Ocular Anatomy Exam II Anterior Chamber

Gonioscopy... where is the the "person" relative to the angle?

"Person standing *on iris* looking at angle*"

Schwalbe's line is the most (anterior/posterior) structure of the angle; circumferential ring of collage and elastin

*anterior* -anterior chamber's most anteriorly is sandwiched by cornea so if schwalbe's line is an extension of a *corneal* structure (descemet's) it *has to be anterior*

2 major gonioscopic subdivision: Anterior trabecular meshwork

- anterior to Schlemm's canal -non-filtering -light or no pigmentation (lack of filtration) -transition zone located adjacent to corneal endothelium -contains stem cell niche... does not undergo differentiation in vivo but are studied for glaucoma/retinal treatments

Define the uveal meshwork...

-Innermost part of TM -cordlike, larger pores -2-3 layers of sheets forming inner meshwork -adjacent to anterior chamber -*first sieve* (aqueous encounters this first) -very large intertrabecular spaces functions in *gross* filtration (large)

What is the scleral spur? What is it's function?

-Internal projection of the sclera; condensed stromal tissue with dense collagen bundles -behind TM -extension of scleral stroma with *more elastin* -origin of ciliary muscles and anchor for TM fibers

Clinical correlate: Normal angle structures but optic nerve damage, visual loss and high IOP?

-Unsure of pathophysiology/etiology -Problem could be in outflow areas: drain is getting clogged -Accelerated "aging" of anterior chamber angle

Schlemm's canal: Endothelial lining of *inner wall*

-Zonula occludens (TJ) must go through cell not intracellular -intracellular transport of aqueous by *giant vacuoles*

Functions of the Iris

-controls size of pupil and therefore amount of light reaching the retina

2 major gonioscopic subdivision: Posterior trabecular meshwork

-filtering portion -pigmented (degree of pigmentation depends on individual)

What are iris processes?

-found in 35% of normal eyes -extends from peripheral iris to TM -visualized during gonioscopy

Cribriform plexus

-found in juxtacanalicular tissue -elastic fibers connected to tendons from ciliary body muscles (longitudinal muscles) -connected to basal surface of endothelial cells of schlemm's canal inner wall -contraction of ciliary body pulls cribriform plexus = pulls inner wall of SC = opens SC for drainage -Contraction of ciliary body pulls scleral spur = pulls trabecular meshwork = enhances outflow

Define juxtacanalicular tissue/meshwork...

-located between last sheet of corneoscleral meshwork and inner wall of Schlemm's canal -*finest* sieve -*offers the greatest resistance to outflow of aqueous* = slows rate the most -Amorphous; collagen, microfibrils, ground substance -few endothelial cells -*most* GAGs = gel like slows down filtration = increase pressure -location of cribriform plexus*

Outer wall of Schlemm's canal: external collector channels

-main outflow -25-30 collecting tubes -runs circumferentially and some connects to each other -empty into *deep scleral plexus* then to *intrascleral plexus* then into *episcleral vein* then into *vortex vein* and finally to *ophthalmic vein* RECAP: 1. collecting tubes in a circular, interconnecting network 2. dumps into deep scleral plexus 3. intrascleral 4. episcleral vein 5. vortex vein 6. opthalmic vein

Schlemm's canal: Outer wall

-next to sclera -zonular occludens (TJ) -does not contain vacuoles

Where is Schlemm's canal? How can it be visible in gonioscopy?

-peripheral to posterior trabecular meshwork (highly pigmented) and part of the *"filtration apparatus"* -only see in gonioscopy if filled with blood (not common!)

Functions of endothelial cells lining trabecular meshwork

1. phagocytosis (lysosomes) 2. secretion of GAG's to control/*slow down* flow of aqueous 3. Lysosomal enzymes = control amount of GAGs (breaks it down); steroid responder inhibiting break down of GAGs = decreasing aqueous outflow, increased IOP or *steroid induced glaucoma* 4. Tissue repair by protein synthesis and connective tissue synthesis (produces collagen, elastin, and other proteins)

Index of refraction of aqueous

1.336 (close to water's 1.333)

Depth of the anterior chamber can be measure by what type of scan?

A Scan

Changes which occurs in anterior chamber angle with age...

A. Increase of IOP B. Oxidative damage to trabecular meshwork C. Plaques in juxtacanalicular tissue D. Decreases in number of endothelial cells that line TM (larger in size) E. Decreases in giant vacuoles F Accumulation of pigment from iris and ciliary body in meshwork G. Decreased phagocytic activity of endothelial cells because of changes in cytoskeleton H. Hyalinization/thickening of trabeculae (TM)

What are the functions of the anterior chamber angle?

A. pathway for aqueous exit B. nutrients to deep limbal and scleral tissue (aqueous) C. self-cleaning filter so no clogging D. Phagocytosis E. Production of mucopolysaccharides and enzymes (Glycosaminoglycans (GAGs) or mucopolysaccharides) highly polar and attract water; functions as a lubricant or as a shock absorber F. Rectifying properties= one way movement of fluid (OUT never in) (make everything "right" = rectifying)

Where does aqueous from the anterior chamber exits at?

Anterior chamber angle *"filtration apparatus"*= trabecular meshwork and schlemm's canal (peripheral to AC) ~20-45 degrees

What are the borders of the anterior chamber?

Anterior- corneal endothelium (*cornea*) (remember Na+/K+ pumps) Peripheral- trabecular meshwork (anterior chamber angle) Posterior- anterior iris surface (*iris*) and anterior *lens* Angle- where iris and cornea meet; aqueous humor exits the anterior chamber here

Gonioscopically, how can you divide the trabecular meshwork? Where is it "found"?

Anterior= on top of Schlemm's canal,non-filtering, less pigment, niche for stem cells Posterior= "deep" in angle closer to iris defined by *darker pigmentation*, high filtration activity, drains into Schlemm's canal Found between Schwalbe's line and scleral spur Cornea's descemet (anterior) -> Schwalbe's line Corneal endothelium -> trabecular meshwork Sclera-> underneath cornea

What is the purpose of aqueous humor?

Carries necessary metabolites (oxygen and glucose) to avascular cornea and lens

True or False Due to the high amount of water content, aqueous is not considered a colloid

FALSE small proteins containing still classified as colloid

True or False Trabecular meshwork's porous sheets, in filtration, are all one sized pores

FALSE variety of sizes = efficiency of filtration

Anterior chamber angle structures from *posterior to anterior* Note: Bands as seen from plane of iris (posterior) to the limbus (anterior)

I CAN'T SEE THIS STUFF!!! I= iris C= ciliary body S= scleral spur T= trabecular meshwork S= schwalbe's line *MUST KNOW THIS ANTERIOR TO POSTERIOR AS WELL*

Clinical correlate (aqueous flow): Krukenberg spindles

If pigment present in anterior chamber will follow convection current pattern and be deposited on the cornea in vertical pattern

Clinical importance of aqueous: Glaucoma

Increased aqueous production and/or decreased outflow results in IOP

What would happen if aqueous humor composition was altered to include greater amount of proteins?

Increased proteins = increased viscosity --> decrease outflow of aqueous --> increase IOP

Where are the most GAGs found in TM?

Juxtacanalicular tissue (last layer before Schlemm's canal)

Explain WHY we need to have little proteins in aqueous that pertains to CLARITY of image produced

Less proteins = less light scattering effect = aqueous is transparent as possible

Clinical correlate: Pilocarpine

Older glaucoma medication (not used except in third world countries) -parasympathomimetic (mimics parasympathetic) -changes in orientation of trabecular meshwork and enhances aqueous outflow -bad side effects; contraction of ciliary muscle = blur = brow aches, headaches= miotic pupils (small pupils)

-Schwalbe's line- Clinical correlate: Sampaolesis Line

Pigmented Schwalbe's line

Clinical correlate: Blood in Schlemm's Canal

Remember it is considered a venous channel but does not contain blood (contains aqueous humor). Too much pressure can cause blood to be in SCC but it *cannot enter anterior chamber* due to the *vacuole system*

Triangular shape of trabecular meshwork: Apex

Schlemm's canal

Triangular shape of trabecular meshwork: Base

Sclera spur and ciliary body (anterior surface)

True or False IOP is highest in the morning due to lysosomal enzymes' diurnal cycle

TRUE -build up of GAGs (decrease filtration increased fluid accumulation) until lysosome can break it down

True or False Most cases of IOP is caused by decreased aqueous outflow but normal production

TRUE production is usually alway constant it is the *exiting* that is the culprit

Which of these processes are passive process in aqueous production and flow? (pick 2) a. diffusion b. ultrafiltration c. active secretion

a. diffusion b. ultrafiltration

Innervation of trabecular meshwork's endothelial cells

a. sympathetic b. epinephrine = speeds up filtration

Triangular shape of trabecular meshwork: Inner face

anterior chamber

Functions of the Ciliary Body

i. accommodation ii. production and outflow of aqueous iii. contributes some components to vitreous iv. forms blood-aqueous barrier v. absorption of light

Schlemm's canal: Internal collector channels of Sondermann

-found in inner wall of endothelium -outpouchings of SC so not real channels -increase surface area and allows for more giant vacuole formation (intracellular transport of aqueous)

Uveal scleral outflow pathway

-unconventional pathway -face of ciliary body or anterior border layer of iris (loose tissue, not absorbed into vasculature system here because vessels are non-fenestrated) -percolates through ciliary muscle between muscle fibers and loose CT -travels in supraciliary space -suprachoroidal space -drains in vortex veins Enhanced by: -low levels of prostaglandins -Xalatan/Travatan/Lumigan/Zioptan -> low lvl prostaglandin, gold standard glaucoma, increases uveal scleral pathway and bypass Schlemm's canal

From birth to age 80 there is a 25% decrease in aqueous production and therefore a 25% decrease in aqueous flow

...

What are the three fluid filled chambers of the eye?

1. Anterior chamber (aqueous) 2. Posterior chamber (aqueous) 3. Vitreous chamber (vitreous)

What two mechanisms enhances outflow of aqueous fluid?

1. Ciliary body pulls cribriform plexus = pulls Schlemm's canal inner wall open 2. Ciliary body pulls scleral spur = trabecular meshwork opens

Two major pathways for aqueous outflow

1. Schlemm's canal 2.Uveal scleral outflow pathway

What is responsible for the blood aqueous barrier? 1. ciliary body 2. trabecular meshwork 3. schlemm's canal 4. the whole uveal tract

1. ciliary body

Outer wall of schlemm's canal drains to venous system by two ways...

1. external collector channels: main outflow route 2. aqueous veins (of Ascher): minor route of drainage

Determinants in the openness of angle

1. genetics 2. gender (larger = male) 3. age (decreased with age due to increase in lens) 4. refractive error (hyperopes = narrow angle) 5. race (asians = narrow; blacks = more open; caucasian= most open)

What are the two most important factors in angle openness? (pick two) 1. genetics 2. gender 3. age 4. refractive error 5. race

1. genetics 4. refractive error

Which wall of Schlemm's canal contains vacuoles for intracellular movement of aqueous? 1. inner wall 2. outer wall 3. both 1 and 2 contains vacuoles

1. inner wall

Pathway of aqueous humor

1. produced by pars plicata (ciliary epithelium) of ciliary body 2. secreted into posterior chamber through epithelium covering ciliary process and moves forward 3. passes b/w iris and lens into anterior chamber through pupil 4. exits through anterior chamber angle

Volume of the anterior chamber

250 microliters

Put these race in order or most openness to smallest angle 1. blacks 2. asians 3. caucasians

3. caucasians > 1. blacks > 2. asians

What is the posterior boundary of the anterior chamber? (select 2) 1. trabecular meshwork 2. schlemm's canal 3. corneal endothelium 4. iris 5. pupillary area of lens

4. iris 5. pupillary area of lens

Describe the circulation of the aqueous in the anterior chamber

Convection currents -down from cooler cornea (due to a vascularity) -up from warmer iris

Aqueous supplies what?

Cornea (partial) Lens (entire) Vitreous Anterior chamber angle structures

Schwalbe's line is an extension of what corneal structure?

Descemet's membrane

Schwalbe's line serves as a transition between corneal and trabecular meshwork (endothelium/epithelium)

ENDOTHELIUM (most posterior part of cornea)

Clinical correlate: aging's effects on filtration

Endothelial cells decrease in amount (increase in size) with age so less tissue repair, less phagocytosis, less secretion in general = glaucoma? other age related eye diseases

True or False The closer to Schlemm's canal the larger the pores become

FALSE

True or False Aqueous is similar to plasma but with more protein concentration

FALSE Less protein than plasma

True or False Schlemm's canal is considered to be a *venous channel* and carries blood

FALSE Venous channel that carries aqueous humor

True or False Ciliary body is visible during gonioscopy all the time

FALSE may or may not depends on openness of angle

What is trabecular meshwork made out of?

It is "modified *corneal endothelium*" (TM is continuous with corneal endothelium) Superimposed layers of fenestrated connective tissue sheets (connective tissue cords branch & interlaced to form porous sheet) Contains collagen and elastic fiber core GAGs (negative polar = binds to water; forms gel = filtration) Covering = corneal endothelium Recap: -Outer capsule of *corneal endothelium* -Connective tissue sheets made out of *collagen*, *elastic fiber* and *GAGs*

What enhances uveal scleral pathway?

Low levels of prostaglandin

Known that aqueous has lack of proteins (compared to plasma), would you say it is highly or low in viscosity?

Low viscosity -directly proportional to protein content -aqueous is mostly water (98%)

Clinical correlate: Prescribing steroids

Lysosomal enzymes are *inhibited* by *steroids* which means that there is in an INCREASE in GAGs.... slows down rate of filtration... accumulation of aqueous fluid in anterior chamber... increased IOP... *steroid-induced glaucoma* !!very bad check IOP before prescribing meds!!

Clinical importance of keeping aqueous volume constant?

Maintaining stable IOP within the eye -IOP kept at a level not detrimental to ocular tissue -Rate of production and rate of exit stable

Schlemm's canal ONE WAY process of aqueous

Rectifying properties of giant vacuoles: pressure gradient created by slower moving aqueous in the juxtacanalicular trabecular meshwork prevents back flow of aqueous *Thao's laymen explanation: So you have this HIGH pressure on one side caused by aqueous accumulation and your body wants it to LEAVE but if you move it TOO FAST then there will not be pressure and there could be BACKFLOW. The pressure also helps in the formation of these GIANT VACUOLES that is the only way aqueous can be moved through the cell barrier because it has tight junctions (intracellular movement). Basal side (most aqueous side) is where vacuole forms and as it pinches off it sucks up a certain amount of aqueous then travels through the cell and then binds on the other side of the membrane and releases aqueous into the lumen of schlemm's canal for exit

True or False The higher the IOP the *more* vacuoles there are

TRUE Pressure dependent remember?

-Schwalbe's line- Clinical Correlate: posterior embryotoxon

Thickened Schwalbe's line (15-20% of pop.) Visualized with slit lamp at limbus

True or False Hyperopes have smaller angles than myopes

True

True or False The aqueous is relatively isotonic

True -does not pull fluid from surrounding tissue such as the lens and cornea

True or False Trabecular meshwork technically covers all of the anterior chamber angle

True Functions as a *filter* so needs to cover other structures

Gonioscopy

Use of goniolens/gonioscope in conjunction with slit lamp to gain a view of the anterior chamber angle or anatomical angle formed between eye's cornea and iris

What type of inflammation would increase proteins in aqueous humor?

Uveitis (ciliary body!!! = breakdown of aqueous blood barrier) increased proteins would produce tyndall effect during slit lamp examination

Gold Standard in Glaucoma Treatment

Xalatan Travatan Lumigan Zioptan bypasses Schlemm's canal and increase uveal scleral pathway

Where do you find the most amount of aqueous? a. anterior chamber b. posterior chamber c. vitreous chamber

a. anterior (250 microL) -posterior contains 60 microL) -vitreous contains vitreous not aqueous (duh)

Peak flow of aqueous is at ____ years old a. 1-10 b. 10-20 c. 20-30 d. 30-40

b. 10-20

What produces aqueous? a. Schlemm's canal b. Ciliary body c. Iris d. Scleral spur e. Endothelial cells of TM

b. ciliary body *par plicata of ciliary body* -pars plicata is the folded and most anterior portion of the ciliary body of an eye

Which of these process accounts for 80% of total aqueous formation? a. diffusion b. ultrafiltration c. active secretion

c. active secretion (requires energy)

In which subdivision of trabecular meshwork is there the most control of aqueous rate? Greatest resistance to aqueous outflow? a. uveal meshwork b. corneoscleral meshwork c. juxtacanilicular meshwork

c. juxtacanalicular meshwork tissue

Corneal endothelial cells are different from trabecular meshwork endothelial cells in that its... a. endothelial cells are very metabolically active b. they do not undergo mitosis c. decrease in number but increase in size as we age d. cells are more regular in shape

d. cells are more regular in shape a-c are how they are *alike*

What part of the trabecular meshwork secretes GAGs and lysosomal enzymes? a. collagen sheets b. elastin core c. keratocytes d. endothelial cells

d. endothelial cells

Clinical correlates: Narrow angles/narrow insertions of iris

dilation can be risk for angle closure glaucoma dilation--> iris rolls up (gets fatter) --> angle gets more narrow --> angle closure glaucoma!

Clinical importance of aqueous: Post surgical evaultion

i. after cataract and lasik curriery composition of aqueous should be examined to check for any extraneous cells or foreign material ii. condition of aqueous is an indicator to how successful surgery was and how well eye is healing

Clinical importance of aqueous: Uveitis (iridocyclitis)

i. inflammation of uveal tract ii. iridocyclitis inflammation of iris and ciliary body iii. breakdown of blood aqueous barrier (ciliary body responsible for this) -> changes in aqueous composition iv. uveitis may lead to *secondary glaucoma*

Conventional Pathway: Schlemm's canal

i. tight junctions = goes through cells ii. intracellular via pressure dependent vacuole system iii. internal collector channels of Sondermann in inner wall of endothelium to increase SA and production of giant vacuole iv. outer wall that drains by two ways: 1. external collector channels 2. aqueous veins of ascher v. accomodate 80% of aqueous outflow

Pleomorphism

increase in size (cell size)

Triangular shape of trabecular meshwork: Outer sides

lies against corneoscleral stroma and Schlemm's canal

Tyndall effect

light scattering by particles in a colloid (i.e. aqueous)

Ciliary body location...

middle structure of urea continuos with iris anteriorly choroid and retinal posteriorly

What happens when excess debris are filtered through the trabecular meshwork?

stresses the endothelium and may decrease filtering aqueous meshwork may be clogged --> *glaucoma* (buildup of pressure inside the eye) damaged cells can't digest anymore

Define corneoscleral meshwork...

trabecular meshwork near corneoslceral stroma -outer portion of trabecular meshwork -formed by 20 sheets; pores not aligned when stacked so acts like a sifter -located closer to Schlemm's canal deep to uveal meshwork

Aqueous: "Lymphatic drainage"

trabecular meshwork serves as the path for large molecular weight molecules to exit with aqueous

Aqueous acts like a "________ drainage" in the elimination of metabolic wastes from avascular tissue

venous drainage (lens, cornea, vitreous and ant. chamber angles)