choroid Flashcards
what is the choroid?
the middle layer of eye in the posterior globe interior to it is the retina and external to it sclera
how does the thickness of the choroid vary?
- thickness of choroid varies with location
anteriorly near ora serrata = as little as 60um
behind macular region = choroid is thick 160um
how thick is the choroid in a myopic eye ?
myopic eye - the eye is elongated so coat is stretched making the choroid thin
what are the three coats of the back of the eye?
- sclera - made of irregular dense collagen fibres
- choroid-
- retina-
what separates the choroid and sclera?
suprachoroid- outer boundary of choroid
what separates the choroid from the retina?
Bruch’s membrane
what is between the suprachoroid and Bruch’s membrane?
3 layers of blood vessels
what are the layers of the choroid?
- suprachoroid
- stroma - Haller’s layer
- Sattler’s layer - choriocapillaris
- Bruch’s membrane
what is the choroid mainly made of ?
the choroid is mainly blood vessels
- blood vessels near the sclera are very large
- blood vessels near the retina are smaller
what are the three layers of vessels in the choroid?
Haller’s layer - large which divide into
Sattler’s - medium
choriocapillaris - smaller
what is suprachoroid
- 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
what is the whole layer of blood vessels know as ?
- choroidal stroma- which is split into Haller’s layer which is split into Sattler’s internal to that is choriocapillaris
what does choroidal vessels constitute of ?
- choroidal vessels constitute a compressed hierarchy
- vessel branching occurs close together which produces a layered appearance
what does bruch’s membrane separate ?
RPE - retinal pigment epithelium from choriocapillaris
what is Bruch’s membrane made of ?
non-cellular connective tissue
what are the layer of Bruch’s membrane? from external to internal
- basal lamina - secreted by choriocapillaris
- collagen - provided by choriocapillaris
- elastin
- collagen- provided by RPE
- basal lamina - secreted by RPE-
what is the thickness of Bruch’s membrane?
2-6um
increases with age
what does choriocapillaris supply?
- choriocapillaris supplies nutrients to the outer five layers of the retina
what happens if Bruch’s membrane become thicker?
- 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
what is Drusen?
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
what happens if Bruch’s membrane breaks?
- if it breaks you get local retinal edema - fluid gets through choriocapillaris and through the retina
what is function of Bruch’s membrane?
- limits fluid movements towards the retina under normal conditions
- very important in retinal pathologies
why is choriocapillaris important?
- provide nutrients to the outer five layers of the retina
where the 5 inner layers of retina recveive blood supply from ?
- from the central retinal artery
where do the 5 outer layers receive nutrients from ?
- they are devoid of blood vessels and receive their nutrients from the choriocapillaris
what are unique characteristics of choriocapillaris ?
- 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
what is main function of chorioid
through choriocapillaris to supply nutrients to 5 outer layers of retina
why is blood flow high in the choroid?
- 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
what do we have between blood vessels in the choroid ?
- connective tissue components such as collagen fibres , plasma cells , mast cells and macrophages
what other thing can be found in the choroid?§
- melanin granules in pigmented cells known as melanocytes
what is the function of melanin in the choroid?
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
where does the eye’s blood supply come from ?
the eye’s blood supply comes from internal carotid artery, a branch off the aorta
explain the eye’s blood supply?
- 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
what is the main vessel supplying the eye ?
- 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
which arteries supply the choroid?
- short posterior ciliary arteries which come into back of eye supply the choroid
which arteries supply the iris and ciliary body ?
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
where do anterior ciliary arteries and long posterior ciliary arteries join ?
- 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
