Iris Flashcards
Iris
diaphragm b/n ant. and post. chambers
slightly convex because of lens
ant. portion of uveal tract
exposed to aqueous of ant. chamber
central - lens
lateral - aqueous of post. chamber
lens importance
gives convex shape
absence of lens = iris more flat (iridodonesis)
Collarette
site of minor circle (2 mm from pupil margin)
AKA pupillary frill
thickest part of iris
divides to pupillary zone and peripheral ciliary zone
iris root
thinnest region of the iris
inserts into antero-medial surface of ciliary body
more anterior insertion = narrower angle (hyperopes)
more posterior insertion = wider angle (myopes)
iris dimensions
diameter: 12 mm
circumference: 37-38 mm
thickest at collarette = 0.6 mm
thinnest at iris root = 0.5 mm
pupil
main function to limit amount of light
2mm - 8mm size
difference b/n pupil diameters = anisocoria
decentered (approx 0.5 mm)
anisocoria (physiologic)
detectable diff. b/n pupil diameters
20% of normal population
pupil size difference will be same in bright and dim illumination
horners (sympatheics a problem) if anisocoria diagnosis different illumination
pupillary ruff/pigment seam
margin of the pupil outlined with ring of pigment
iris coloration
determined by amount of pigment in iris stromal melanocytes
main influence is # of melanin granules and size located in anterior stromal melanocytes
brown most common
green, light brown, and hazel
blue less common
blue at birth because uveal tract not maximally pigmented
if iris stroma lacks pigment but posterior iris epithelium pigmented = blue
if no pigment in stroma and epithelium = pink (albinism)
albinism
iris stroma and posterior iris epithelium lacks pigment = pink iris
vision problem will occur from abnormal ret. development and abnormal patterns of nerve connections b/n eye and brain
variations and variability in iris color
iris freckles,
heterochromia (iridum vs iridis),
iris atrophy,
fuch’s heterochromia
iridocyclitis,
brushfeld spots(stroma hypoplasia seen with down synrome),
iris melanoma,
iris nevi,
latanoprost pharmaceutical agent
latanoprost use
accumulation of pigment and increase in melanin in stromal melanocytes rather than increased number of melanocytes
tell patient of color change
fuch’s heterochromic iridocyclitis
in young middle age adults, cataract patients, KP’s flare and cell, glaucoma
(hyperemia, pain, photophobia limited)
heterochromia iridis
one eye alone shows heterochromia
different color eyes
anterior iris surface
trabeculae: thick branching bands of surface cells and collagen that bridge spaces in anterior border layer of the iris
- pronounced around collartte and oriented radially
- bands enclose oval-shaped crypts: crypts of fuchs
long radial ridges seen in ciliary zone
contraction folds: circular folds in ciliary zone
pupillary ruff: at pupil - represents posterior iris epithelium extending anteriorly
posterior iris surface
lots of pigment provides smooth black velvety surface
radial furrows (radial contraction folds of schwalbe)
circumferential (circular) folds present in ciliary zone
iris contains
sphincter muscle and dilator muscle
3 layers of iris
anterior border layer: narrow layer of cells of fibroblasts and melanocytes
iris stroma
posterior iris epithelium
anterior border layer
discontinuous layer of fibroblasts and melanocytes; more compant than paucity of cells in stroma
crypts of fuch’s: absence of anterior border layer
iris processes: extensions of anterior border layer in anterior chamber angle
-few nerve filaments and capillaries here
anterior border layer cell types (2)
fibroblasts: flat stellate cells with microvilli and cilia projection into anterior chamber; they have radiating interdigitating processes with intercellular jxns
melanocytes oriented parallel to iris surface and beneath fibroblasts
iris stroma
compose of pigmented and nonpigmented cells and collagen fibers in proteoglycan matrix
contans blood vessels, nerves, and sphincter muscle
iris stroma cell arrangment and types
diffuse cellular arrangement
50-200um in diameter can diffuse here
fibroblast: principle cell type around blood vessels
melanocytes: processes arranged around blood vessels
mast cells
clump cells (type 1)
distinguised from other melanocytes by their darker brown color and round shape
bloated melanocyte: # and size increase with age (macrophages) that engulfed pigment granules
found in pupillary zone around the sphincter muscle (primarily anterior to sphincter muscle)
clump cells (type 2)
clusters of pigmented cells that represent migrated neuroepithelial cells
sphincter muscle
ring of smooth muscle in pupillary zone circular fibers
0.75 - 1.0 mm in diameter
parasympathetic innervation
action is pupil constriction
iris blood vessels - stroma
sinous course (corkscrew-like) to accommodate variable states of iris contraction
blood vessels follow meandering and radial path from iris root to pupillary zone
nonfenestrated vessels: tight jxn b/n endothelial cells establishes the blood-aqueous barrier
“tube within a tube” structure: outside endothelial wall, pericytes and collagen fibers from sheath that encloses the blood vessel (extra support system)
endothelium of bv designed to restict the movement of fluid and large molecules through capillary walls
establishment of blood-aqueous barrier
- non-fenestrated iris blood vessels
- tight jxn between apical sides of the non=pigmented epithelial cells of ciliary body
breaching the blood aqueous barrier results in the release of undesirable blood components into aqueous (as in nterior uveitis/iridocyclitis)
clinical findings in anterior uveitis
hallmark: flare and cell
flare: excess protein in aqueous
cell: presence of inflammatory cells in aqueous
(flare and cell will be visible with slitlamp biomicroscopy)
posterior synechia
adhesion between the iris at the pupil margin and the anterior lens surface
-thick and sticky aqueous causes iris to adhere to anterior lens
keraptic precipitates
flare and cell in anterior chamber
other blood-aqueous barrier breached
hyphema: blood in anterior chamber
hypopyon: pus/white cell accumulation in anterior chamber
posterior iris epithelium
neuroectoderm in origin
2 cell layers apposed apex to apex
myoepithelium: anterior epithelial layer
posterior epithelial layer
anterior epithelium (myoepithelium)
- basal processes extend in radial direction
- basal processes are arranged in overlapping (shingles on roof)
- sympathetic innervation to dilator (from iris root to pupillary margin gives radial appearance)
dilator muscle: overlapping basal processes and posterior epiethelial layer (columnar)
muscle spurs
anchor the dilator muscle to the stroma by thin muscle filaments
grunert’s spur: iris root
von michel’s spur: periphery of sphincter
fuch’s spur: midway along length of sphincter
posterior epithelial layer
heavily pigmented
consists of large cuboidal/columnar cells
microvilli separate anterior from posterior epithelial layers
apical surface tight jxn
lateral membranes: tight jxn and desmosomes
defects of posterior iris epithelium
loss of pigment = transillumination defect’s are created
loss of posterior iris pigment and its dispersion
suggested theory for defects: chafing of posterior pigmented epithelium against anterior lens zonules results in loss of pigment and creation of transillumination defects in iris and dispersion of pigment
pigment dispersion
all patients with pigment dispersion risk for pigmentary glaucoma
pigment on cornea - krukenberg spindles
pigment in angle, with potential for poor aqueous outflow and ultimately elevated IOP and pigmentary glaucoma
blood supply to iris
radial vessels in iris stroma
minor circle at collarette
vessels arise from major circle of iris (stroma ciliary body)
circle formed by: long posterior ciliary arteries (2) and anterior ciliary arteries (7)
venous drainage
venous vessels roughly follow arterial ones
larger veins in the anterior stroma and smaller ones near dilator
drain posteriorly and centrifugally into ciliary body -> vortex veins
nerve supply
rich supply of myelinated and unmyelinated nerves
branches of long and short posterior ciliary nerves (branches of nasociliary from CN 5)
innervation pathway to sphincter muscle
parasympathetic innervation (efferent) -> sphincter (pregang cell EW -> synapse in cil gang. -> axon of short ciliary nerve -> sphincter muscle)
innervation pathway to dilator muscle
pregang. cell bodies (lat horn T1 - T2) -> sup. cervical gang. (synapse) -> internal carotid artery -> dilator (via long ciliary nerves and short ciliary nerves)
sympathetical pathway to eye (innervation to dilatory muscle, tarsal muscle (mueller), uveal blood vessels)
axons ascend along carotid plexus – leave plexus into orbit as sympathetic root of ciliary ganglion and pass into short ciliary nerves to choroid
