choroid

Question 1

what is the choroid?

Answer 1

the middle layer of eye in the posterior globe interior to it is the retina and external to it sclera

Question 2

how does the thickness of the choroid vary?

Answer 2

• thickness of choroid varies with location
  anteriorly near ora serrata = as little as 60um
  behind macular region = choroid is thick 160um

Question 3

how thick is the choroid in a myopic eye ?

Answer 3

myopic eye - the eye is elongated so coat is stretched making the choroid thin

Question 4

what are the three coats of the back of the eye?

Answer 4

• sclera - made of irregular dense collagen fibres
• choroid-
• retina-

Question 5

what separates the choroid and sclera?

Answer 5

suprachoroid- outer boundary of choroid

Question 6

what separates the choroid from the retina?

Answer 6

Bruch’s membrane

Question 7

what is between the suprachoroid and Bruch’s membrane?

Answer 7

3 layers of blood vessels

Question 8

what are the layers of the choroid?

Answer 8

1. suprachoroid
2. stroma - Haller’s layer
   - Sattler’s layer
3. choriocapillaris
4. Bruch’s membrane

Question 9

what is the choroid mainly made of ?

Answer 9

the choroid is mainly blood vessels

• blood vessels near the sclera are very large
• blood vessels near the retina are smaller

Question 10

what are the three layers of vessels in the choroid?

Answer 10

Haller’s layer - large which divide into
Sattler’s - medium
choriocapillaris - smaller

Question 11

what is suprachoroid

Answer 11

• also known as lamina suprachoroidea or lamina fusca
• composed of fine network of collagen fibres and between collagen fibres we have ciliary nerves running from front to back of eye which supply uveal tract
• also find some melanin granules
• a lot of nerves travel

Question 12

what is the whole layer of blood vessels know as ?

Answer 12

• choroidal stroma- which is split into Haller’s layer which is split into Sattler’s internal to that is choriocapillaris

Question 13

what does choroidal vessels constitute of ?

Answer 13

• choroidal vessels constitute a compressed hierarchy

- vessel branching occurs close together which produces a layered appearance

Question 14

what does bruch’s membrane separate ?

Answer 14

RPE - retinal pigment epithelium from choriocapillaris

Question 15

what is Bruch’s membrane made of ?

Answer 15

non-cellular connective tissue

Question 16

what are the layer of Bruch’s membrane? from external to internal

Answer 16

• basal lamina - secreted by choriocapillaris
• collagen - provided by choriocapillaris
• elastin
• collagen- provided by RPE
• basal lamina - secreted by RPE-

Question 17

what is the thickness of Bruch’s membrane?

Answer 17

2-6um

increases with age

Question 18

what does choriocapillaris supply?

Answer 18

• choriocapillaris supplies nutrients to the outer five layers of the retina

Question 19

what happens if Bruch’s membrane become thicker?

Answer 19

• the thickness of bruch’s membrane has some significance because if it gets thicker than the transport of nutrients from choriocapillaris into retina can become impaired
• causing Drusen

Question 20

what is Drusen?

Answer 20

common pathology - accumulation of debris in bruch’s membrane

• Drusen can push the retina away from Bruch’s membrane and away from choriocapillaris
• can impair flow of nutriebts

Question 21

what happens if Bruch’s membrane breaks?

Answer 21

• if it breaks you get local retinal edema - fluid gets through choriocapillaris and through the retina

Question 22

what is function of Bruch’s membrane?

Answer 22

• limits fluid movements towards the retina under normal conditions
• very important in retinal pathologies

Question 23

why is choriocapillaris important?

Answer 23

• provide nutrients to the outer five layers of the retina

Question 24

where the 5 inner layers of retina recveive blood supply from ?

Answer 24

• from the central retinal artery

Question 25

where do the 5 outer layers receive nutrients from ?

Answer 25

- they are devoid of blood vessels and receive their nutrients from the choriocapillaris

Question 26

what are unique characteristics of choriocapillaris ?

Answer 26

- large in diameter and fenestrated - fenestration 60-80 nm in diameter and covered by thin diaphragm - large fenestrations to allow the passage of substances such as vitamin A which is need to make visual pigments within the photoreceptors - fenestrations only occur on the retinal side of the capillary - the side facing Bruch's membrane

Question 27

what is main function of chorioid

Answer 27

through choriocapillaris to supply nutrients to 5 outer layers of retina

Question 28

why is blood flow high in the choroid?

Answer 28

- rate of blood in the choroid is very high - much higher than needed to supply the retina - may be due to thermoregulation function used to cool the outer retina during bright light exposure thus preventing damage

Question 29

what do we have between blood vessels in the choroid ?

Answer 29

- connective tissue components such as collagen fibres , plasma cells , mast cells and macrophages

Question 30

what other thing can be found in the choroid?§

Answer 30

- melanin granules in pigmented cells known as melanocytes

Question 31

what is the function of melanin in the choroid?

Answer 31

the melanin of the choroid along with that of ciliary body, iris and retina contributes to the eye's black box effect( light that isn't absorbed by photoreceptors) , serving to absorb stray light

Question 32

where does the eye's blood supply come from ?

Answer 32

the eye's blood supply comes from internal carotid artery, a branch off the aorta

Question 33

explain the eye's blood supply?

Answer 33

- when the left ventricle contracts it pushes the blood through the aorta - one of the first vessels that comes of the aorta is common carotid artery which takes blood up to head and neck - common carotid artery spilts into internal and external carotid

Question 34

what is the main vessel supplying the eye ?

Answer 34

- the main vessel supplying the eye is the ophthalmic artery, a branch of the internal carotid - branches off the ophthalmic artery supply various ocular structures - the globe is supplied by anterior and posterior ciliary arteries - anterior ciliary arteries pierce the globe anteriorly near the limbus - posterior ciliary arteries pierce the sclera near the optic nerve head. - short posterior ciliary arteries supply the choroid - long posterior ciliary arteries and supply the iris

Question 35

which arteries supply the choroid?

Answer 35

- short posterior ciliary arteries which come into back of eye supply the choroid

Question 36

which arteries supply the iris and ciliary body ?

Answer 36

long posterior ciliary arteries which come into the back of eye which run anteriorly and join anterior ciliary arteries and supply the iris and ciliary body

Question 37

where do anterior ciliary arteries and long posterior ciliary arteries join ?

Answer 37

- anterior ciliary arteries and the long posterior arteries join together at the base of the iris at the major iridic circle - in the major iridic circle you have vessels that go into iris into ciliary body and some recurrent branches which supply the anterior choroid