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Ocular Biology > Iris > Flashcards

Iris Flashcards

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1
Q

Iris

A

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

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2
Q

lens importance

A

gives convex shape

absence of lens = iris more flat (iridodonesis)

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3
Q

Collarette

A

site of minor circle (2 mm from pupil margin)

AKA pupillary frill

thickest part of iris

divides to pupillary zone and peripheral ciliary zone

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4
Q

iris root

A

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)

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5
Q

iris dimensions

A

diameter: 12 mm
circumference: 37-38 mm

thickest at collarette = 0.6 mm

thinnest at iris root = 0.5 mm

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6
Q

pupil

A

main function to limit amount of light

2mm - 8mm size

difference b/n pupil diameters = anisocoria

decentered (approx 0.5 mm)

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7
Q

anisocoria (physiologic)

A

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

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8
Q

pupillary ruff/pigment seam

A

margin of the pupil outlined with ring of pigment

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9
Q

iris coloration

A

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)

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10
Q

albinism

A

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

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11
Q

variations and variability in iris color

A

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

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12
Q

latanoprost use

A

accumulation of pigment and increase in melanin in stromal melanocytes rather than increased number of melanocytes

tell patient of color change

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13
Q

fuch’s heterochromic iridocyclitis

A

in young middle age adults, cataract patients, KP’s flare and cell, glaucoma

(hyperemia, pain, photophobia limited)

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14
Q

heterochromia iridis

A

one eye alone shows heterochromia

different color eyes

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15
Q

anterior iris surface

A

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

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16
Q

posterior iris surface

A

lots of pigment provides smooth black velvety surface

radial furrows (radial contraction folds of schwalbe)

circumferential (circular) folds present in ciliary zone

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17
Q

iris contains

A

sphincter muscle and dilator muscle

18
Q

3 layers of iris

A

anterior border layer: narrow layer of cells of fibroblasts and melanocytes

iris stroma

posterior iris epithelium

19
Q

anterior border layer

A

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

20
Q

anterior border layer cell types (2)

A

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

21
Q

iris stroma

A

compose of pigmented and nonpigmented cells and collagen fibers in proteoglycan matrix

contans blood vessels, nerves, and sphincter muscle

22
Q

iris stroma cell arrangment and types

A

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

23
Q

clump cells (type 1)

A

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)

24
Q

clump cells (type 2)

A

clusters of pigmented cells that represent migrated neuroepithelial cells

25
Q

sphincter muscle

A

ring of smooth muscle in pupillary zone circular fibers

0.75 - 1.0 mm in diameter

parasympathetic innervation

action is pupil constriction

26
Q

iris blood vessels - stroma

A

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

27
Q

establishment of blood-aqueous barrier

A
  1. non-fenestrated iris blood vessels
  2. 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)

28
Q

clinical findings in anterior uveitis

A

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)

29
Q

posterior synechia

A

adhesion between the iris at the pupil margin and the anterior lens surface

-thick and sticky aqueous causes iris to adhere to anterior lens

30
Q

keraptic precipitates

A

flare and cell in anterior chamber

31
Q

other blood-aqueous barrier breached

A

hyphema: blood in anterior chamber
hypopyon: pus/white cell accumulation in anterior chamber

32
Q

posterior iris epithelium

A

neuroectoderm in origin

2 cell layers apposed apex to apex

myoepithelium: anterior epithelial layer

posterior epithelial layer

33
Q

anterior epithelium (myoepithelium)

A
  • 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)

34
Q

muscle spurs

A

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

35
Q

posterior epithelial layer

A

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

36
Q

defects of posterior iris epithelium

A

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

37
Q

pigment dispersion

A

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

38
Q

blood supply to iris

A

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)

39
Q

venous drainage

A

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

40
Q

nerve supply

A

rich supply of myelinated and unmyelinated nerves

branches of long and short posterior ciliary nerves (branches of nasociliary from CN 5)

41
Q

innervation pathway to sphincter muscle

A 
parasympathetic innervation (efferent) -> sphincter 
(pregang cell EW -> synapse in cil gang. -> axon of short ciliary nerve -> sphincter muscle)
42
Q

innervation pathway to dilator muscle

A

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

Ocular Biology (9 decks)

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