Trabecular meshwork and aqueous outflow Flashcards
AC mean depth is? horizontal diameter of AC? Vertical diameter was?
3.64mm
12.20mm
vertical larger than horizontal by about 100 um
aqueous humor fills what part of the eye? supports metabolic needs of avascular tissues such as?
anterior segment (clear nutritive fluid) lens, cornea and TM
aqueous humor is secreted by what? at what rate?
ciliary body at a rate of 2.5ul per min. amount produced must equal amount drained.
pathway of aqueous humor from schawlbes line to ciliary body band?
schawlbes line (where decemets ends and TM starts) -> schlemms canal ->TM ->sceral spur (posterior region of TM) ->ciliary body band
What is the conventional outflow pathway of aqueous humor starting with aqueous humor and ending with venous system?
aqueous humor, uveal meshwork, corneoscleral meshwork (anterior TM), juxtacanalicular meshwork (JCT), schlemms canal, collector channels, deep scleral plexus, intrascleral plexus, episcleral veins and then venous system.
in the aqueous outflow pathway what two types of regions are there?
non filtering (anterior) and filtering (posterior, lots of pigment here compared to anterior).
the five layers found in a normal open angle in goniophotograph view are?
- schawlbes line
2/3. two layers of TM - scleral spur
- ciliary body band
scleral spur is a point of attachment for which muscles?
longitudinal bundle of CM
schawlbes line is a peripheral terminus of which corneal layer?
decemets.
what percent of aqueous humor flows out through TM path? what does other percent do?
80% out of TM path
other 20% goes through uveal path or non conventional
What is the issue with the spacing between the uveal meshwork and cornealscleral meshwork? however as we get closer to what, what happens?
interlamellar spaces are too large to generate significant resistance.
as we get closer to schlemms canal, spacing becomes smaller therefore generating resistance.
Principle pressure drop is what and occurs where? therefore, this indicates that the most probable location of the majority of outflow resistance in the normal eye is where?
7-14um of inner wall of schlemms canal.
JCT region and/or inner wall of schlemms canal.
when the CM contracts, what does this cause?
opening of TM and schlemms canal to allow outflow.
On the inner wall endothelial cells of schlemms canal what are two unique aspects?
giant vacoules (outpouchings) and pores. there are two types of pores which are intracellular (I pores) and paracellular or border pores (B pores)
the giant vacoules in the inner wall of schlemms can form how? these vacoules are dependent on what?
by one cell or two cells fusing together.
pressure (not found unless inner wall is fixed under conditions of flow).
How does the aqueous humor pass through the inner wall of schlemms?
JCT, giant vacoule, pore then canal.
In the inner wall of schlemms, where are b pores found? i pores?
B pores always found between two cells
I pores found in just one cell.
In glaucoma, how does this affect the number of pores found in inner wall of schlemms?
in glaucoma, we see that the pores are reduced allowing for pressure build up.
is aqueous outflow uniform?
NO, only a fraction of JCT TM and inner wall of schlemms are active in filtration at any given time.
normal pressure in an anucleate eye? what was found with increasing IOP?
7mmHg
schelmms canal became narrower, JCT and inner wall were pushed into collector channels therefore confining flow to a smaller area.
how many collector channels per eye? where and how are they distributed?
+/- 30
unevenly distrbuted throughout schlemms.
which TM is closest to AC?
uveal TM
in closed angle glaucoma what happens? what happens in open angle? what happens in pseudoexfoliation glaucoma?
iris and cornea attach to each other
structure in TM is blocked therefore aqueous humor cant get out of the eye.
PEX material accumulates under JCT
What happens in pigmentary glaucoma?
pigment liberated from the iris clogs the TM and impedes aqueous outflow.
intraocular pressure plays a major role in maintaining what in the eye?
shape and function.
normal IOP? what is classified as hypertension?
15mmHg
> 21mmHg
glaucoma can cause what kind of damage? can be noticed in back of eye due to? which vision is lost in glaucoma?
nerve (due to high pressure)
big cup around optic disk.
peripheral visual field loss.
once aqueous humor is produced by ciliary processes of ciliary body, where is it secreted?
posterior chamber
what is the uveoscleral pathway (non conventional)?
ciliary muscle, across sclera, along supraciliary and suprachoroidal spaces, emissarial vanals, choroidal vessels, vortex veins and into ciliary processes where it is secreted again.
what is the only source of aqueous production?
ciliary body
when CM contracts what happens?
scleral spur is pulled back, TM opens up and schlemms canal, facilitating outflow.
how many pars plicata? they are divided into what?
70-80. major processes (1mm) and minor processes (1/3 that of major)
how does pars plana differ from pars plicata?
it is a thinner layer, flat and is less vascularized therefore making it the safest point of entry for surgical procedures.
what type of layer surrounds CB?
bilayered epithelium. pigmented and non pigmented layers.
the pigmented epithelium of the iris becomes what in the CB? the non pigmented or myoepithelium of the iris becomes what in CB?
non pigmented ciliary epithelium
pigmented ciliary epithelium
non pigmented ciliary epithelium becomes what? pigmented ciliary epithelium becomes what?
neural retina
RPE
the bilayered epithelium in the iris and CB are in what structural formation? the two layers of epithelium are derived from what?
apex to apex
neuroectoderm of optic vesicle that invaginates on itself during emrbyogenesis.
aqueous humor is derived from what? this happens where? filtrate is converted to aqueous humor where?
plasma filtrate
in ciliary body microvasculature.
ciliary epitheium ( in CB).
the ciliary body microvasculature is made up of what two things?
- anterior ciliary aterioles: provide fenestrated capillaries to ciliary processes, this is the blood supply for aqueous humor
- posterior arterioles: not as deep as anterior, serves the ciliary muscle with non fenestrated capillaries.
capillaries of CB stroma are fenestrated or non? therefore allows?
fenestrated (and lacks tight junctions)
therefore very permeabe
what are three major factors that determine the amount of plasma filtrate available in ciliary body for aqueous production?
- hydrostatic pressure: in capillaries of ciliary processes, drives ions, fluid and small molecules of plasma filtrate
- intersitial fluid pressure: increases with increases IOP, counteracts hydrostatic pressure
- elevations of IOP give rise to reductions in aqueous inflow and after a delay, decrease in IOP.
what exists between the CB stroma and posterior chamber? is there a barrier between stroma and anterior chamber?
selective permeability barrier= blood aqueous barrier.
NO, very permeable.
Are iris capillaries fenestrated?
NON fenestrated, has tight junctions between cells.
are there tight junctions present between the non pigmented ciliary epithelium cells?
YES
which ions are used from plasma filtrate for aqueous humor production?
sodium, bicarbonate and chloride.
which two pumps have been found to be involved in formation of aqueous humor by the non pigmented ciliary epithelium?
na+/K+ Atpase and carbonic anhydrase activity
it was originally thought that the % of protein in AC and PC was what? now what do we believe? more protein in aqueous humor than normal suggests what?
equal. now they differ, they think there is now more in AC than PC (almost zero in PC compared to about 1% in AC)
broken tight junctions.
What prevents plasma protein diffusion between the anterior and posterior chambers?
tight junctions in the iris.
a rise in aqueous humor protein concentration is called what? usually due to? what are two examples that are NOT due to the normal cause of flare?
a flare (usually due to tight junction breakdown)
timolol: reduced aqueous production, gives flare
pilocarpine: constricts pupils due to thinning of iris, gives flare
which endothelial cells are fenestrated and lack tight junctions?
capillaries of ciliary stroma
what are the three sets of ciliary muscles? most inner muscle is? outer?
longitudinal, radial and circular.
inner= circular
outer=longitudinal
during accommodation do zonules relax or contract?
relax causing an increase in lens power myopic.
ciliary body facilitates aqueous outflow by contracting which of the three CB muscles?
longitudinal.
big difference between TM outflow and uvealsceral? if there is a blockage of TM outflow will there be an increase in uveo flow?
uveo scleral is NOT pressure dependent, TM is.
YES
prostaglandin F2 alpha was found to do what?
increase uveo scleral outflow by decreasing the extracellular matrix between ciliary muscle bundles.
whata re three principle functions of CB?
- produces/secretes aqueous humor into PC
- contains smooth muscle that acts upon lens via zonule fibres to shift focus of eye from far to near
- can assist in drainage of aqueous humor from eye.
