Aqueous Humor

scleral spur, trabecular meshwork, juxtacanalicular tissue, canal of Schlemm

what are the 4 structures of the anterior chamber angle?

scleral spur

• located at posterior edge of internal scleral sulcus

• posterior portion is attachment site for tendon of longitudinal ciliary muscle fibers

• anterior portion is attachment site for trabecular meshwork sheets

collagen of trabeculae

collagen of the scleral spur is continuous with the ______

trabecular meshwork

• encircles the circumference of the anterior chamber, occupying most of the inner aspect of internal scleral sulcus

• triangular shape in cross-section

• flattened, perforated sheets

• inner face borders anterior chamber

• outer side lies against corneal stroma, sclera, and Schlemm’s canal

• C

Descemet’s membrane

what structure is the apex termination of the trabecular meshwork?

scleral spur

what structure is the base termination of the trabecular meshwork?

3-5

how many sheets of trabecular meshwork are at the apex?

15-20

how many sheets of trabecular meshwork do the apex sheets branch into?

open latticework

the trabecular meshwork is described as being what?

spaces of Fontana

historic name for the openings within trabecular meshwork sheets

smaller

openings in trabecular meshwork sheets become _____ as it nears Schlemm’s canal

no

are there any apertures that directly join the meshwork with the canal of Schlemm?

corneoscleral meshwork

• outer region of the trabecular meshwork

• sheets attach to the scleral spur

• sheetlike

uveal meshwork

• inner sheets of trabecular meshwork

• inner to the spur and attach ciliary stroma and longitudinal muscle fibers

• may attach to iris root

• cordlike

• largest pores

iris processes

projections from surface layer of the iris that connect to the trabeculae

inner core of collagen & elastic fibers

the meshwork trabeculae is described as ________________________ embedded in ground substance

basement membrane and endothelium

the trabecular meshwork is covered in what?

corneal endothelium

the endothelial cells of the trabecular meshwork are a continuation of what?

connective tissue components

what are the endothelial cells of the trabecular meshwork capable of replacing?

lysosomes

trabecular meshwork endothelial cells contain what to enable phagocytosis?

gap junctions

what sort of intercellular junction is found in the trabecular meshwork endothelial cells?

no

are any zonula occludens found in the trabecular meshwork?

cytoplasmic projections

what connects the cells of neighboring sheets in the trabecular meshwork endothelium?

scleral spur

where do the trabecular sheets lose their endothelial covering?

collagenous & elastic fibers

what part of the trabecular sheets continues into the connective tissue of the scleral spur and ciliary body?

ciliary muscle

some connective tissue fibers of the ________ pass forward and merge with inner sheets of the meshwork

juxtacanalicular connective tissue

• located b/t the deepest trabeculae of the corneoscleral meshwork and Schlemm’s canal

• narrow strip of loose, cellular connective tissue

• majority of aqueous humor outflow resistance

• endothelial cells & fibroblasts embedded in a matrix of collagen, elastic-like fibers and ground substance

adhering & gap junctions

processes of cells in JCT are occasionally joined by what?

canal of Schlemm

• circular vessel

• venous channel

• normally contains aqueous humor

• “circular channel lined with bubble wrap”

• outer to trabecular meshwork

• anterior to scleral spur

• B

limbal sclera

external wall of canal of Schlemm lies against what?

JCT & scleral spur

inner wall of canal of Schlemm lies against what?

zonula occludens

what is the intercellular junction of the endothelial cells in the canal of Schlemm?

no

is the basement membrane of the canal of Schlemm complete?

giant vacuoles

pressure-dependent deformations of the inner wall of canal of schlemm that help move aqueous humor

provide an exit for aqueous humor, supply nutrients to avascular tissue

what are the functions of the filtration apparatus?

oxygen & glucose

aqueous humor provides what nutrients to the avascular lens and cornea?

pars plicata of ciliary body

where is aqueous humor produced?

convection currents

the aqueous humor circulates in what?

unconventional outflow

flow pattern of aqueous humor where it passes through spaces of uveal meshwork; less than 40% of outflow

I

uveal meshwork → connective tissue around ciliary muscles → suprachoroidal space → sclera or vortex veins

what is the flow route for the unconventional outflow pathway?

decreases with age

over the lifespan, the percentage of aqueous humor outflow that occurs via the alternate pathway …

contraction of ciliary muscle

what reduces the uveoscleral outflow?

scleral spur location

what determines whether aqueous humor enters the trabecular outflow pathway or the uveoscleral pathway?

above scleral spur

aqueous humor located _________ leaves the anterior chamber via the conventional pathway

below scleral spur

aqueous humor located ___________ leaves the anterior chamber via the unconventional pathway

unidirectional into the canal

what is the flow pattern through the giant vacuoles of the endothelial cells in the canal of Schlemm?

indentation forms in basal surface, gradually enlarges, and eventually opens to apical side, basal eventually occludes opening

what are the steps to a giant vacuole flow?

pinocytic vesicles

what provides additional transport into the canal of Schlemm?

passive diffusion

how does the bulk of aqueous humor go into the canal of schlemm?

cellular factors, increase

endothelial cells of trabecular meshwork may release ________ that can _______ permeability of inner wall of Schlemm’s canal

internal collector channels of Sondermann

• evaginations, blind pouches, of the internal wall of Schlemm’s canal that extend into the JCT toward the trabecular meshwork

• can be fairly long and branching

• serve to increase surface area

• arise near posterior canal wall

sheet of connective tissue

what always separates the endothelium of collector channels from the trabecular space?

frequently, bridges

corneoscleral trabecular sheets branch _______ and their endothelial cells often form ______ between adjacent sheets

ophthalmic veins

what carries aqueous humor out of the orbit?

30

how many external collector channels are there?

external collector channels

exhibit smooth muscle, 30 located around the eye, lead from outer wall of canal of Schlemm and toward vessels of episclera

deep scleral plexus

from the external collector channels, aqueous passes into this tortuous system of vessels within the thickness of the sclera

superficial intrascleral venous plexus

deep scleral plexus leads to this

aqueous and blood get mixed

tortuous route of draining of canal of schlemm causes what?

aqueous veins of Ascher

unique vessels in 10% of eyes that allow aqueous to bypass the tortuous pathway and connect directly from Schlemm’s canal to episcleral veins

near limbus at 3 or 9 o’clock

where are aqueous veins of Ascher located if present?

remains constant

how does aqueous humor production change over time?

decreased outflow

most cases of increased IOP are caused by what?

uveoscleral

which outflow pathway is said to be fairly constant and not affected by IOP

widening space between sheets and decreasing outflow resistance

how does ciliary muscle contraction alter the geometry of the trabecula?

JCT → endothelium of Schlemm’s canal

what are the elastic fibers of the scleral spur continuous with?

increases

interaction between elastic fibers of scleral spur, JCT, and Schlemm’s canal during accommodation ______ lumen diameter

Fin=Fout

ideal aqueous balance

tonometer

device to measure IOP

indentation/impression tonometer

measure the depth of indentation made by a plunger of known weight placed onto the cornea

applanation tonometer

measure the force required to flatten a known area of the corneal surface

applanation

which form of tonometry is the most widely used?

goldmann tonometry

measures the force required to flatten a known area of the cornea, based on imbert-fick law

non contact tonometry

time required to applanate 3.6mm diameter of central cornea with a standardized air pressure puff

central corneal thickness

measurements of eye pressure are affected by what?

555um

what is the average central corneal thickness

artificially high

increased CCT may lead to an _____ IOP

artificially low

decreased CCT may lead to an _____ IOP

LASIK

procedure that reduces corneal thickness and thus may reduce IOP readings

cholinergic agonist

• drug that affects IOP

• causes iris sphincter and ciliary muscles to contract, changing the configuration of trabecular sheets to facilitate outflow

• uncomfortable side effects of miosis and ciliary spasm

• not commonly used anymore

• Pilocarpine

carbonic anhydrase inhibitors

• drug that affects IOP

• not well tolerated

• inhibit key enzymes for ionic transport across epithelial layers

prostaglandins

• drugs that affect IOP

• currently most effective

• well tolerated, good compliance

• enhance outflow through uveoscleral pathway

• relax ciliary muscle tone

• remodel extracellular matrix w/in CT b/t muscle bundles, increasing spacing and tissue permeability

rho-kinase inhibitors

• drugs that affect IOP

• loosen intercellular junctions along Schlemm canal and decrease production of ECM, thus widening spaces in TM

• Rhopressa

argon laser trabeculoplasty

• uses higher laser energy that damages the TM causing it to contract and scar

• opens up pores to increase outflow

• recruits macrophages to treatment site where they remodel ECM to increase outflow

• one time permanent procedure

selective laser trabeculoplasty

• lower laser energy absorbed selectively by pigmented trabecular meshwork to recruit macrophages to clean up meshwork and increase outflow

• no damaging effects

• can be repeated as effects wear off

trabeculectomy

• last resort treatment for glaucoma

• wedge of TM is removed and often a scleral flap is formed so that aqueous can percolate through trabecular opening and accumulate beneath the flap to be absorbed into episcleral tissue

endoscopic cyclophotoagulation

recent surgical procedure that reduces aqueous production by applying a laser to damage tissue of ciliary processes

TM thickens, loss of uveal endothelial cells, hypertrophy of leftover cells, plaque formation, compacting uveal strands, reduced forming of giant vacuoles, atrophy of ciliary muscle, decrease in facility offset by decrease in aqueous production

what are aging changes in the TM?

beta blockers

medication that inhibits the receptor that upregulates sympathetic innervation to aqueous production; yellow cap

alpha2 agonists

medication that stimulates the receptor that downregulates sympathetic innervation to aqueous production; purple caps

carbonic anhydrase inhibitors

interferes with the regulator of bicarbonate transport that regulates fluid transport; orange cap

rho kinase inhibitor

medication that increases aqueous outflow through the conventional pathway; white cap

prostaglandin analog

medication that increases aqueous outflow through the unconventional pathway; blue cap

gonioscopy

• allows a direct view of the anterior chamber angle

• lens contains mirrors to look in and around the limbus to view angle structures

ciliary body, scleral spur, TM, Schwalbe’s line

what are the structures in the anterior chamber angle that can be viewed through gonioscopy? + iris

no

can Schlemm’s canal normally be seen in gonioscopy?

van herick angle estimation

used to estimate how wide open the anterior chamber angle might be to know if you can apply dilation

iris, ciliary body, scleral spur, TM, schwalbe’s line

what are the structures viewed in gonioscopy from posterior to anterior?