Lecture 18/19 Flashcards
What are the three circulatory systems serving the retina?
- central retinal circulation
- choroidal circulation
- optic nerve head circulation
the central retinal artery enters the optic nerve how far behind the globe? what does it supply?
12 mm
optic nerve and pia mater
what surrounds the central retinal artery? once in the eye the CRA branches into what?
sympathetic nerve plexus (or nerve of tiedemann)
superior, inferior, nasal and temporal branches
central retinal circulation supplies what and is made up of?
inner retina (ganglion and bipolar cells) made up of central retinal artery and veins (in nerve fibre layer), capillary system (double layered system in most of outer retina) and radial peripapillary circulation.
CRC has what major concepts?
sparse and thin to allow light to reach PR layer, high resistance. slow supply of blood with virtually all the oxygen extracted.
the radial peripapillary circulation follows which arteries? stops wherE?
superior and inferior temporal arteries, stops short of macula
what is the only blood supply to the macula?
choroid.
choroidal circulation supplies what? what type of capillaries?
outermost layers, photoreceptors and RPE (lies posterior to RPE, HUGE blood supply)
fenestrated
what are the three arteries involved in CC?
- short posterior ciliary arteries (further branches into paraoptic (near optic nerve head, supplies ONH and choroid)) and distal (further from optic nerve head, branches further once in choroid))
- LPCA: one lateral, one medial (sometimes one superior)
- Cilioretinal artery (small supply to retina, 25% of population)
how many SPCA?
8-10
distal SPCA branch into how many more? each branch supplies what? what do terminal arterioles supply (the ones at the end of the smaller branches from distal SPCA)?
10-12 (within each branch, smaller branches supply smaller segments)
a sector of the choroid
a lobule
two anterior ciliary arteries arise from each of what? what is the exception?
rectus muscles
lateral rectus only gives rise to one
what is the amount of oxygen located in the CC compared to CRC?
much more in CC (excess reserve)
cilioretinal arteries originate from what?
SPCA
how many LPCA?
usually two, can be up to five.
do medial and lateral LPCA supply the same thing?
both supply small sector of ciliary body and iris. lateral will supply the peripheral choroid that is not reached by the medial LPCA.
what is a watershed zone?
border between the territories of distribution of any two end arteries, poor vasculairty and most vulnerable to ischaemia (inadequate blood supply)
the choriopcapillaris is divided into? if one lobule is destroyed are all the others? does the central lobule have its own blood supply? does the macula receive any blood supply from the CRC?
lobules
NO
NO (gets from others around it)
NO ONLY CC
where are watershed zones located?
medial and lateral LPCA
segments supplied by SPCA
SPCA and LPCA
Are all watershed zones the same?
NO, major individual variation
what is a choroidal occlusion? what is a pro about this?
loss of a lobule (happens very fast and can be irreversible within hours/days)
only affects a very small area therefore not a HUGE issue
cilioretinal arteries act as a alternative blood supply for? is it sufficient? are these arteries a good thing?
central retinal artery (for retina), NOT sufficient to supply retina on its own.
not always, they tend to bleed more often.
optic nerve head circulation is comprised of? this circulation is implicated in which two disease groups?
paraoptic short posterior ciliary arteries and CRA.
glaucoma and ischemic optic neuropathy (loss of blood flow to ONH)
circle of zinn haller is made up of anastomoses between which three circulatory systems?
- CRC
- choroidal circulation
- optic nerve head circulation
what are the four parts of the ONH circulation?
- superficial nerve fibre layer (most superficial)
- pre lamina
- lamina
- retrolamina (most deep)
what are the six possible hemorrhages and where are they usually found?
- dot and blot (bipolar cell layer)
- flame shaped (superficial layer)
- pre retinal (before the retina, into vitreous)
- Boat (between retina and vitreous)
- sub-retinal (beneath retina)
- choroidal (choroid layer)
what is coats disease?
abnormal development in blood vessels behind the retina. seen mostly in males (69% of cases are males). almost always unilateral. pupil can appear yellow due to RPE leaking fluid (serum) into retina.
CRA occlusion can cause what symptoms? is the macula affected?
- ganglion cell death
- cotton wool spots (liquid accumulation)
- no oxygen or glucose reserves
- immediate VA drop, fast, painless, acute
NO because not supplied by CRA therefore it is bright red and rest of retina is pale.
CRV occlusion causes what?
blockage of outflow
increase in transmural pressure (therefore blood pushed into retina)
blood and thunder retina
BP very high therefore vessels increasing in size
VA may not be affected
what is poiseuilles law? what pressure drives blood through a capillary bed? a decrease in perfusion pressure leads to an increase in?
blood flow in a vessel occurs if there is a pressure gradient between two points.
perfusion pressure
transmural pressure therefore decreasing blood flow and initiating autoregulation.
blood flow is autoregulated when?
there is an increase in blood pressure
what do we mean by autoregulation?
the ability to regulate blood flow and maintain available O2 at a constant level.
increase in transmural pressure leads to?
decrease in perfusion pressure, produces vasodilation, reduces resistance to flow, increases perfusion pressure.
changes in vessel diameter are due to? defective autoregulation leads to? what is the transmural pressure in veins?
changes in blood pressure or IOP.
isechemic damage
zero (due to IOP and venous pressure being relatively the same)
what systems use autoregulation?
central retinal circulation
capillaries in superficial nerve fibre layer in ONH
blood vessels in pre laminar layer in ONH
NOT CC
what receptors play a role in blood pressure detection?
baroreceptors in carotid sinus play a major role.
blood flow begins to fall at?
60cm water/40mmHg
arteries have what kind of transmural pressure? veins?
HIGH (TMP=Ta-IOP)
LOW (TMP=Tv-IOP, usually around 0)
the venous pulse was thought to disappear when?
IOP is too high or venous pressure is too low.
SVPs are present in how many of normal subjects? not present in how many normal subjects? it occurs only in people with a CSF pressure below what? when IOP=CSF pressure what happens?
90%
10%
190mmHg
there is no pulse
does normal IOP mean that CSF pressure is normal?
not necessarily
what are the three type of open angle glaucoma?
- low tension
- primary open angle
- ocular hypertension