THE IRIS Flashcards
(41 cards)
The iris root joins the iris to which of the following structures?
Pars plicata of the ciliary body
Which of the following areas of the iris is the thickest?
Collarette
Which of the following areas of the iris thickens during dilation?
Ciliary zone
The sphincter pupillae muscle is found in which of the following iris layers?
Stroma
An iris nevus is an anatomical variant found in which of the following iris layers?
Anterior border layer
Which 4 characteristics best describe the sphincter pupillae muscle?
Composed of smooth muscle
Leads to constriction
Located in the stroma
Located in the pupillary zone
FILL IN
The sphincter pupillae muscle receives preganglionic parasympathetic innervation from neurons whose cell bodies lie in the ____ (Edinger-Westphal) nucleus.
Postganglionic parasympathetic neuron cell bodies lie in the _____ (ciliary) ganglion and their axons form the _____(short posterior ciliary nerves) that innervate the iris sphincter
The major arterial circle of the iris is located in the:
ciliary body stroma
Cells and flare in the anterior chamber represent damaged _____
Zonula occludens junctions
The 2nd neuron in the sympathetic innervation pathway of the dilator pupillae muscle runs between which 2 of the following structures?
Ciliospinal center of Budge, Superior cervical sympathetic ganglion
An iris cyst is fluid that accumulates between which 2 of the following iris layers?
Anterior myoepithelium, Posterior pigmented epithelium
At which of the following iris locations does the anterior myoepithelium lack muscular processes?
Near the pupillary margin
Which 2 of the following iris layers is responsible for iris color?
Anterior border layer, iris stroma
Heterochromia can be congenital or due to uveal inflammation
-If congenital, damage to the sympathetic innervation to the iris may be suspected, since sympathetic fibers stimulate melanin production by the iris melanocytes and the absence of sympathetic innervation leads to the following ocular signs…
A lighter colored iris on the involved side along with ptosis and miosis
Phenylephrine/Tropicamide
Phenylephrine (sympathetic agonist) stimulates the dilator (sympathetic innervation)
Tropicamide (parasympathetic antagonist)
inhibits the sphincter (parasympathetic innervation)
Posterior synechia is an adhesion between which 2 of the following structures?
Posterior iris, anterior lens
What part of the iris is thickest? Thinnest?
The iris root is the thinnest part of the iris, being only 0.5 mm thick and therefore prone to tearing following trauma to the eye.
The collarette is the thickest part of the iris.
What are the 4 layers of the iris? State which layers of the iris contain an epithelium and classify the epithelial type(s)
(A->P)
- ANTERIOR BORDER LAYER - thin condensation of the iris stroma (fibroblasts and melanocytes) NOT covered by an epithelium
- fibroblasts form discontinuous sheet of flat, stellate cells from iris root to pupil (cells connected by gap junctions + intermediate junctions)
- melanocytes lie deep to fibroblasts and absorb light
- absent in crypts of Fuchs; extends into anterior chamber angle as iris processes attached to TM. - IRIS STROMA - loose CT (sphincter pupillae muscle lies within the stroma + nerve fibers LPCN/SPCN
- highly vascular; with collagen fibers, fibroblasts, melanocytes, mast cells, clump cells and glycosaminoglycans (forming the extensive ground substance
- The iris stroma is continuous with the ciliary body stroma at the iris root! - ANTERIOR MYOEPITHELIUM - (the cytoplasm in the basal portion of the anterior myoepithelial cells
contains myofilaments of the dilator pupillae muscle)
-single layer of cuboidal cells
-the bases of the anterior myoepithelial cells face the iris stroma
-apical part adjacent to posterior pigmented epithelium (contains nuclei, cytoplasm, organelles, melanin pigment granules)
-basal part face iris stroma and form muscular processes (mitochondrion and myofilaments) - POSTERIOR PIGMENTED EPITHELIUM -
- single layer of columnar cells
- the bases of the posterior pigmented epithelial cells face the posterior chamber
- apex faces apex of anterior myoepithelium (covered with microvilli)
- base (containing nucleus) faces posterior chamber
3/4 cover posterior surface of the iris
What is missing at the crypts of Fuchs and what is the significance of that?
The anterior border layer is missing at the crypts of Fuch. These crypts allow aqueous humor entrance and exit into the spaces of the iris stroma as the pupil dilates and constricts.
Minor arterial circle of the iris is formed by these blood vessels:
Is this a complete or incomplete circle?
Two long posterior ciliary arteries and the
seven anterior ciliary arteries -> major arterial circle-> branches off while going through iris stroma/collaratte to form second circle: minor arterial circle
The minor arterial circle lies beneath the collarette and is an “incomplete” ring that branches of the minor arterial circle run radially inward through the iris stroma to the pupil margin (thus lying in the pupillary zone of the iris)
Define the following clinical terms:
- Iridodialysis
- Posterior synechia
- Peripheral anterior synechia (PAS)
- Iridodenesis
- Anterior synechia
- Iris sphincter tear (include where it occurs and what lead to it happening)
IRIDODIALYSIS
the clinical term used for when the iris root is tearing away from the anterior surface of the ciliary body after blunt trauma to the eye or head (blood vessels & nerves of the iris can be torn or damaged, leading to blood vessels bleeding into the anterior or posterior chamber or both and paralysis of the muscles of the iris in the section(s) of the iris where nerves have been damaged)
POSTERIOR SYNECHIA
an adhesion between the posterior surface of the iris & anterior lens surface
-Use of drugs to dilate the pupil will usually break a posterior synechia. The break usually occurs between the 2 posterior epithelial layers of the iris leaving remnants of the posterior pigmented epithelium on the anterior surface of the lens.
PERIPHERAL ANTERIOR SYNECHIA (PAS)
adhesion between anterior surface of iris at the periphery of the iris that blocks the trabecular meshwork (TM) and may impede aqueous outflow if it blocks a considerable amount of the TM, leading to an increase in intraocular pressure (IOP) because aqueous humor is prevented from leaving the anterior chamber
IRIDODONESIS tremulousness (quiver, wobble or jiggle) of the iris especially after the removal of the lens or if the lens is sub-luxed or dislocated. The iris no longer has the “back support” the lens used to provide, so the iris trembles or quivers as the eye moves.
ANTERIOR SYNECHIA
an adhesion between the anterior surface of the iris & corneal endothelium
IRIS SPHINCTER TEAR
pupil margin appears irregular & serrated (or notched) where the tears have occurred; can lead to tearing of sphincter pupillae fibers and inability to fully constrict
-blunt trauma to the eye/head
The major arterial circle of the iris is located here: _________ and its branches in the iris lie specifically here (i.e. zone(s), layer of the iris):
_____________
located in the ciliary body
branches in the iris run radially through iris stroma as iris blood vessels (in ciliary zone of iris) and at collarette, anastomosing to form minor circle
Where are zonula occludens junctions located in the iris? Be specific. Where are gap junctions are located in the iris epithelia?
ZONULA OCCLUDENS
- endothelial cells of iris capillaries (continuous)
- posterior pigmented epithelium cells are joined at apical-lateral borders by junctional complexes composed of zonula occludens, adherens, gap junctions
GAP JUNCTIONS
- anterior myoepithelial cells, intercellular junctions between anterior/posterior epithelia
- anterior border layer
- dilator processes make gap junctions with one another
Describe why cells and proteins can enter the anterior chamber if someone has a uveitis and the source of the cells and proteins. What types of cells are seen?
If the zonula occludens junctions are damaged as in iritis or uveitis, proteins and/or blood cells leak into the aqueous humor creating the clinical signs of “cells & flare” in the anterior chamber.
Cells = blood cells (RBCs and/or WBCs)
Flare = protein