Anterior Chamber & Iris

the AC is more shallow in the ____________

periphery

depth and diameter of AC

depth: 3.6 mm

diameter: 11-12 mm

how much fluid can the AC hold

120-170 microns

average IOP

15.5 mmHg

boundaries of AC

anterior: corneal endothelium

peripheral: TM, Schlemm’s canal, CB, iris root

posterior: anterior iris

internal scleral sulcus

corneal scleral junction where the aqueous is filtered

structures in the corneal scleral sulcus (back to front)

peripheral iris, ciliary body, scleral spur, TM, schlemm’s canal, schwalbe’s line

Becker-Schaffer grading system

grades the AC angle based on most posterior structure visible

Becker-Schaffer classification

grade 4: CBB

grade 3: SS

grade 2: 1/3-1/2 TM

grade 1: only anterior TM or Schwalbe’s line

grade 0: no structures visible

Van-Herick grading system

based on width of AC angle compared to width of optic section

Van-Herick classification

grade 4: 1/2-1

grade 3: 1/4-1/2

grade 2: ¼

grade 1: less than ¼

grade 0: no space visible

scleral spur

circular band of collagen and elastin that extends from the inner part of the sclera

what structures originate off of the scleral spur

posteriorly: longitudinal ciliary muscle fibers

anteriorly: TM lamellae

what parts of the sclera contain elastin

scleral spur, lamina cribrosa, lamina fusca

what is the major role of the TM

aqueous humor filtration

shape and positioning of TM

lines the AC circumferentially

triangular: base abuts scleral spur and apex points towards cornea and Schwalbe’s line

what lines the external border of TM

juxtacanalicular tissue

where is the greatest amount of pigment in the TM

inferior part of angle

where is the best place to start gonio and why

inferiorly

TM has most pigmentation there

layers of TM (inner to outer)

uveoscleral meshwork > corneoscleral meshwork > juxtacanalicular tissue

2 divisions of TM

uveoscleral meshwork

corneoscleral meshwork

the uveoscleral meshwork is the (innermost/outermost) layer of the _____, consisting of (large/small) pores and ___ number of layers

the uveoscleral meshwork is the innermost layer of the TM, consisting of large pores and 1-5 layers

layer of TM inward to the scleral spur and adjacent to the AC

uveoscleral

composition of uveoscleral meshwork

large pores in a network of cords

inner core of collagen, elastin, and ground substance

surrounded by endothelium and BM

role of endothelial cells in uveoscleral meshwork

protein synthesis

lysozymes for phagocytosis of melanin and debris

uveoscleral meshwork (DOES/DOES NOT) use schlemm’s canal for outflow

does not

the uveoscleral meshwork is pressure (dependent/independent)

independent

2 possible paths of aqueous humor drainage in uveoscleral outflow

1. AH flows between the ciliary muscle fibers, into the suprachoroidal space, and through the sclera

2. AH drains through the anterior ciliary veins or vortex veins

what % of aqueous outflow is the uveoscleral meshwork responsible for

5-35%

how do prostaglandins increase uveoscleral outflow

decrease resistance in uveoscleral meshwork by relaxing the ciliary muscle and changing the ECM to increase uveoscleral outflow

the corneoscleral meshwork is located (closer/further) from Schlemm’s canal than the uveoscleral meshwork

closer

what 2 structures does the corneoscleral meshwork extend between

scleral spur and cornea

the corneoscleral meshwork consists of the (inner/outer) ____ (number) layers of the TM

outer 8-15 layers

composition of the corneoscleral meshwork

small pores within a network of sheet-like fibers similar to the uveoscleral cords

where are the smallest pores in the TM located

closest to Schlemm’s canal and within the juxtacanalicular tissue

other name for juxtacanalicular tissue

cribriform layer

what separates Schlemm’s canal from TM

juxtacanalicular tissue

what is juxtacanalicular tissue composed of

endothelial cells and ECM

what is the site to most resistance to outflow in the TM and why

juxtacanalicular tissue

has the fewest and smallest pores

why is the outflow of the corneoscleral meshwork pressure dependent

to penetrate the endothelial tight junctions that line Schlemm’s canal and the endothelial cells that fill the lumen, the IOP has to be higher than the episcleral venous pressure

AH must use high to low pressure gradient

biggest difference between uveoscleral and corneoscleral meshwork

UM is pressure independent

CM is pressure dependent

what % of AH drains through Schlemm’s canal

up to 90%

what is Schlemm’s canal

circular venous channel lined by endothelial cells where most AH drains

what structures are adjacent to the inner and outer border of Schlemm’s canal

inner border: (closest to AC, deeper in the eye) against scleral spur and TM (juxtacanalicular tissue)

outer border: against the sclera near the limbus

what are the walls of Schlemm’s canal lined with

endothelial cells

what is the difference between the linings of the inner and outer walls of Schlemm’s canal

endothelial cells of inner wall contain giant vacuoles that transport AH across the JXT into the canal

endothelial cells of outer wall do not have vacuoles, but the outer wall has a thin CT covering and efferent vessels that drain the AH out of the eye

what is the purpose of CT septae in Schlemm’s canal

form multiple channels that increase the surface area for AH filtration

internal collector channels

channels formed by CT septae that increase the surface area in Schlemm’s canal for AH filtration

what ultimately drains AH out of the eye

episcleral venous plexus

2 routes AH can drain out of Schlemm’s canal

1. external collector channels (efferent vessels) > deep scleral venous plexus > intrascleral venous plexus > episcleral venous plexus

2. aqueous veins of ascher > episcleral venous plexus

path of episcleral venous plexus drainage to heart

episcleral venous plexus > anterior ciliary veins > muscular veins > superior/inferior ophthalmic veins > cavernous sinus > superior/inferior petrosal sinus > internal jugular vein > brachiocephalic vein > superior vena cava > right atrium of heart

where does episcleral venous plexus directly drain to

anterior ciliary veins

Schwalbe’s line represents termination of _________

descemet’s membrane

what is Schwalbe’s line

area of collagenous CT that represents termination of Descemet’s membrane and delineates outer area of the limbus

posterior embryotoxon

anteriorly displaced Schwalbe’s line

iris

circular structure dividing anterior and posterior chambers

pupil location

opening in iris slightly nasal and inferior to center

pupil diameter under normal illumination

3-4 mm

Schwalbe’s contraction furrows

located at pupillary margin of iris

variations in thickness of posterior pigmented iris epithelium

average iris width

12 mm

where is the iris thickest

collarette region

where is iris thinnest

iris root (0.5 mm)

collarette

circular ridge 1.5 mm from pupillary margin that is site of attachment for fetal pupillary membrane during embryogenic development

has active iris vessels and remnants of old fetal vessels

what divides the iris into pupillary and ciliary zones

collarettes

2 zones of the iris

pupillary zone, ciliary zone

ciliary zone of iris

has iris furrows that allow iris tissue to bunch towards periphery during dilation

has radial streaks that are white and represent collagen in the iris vessels

radial streaks of iris

in ciliary zone, collagen in the iris vessels

difference between ciliary zone and pupillary zone of iris

pupillary zone has smaller radial streaks because iris BVs are smaller towards the pupillary margins

location of crypts of Fuchs

anterior border layer of iris

span the collarettes into pupillary and ciliary iris zones

aniridia

bilateral condition with complete or partial absence of iris

patients have poor vision (foveal hypoplasia), subsequent nystagmus

can also have microcornea, lens subluxation, and ON hypoplasia

disease highly associated with aniridia and why

glaucoma

PAS can cause angle closure

layers of iris front to back

anterior border layer, iris stroma, anterior epithelium & dilator muscle, posterior pigmented epithelium

anterior layer of iris

anterior border layer

contents of anterior border layer of iris

fibroblasts, melanocytes, collagen fibrils

function of anterior border layer of iris

provides colors to iris

what determines iris color

amount of melanin in iris melanocytes

not the number of melanocytes

in a blue iris, anterior border is (thick/thin) and melanocytes have ___________

anterior border is thin

melanocytes have a small amount of melanin

in a brown iris, anterior border is (thick/thin) and melanocytes have ___________

anterior border is thick

melanocytes have a large amount of melanin

what color of irises have heavily pigmented two iris epithelial layers

both brown and blue irises

condition characterized by a lack of pigment in the iris epithelial layers

oculocutaneous albinism

what are iris crypts

collagenous columns in the anterior border layer that serve as passageways for AH to enter the iris stromah

heterochromia

difference in eye color between eyes

what can cause heterochromia

congenital

topical prostaglandins

chronic inflammation (uveitis)

what is the iris stroma composition

vascularized loose collagen network

iris stroma has (more/less) cells than the anterior border layer

less

iris stroma is continuous with the stroma of the ____________

ciliary body

what is contained in the iris stroma

cells, nerves, blood vessels, sphincter muscle

nerves in the iris stroma

LPCNs and SPCNs

sensory fibers and sympathetic fibers of the LPCNs and SPCNs

parasympathetic fibers of the SPCNs

what kind of blood vessels are in the iris stroma (and their junctions) and what do they form

non-fenestrated BVs with zonula occludens junctions

form part of the blood-aqueous barrier

what are the blood vessels in the iris

major arterial circle

minor arterial circle

radial veins and radial arteries

location of major arterial circle of iris

located in the ciliary body

extends radially through the iris stroma up to the pupil marginwh

what forms the major arterial circle of the iris

anastomoses between the ACAs and LPCAs

location of the minor arterial circle of the iris

located in the iris stroma near the pupil margin, inferior to the collarette

what forms the minor arterial circle of the iris

anastomoses of the radial arteries branching off the major arterial circle of the iris

what veins drain blood from the iris

radial veins

path of blood draining through radial veins

radial veins (blood from iris) > ciliary body veins > choroidal veins > vortex veins > superior/inferior ophthalmic veins

the minor arterial circle of the iris is (fenestrated/non-fenestrated) and makes up part of the ______________

non-fenestrated (doesn’t leak)

makes up part of the blood-aqueous barrier

what layer of the iris is the sphincter muscle in

stroma

what forms the iris sphincter muscle

anterior iris epithelial cells that detach and migrate into the stroma and become smooth muscle cells

what kind of muscle is the iris sphincter

circular smooth muscle