lens and optic cup derived partly from ectoderm (developing lens) and neuroectoderm (retinal layer of optic cup)-vascular supply hyaloid artery Secondary: between primary vitreous and retina. Homogenous gel that pushes primary vitreous anteriorly. Basically ECM made of type 2 collagen+hyalocytes- avascular 3-4 months-Tertiary: large numbers of collagen fibres develop with formation of zonular fibres

Question 29

What are the relations of the vitreous?

Answer 29

Anteriorly: ciliary body, lens and zonules Posteriorly: retina

Question 30

What is the patella fossa?

Answer 30

Anterior concavity in vitreous to accomodate lens | Separated from the lens by a potential space (Space of Berger)

Question 31

What is the ligamentum hyaloideocapsure of Wieger?

Answer 31

Circular lining of vitreous delineating the patella fossa Adherent to lens capsule but weakens with age Adherent to hyaloid zonule

Question 32

What is the anterior hyaloid surface?

Answer 32

Cortex of vitreous anterior to the ora serrata | Can be seen on slight lamp

Question 33

What is the vitreous base?

Answer 33

Denser cortex attached to the posterior 2mm of pars plana and anterior 4mm of retina Often site of retinal tears

Question 34

What is the posterior hyaloid surface?

Answer 34

Cortex of vitrous posterior to ora serrata Opposed to Internal limiting membrane Firm adhesions to vessels

Question 35

What is cloquet's canal?

Answer 35

S- shaped canal within vitreous from space of Berger to space of Martegioni Represents the site of the primary vitreous and hyaloid artery

Question 36

How does the vitreous change with age?

Answer 36

Birth: homogenous Infancy: cortex develops anteriorly. Central vitreous decreases in density Adolescence: Vitreous tracts form anteriorly Adult: Vitreous tracts reach posterior vitreous Elderly: central vitreous liquifies and tracts are gradually broken down

Question 37

Why does posterior vitreous detachment occur?

Answer 37

The liquid central vitreous enters subhyaloid space and acts like a wedge with inertia to strip vitreous cortex off retina with each eye movement

Question 38

Which microscopic structures make up the vitreous?

Answer 38

Vitreous cells Vitreous cortex (anterior hyaloid, vitreous base, posterior hyaloid, peripapillary and macular attachments) Central vitreous

Question 39

What makes up the vitreous cortex?

Answer 39

Dense zone enveloping vitreous Inserts anteriorly onto basal lamina of ciliary epithelium and posteriorly onto ILM of retina Made up of hyaluronic acid, GAGs and type 2 collagen Basal lamina is 20-100nm thick Thickens posteriorly and with age Acts as a barrier to large molecules Interrupted at pars plana/ciliary

Question 40

What is the premacular cortex?

Answer 40

May become apparent with abnormal vitreoretinal adhesions

Question 41

What is the prepapillary cortex?

Answer 41

1micro wide circular zone at dic margin where Muller cells end and optic nerve glia start

Question 42

How does the central vitreous differ form the cortex?

Answer 42

Similar to cortex but less cells/collagen GAGs separate collagen to maintain transparency In elderly breakdown means collagen forms coarse strands (visible clinically) Acellular

Question 43

Which cells are present in the vitreous?

Answer 43

Found in vitreous cortex Phagocytic cells called hyalocytes which make hyaluronic acid Increase in number with inflammation A few fibrocytes and glial cells

Question 44

What is the composition of the vitreous

Answer 44

``` Mostly water Hyaluronic acid(HMW proteoglycan->highly viscous) Fine fibrillar collagen type II ```

Question 45

What is the neurovasculature of the vitreous?

Answer 45

Not physiologically present May have persistent hyaloid artery Neovascularisation may occur secondary to retinal ischaemia

Question 46

When does the hyaloid artery regress?

Answer 46

Tunica vasculosa lentis and hyaloid artery regress at the end of the 3rd month, leading to retraction of primary vitreous and secondary avascular vitreous develops. By month 7, blood flow in hyaloid has ceased