OCULAR ANATOMY > THE IRIS > Flashcards
THE IRIS Flashcards
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
What mainly determines iris color?
In all colored irises (blue, gray, green, brown) the two epithelial layers of the iris are heavily pigmented and all colored irises have the same number of melanocytes in their anterior border layer and iris stroma. Therefore iris color seems to mainly be determined by the amount of pigment.
Brown irises have large amounts of melanin pigment in their stromal & anterior border layer melanocytes. Blue irises have less melanin pigment in their stromal & anterior border layer melanocytes.
Describe why someone could be born with 2 different colored irises (1 light and 1 dark). What is this condition called? What other symptoms would they have?
Heterochromia is a difference in coloration between the two irises or portions of one iris differ in color from the rest of the iris due to:
- an irregular distribution of the melanocytes
- lack of melanin production by the melanocytes
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: lighter colored iris on involved side, ptosis, miosis
What do zonula occludens junctions of posterior pigmented epilthelium of iris help prevent?
Adjacent posterior pigmented epithelial cells (PPE) are joined at their apical-lateral borders by junctional complexes composed of zonula occludens, zonula adherens and gap junctions.
The junctional complex prevents diffusion of substances (such as proteins) into the posterior chamber from either the iris stroma or anterior chamber.
What is the difference between the pupil margin and the pupillary ruff?
Pupillary ruff is a dark brown band found at the pupillary margin and is the anterior extension of the two pigmented epithelial layers that line the posterior surface of the iris. The pupillary ruff gives the pupillary margin a corrugated appearance & it gives the pupil a dark brown border.
Which cells do gap junctions found in the epithelia on the posterior surface of the iris interconnect?
Gap junctions found in the epithelia on the posterior surface of the iris interconnected the anterior and posterior epithelia.
Which cells do desmosomes found in the epithelia on the posterior surface of the iris interconnect?
Posterior epithelial cells are also joined by one or more desmosomes
What is the clinical significance of lack of an epithelium on the anterior surface of the iris?
Thus, aqueous humor in the anterior chamber freely permeates the iris surface and enters the underlying stroma.
(CO) 1. Name the part or region of the iris where it is thinnest and thickest
see previous question
(CO) 2. Describe the parts of the iris as seen on anterior surface and posterior surface including
the anatomical location on the iris or diagram of the iris (anterior view or in a section), what they are, etc where applicable. Be sure to include:
-pupil margin
-iris root- including its location & what it attaches to
-collarette and what lies beneath it
-trabeculae
-crypts of Fuchs and what they are, what layer of the iris is missing there and why the iris has them (related to aqueous humor)
-pupillary ruff and what forms it
-contraction furrows on anterior surface of iris and what causes them
-ciliary zone and what structures are found in it
-pupillary zone and what structures are found in it
-iris nevus (freckle)- what causes it?
see previous question
IRIS ROOT
Stroma of the iris is continuous with the ciliary body stroma at the iris root. Plasma-derived proteins in the ciliary body stroma not released into the posterior chamber can freely diffuse into the iris stroma via the iris root, accumulate there and then be released into the aqueous humor of the anterior chamber.
COLLARETTE
separates pupillary and ciliary zones of iris
TRABECULAE
Trabeculae are radially oriented branching collagenous beams seen on the anterior surface of the iris. They enclose oval-shaped, pit-like depressions called crypts of Fuchs (pupillary zone, collarette region, & at the iris periphery)
CONTRACTION FURROW
They are seen as lighter colored lines, concentric with the pupil, caused by folding of the iris as the pupil dilates. The furrows deepen as the pupil dilates.
The anterior surface of the iris is divided into two zones:
PUPILLARY ZONE (centrally located; lies adjacent to the pupil)
CILIARY ZONE (located peripherally; lies adjacent to the ciliary body)
- where contraction furrows are found
- the ONLY PART that thickens during pupil dilation
- myofilaments of the dilator are radially arranged in the iris and are mainly located in the ciliary zone of the iris (extend into the pupillary zone where they overlap with the sphincter pupillae muscle fibers)
IRIS NEVUS
pigmented congenital benign neoplasms (hamartomas) composed of melanocytes (buildup of melanocytes @ anterior border layer)
(CO) 3. Name all the structures located in the ciliary and pupillary zones of the iris such as:
- minor and major arterial circle of the iris and their branches?
- Sphincter pupillae muscle and dilator pupillae muscle
- Crypts of Fuchs?
- Contraction furrows?
- Pupillary ruff?
CILIARY ZONE
- crypts of Fuch’s
- anterior border layer
- dilator pupillae muscle
- iris root
- ciliary body epithelium
PUPILLARY ZONE
- crypts of Fuch’s
- anterior border layer
- sphincter pupillae muscle
- pupillary ruff
- posterior pigmented epithelium
- anterior myoepithelium
(CO) 4. Name the 4 layers of the iris from anterior to posterior
see previous question
(CO) 5. Describe the anterior border layer. Be sure to include:
- cell types
- whether a continuous or discontinuous layer
- clinical significance that it lacks an epithelium
- where the anterior border layer is absent
see previous question
(CO) 6. Describe the iris stroma including:
its continuity to the ciliary body stroma at the iris root and clinical significance
Be sure to include: connective tissue type and structures in the stroma
Describe the sphincter pupillae muscle. Include muscle type, location in the stroma, fiber
orientation, innervation and action.
Describe the blood supply to the iris. Be sure to include:
- the origin of the iris blood vessels
– the location of the major and minor arterial circles and how the circles are formed
– whether their iris blood vessels travel in straight or spiral course and why
– what layer of the iris the vessels lie in
– describe the types of capillaries found in the iris and their characteristics, why the iris
capillaries need to be this type and what happens if their zonula occludens junctions are damaged.
Name the nerves in the iris stroma. Be sure to include the course and
functions of the LPCN and SPCN, cell body locations, structures innervated
If there is blunt trauma to the eye or head, the iris root is prone to tearing away from the anterior surface of the ciliary body = iridodialysis.
iris stroma = loose connective tissue; contains smooth muscle of the iris sphincter, blood vessels & nerve fibers (LPCN & SPCN) to the iris
Sphincter pupillae = pupillary zone of iris; ring of smooth muscle around pupil. The fibers are in the iris stroma, deep to the surface and adjacent to anterior iris myoepithelium.
-postganglionic parasympathetic fibers whose cell bodies lie in the ciliary ganglion
innervate the sphincter pupillae muscle of the iris
> Major and minor arterial circles of the iris formed by the 2 LPCA and 7 ACAs. Radially running arteries in the iris stroma will follow a spiral (not straight) course towards the pupillary margin.
> The iris blood vessels have a continuous endothelium, continuous basal lamina and the endothelial cells of the iris capillaries are joined at their apico-lateral borders by zonulae occludens junctions. The zonula occludens junctions create the blood/aqueous barrier. **prevent proteins and cells in the blood from leaking into the aqueous humor of the anterior chamber.
> The iris is innervated by the long posterior ciliary nerves (LPCN) & short posterior ciliary
nerves (SPCN)
The SPCN (15-20) pierce the sclera around the optic nerve and the LPCN (2) pierce the
sclera medial and lateral to the optic nerve. The nerves run forward in the suprachoroidal space to the iris, accompanied by the corresponding
arteries (LPCA & SPCA).
> LPCN (branch of nasociliary nerve) contain:
- sensory fibers to iris, CB, cornea, bulbar conjunctiva (and their cell bodies lie in the trigeminal ganglion)
- postganglionic sympathetic fibers (whose cell bodies lie in the superior cervical sympathetic ganglion) that innervate the dilator pupillae muscle of the iris
> SPCN (from the ciliary ganglion) contain:
- sensory fibers to the iris, CB, cornea, bulbar conjunctiva whose cell bodies lie in the trigeminal ganglion
- postganglionic parasympathetic fibers whose cell bodies lie in the ciliary ganglion (innervate the sphincter pupillae muscle of the iris)
(CO) 7. Name and describe the two epithelial layers on the posterior surface of the iris
-Be sure to include the epithelial type, orientation of the cells in relation to each other as well as the iris stroma and posterior chamber
-Describe what structures are located in the apex and base of the anterior myoepithelium and posterior pigmented epithelium as discussed in class
-Describe the dilator pupillae muscle including how it is formed, location, muscle type, innervation and action.
- State which epithelial layer is a myoepithelium and why
- Be able to describe the location of the following junctions in the epithelia of the iris and their
function (i.e. between anterior myoepithelial cells & posterior pigmented epithelial cells, between adjacent anterior myoepithelial epithelial cells, between adjacent posterior pigmented epithelial cells):
Zonula occludens junctions, Desmosomes, Gap junctions
see previous question
(CO) 8. Be able to define iridodialysis, iridodenesis, anterior synechia, posterior synechia, peripheral
anterior synechia, heterochromia, iris sphincter tears and persistent pupillary membrane
IRIDODIALYSIS
blunt trauma to the eye or head, the iris root is prone to tearing away from the anterior surface of the ciliary body; 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 (sector paralysis).
IRIDODONESIS
see previous question
PERSISTENT PUPILLARY MEMBRANE
remnant of the central part of a transient embryonic vascular network to the lens that
formed between the lens & corneal endothelium during ocular development
-looks like spidery white or brown strands
that cross the pupil. It most commonly presents as a fine strand of pigmented tissue which arises from the iris collarette and attaches to another spot on the iris
-may present as one or several strands
(CO) 9. Discuss iris coloration, including:
- Major reasons for differences in iris color (brown, blue, etc)
- What mainly determines iris color
- Causes of heterochromia (congenital vs. acquired due to inflammation) and ocular signs
- Effects of sympathetic innervation on melanocytes of iris
- Effects of xalatan on iris color and mechanism of action
Sympathetic fibers stimulate melanin production by the iris melanocytes and the absence of sympathetic innervation leads to the following ocular signs: lighter colored iris on involved side along with ptosis and miosis.
Xalatan causes melanocytes to increase pigment synthesis
(CO) 10. Be able to state where in the iris you can find zonula occludens junctions
see previous question
