Iris Flashcards
what is the function of the iris
it acts as a mobile diaphragm separating the aqueous compartment into anterior and posterior chambers
what is the normal size of the iris
1-8mm
why does the iris change size (not the pupil)
it regulates the amount of light entering/illuminating the retina
what is the average diameter of the iris
12mm
where is the iris the thickest
at the iris collarette (0.6mm thick)
where is the iris collarette located
1.5mm from the pupillary margin
where is the iris the thinest
near its insertion into the ciliary body, the root of the iris (0.5mm thick)
what does the iris collarette separate
it is a circular ridge that separates the iris into a pupillary zone and a ciliary zone
what determines the iris color
it is due to stromal absorption, whatever light waves are not absorbed are reflected back and that is the eye color
if the iris was blue, what wavelengths would be absorbed
the longer wavelengths, allowing shorter (blue) to be reflected back
what is the pupillary ruff
where the pupillary zone starts
what are fuch’s crypts
depressions on the anterior surface of the iris, along the collarette
what are the radial ridges
formed by the underlying stromal vasculature in the ciliary region that can be seen
how is the posterior side of the iris different from the anterior side
it is more smooth and uniform
how many layers does the iris have
5: anterior border layer, stroma, muscle layer, dilator muscle and anterior pigment epithelium, and posterior pigmented epithelium
where does the anterior border layer come from
it is a condensation of the underlying stroma
how is the collagen arranged in the anterior border layer of the iris
in radial columns appearing as white fibers in light-colored irises
what is an iris process
after the anterior border layer terminates at the iris root, the iris may extend in a spoke-like fashion at schwalbes line
what is absent in the anterior border layer
the oval shaped Fuch’s crypts
what is the collagen the most abundant in the stroma
around the blood vessels
where are the arteries derived from that supply the iris
the major circle of the iris (located in the ciliary body)
what arteries supply the MAC (major arterial circle)
2 long posterior ciliary arteries and 7 anterior ciliary arteries
where is the minor arterial circle located
near the collarette
what keeps the blood vessels from kinking during mydriasis and miosis
collagen fibers that surround and anchor the blood vessels
where do the veins drain for the iris
into the vortex veins
are iris capillaries fenestrated or nonfenestrated
they are non-fenestrated
how are the iris stroma endothelial cells joined together
by zonula occludens (tight junctions) to form the blood-aqueous barrier
what is the iris freely permeable to
aqueous humor
where is the sphincter muscle located
within the stroma
what type of muscle is the sphincter muscle
spindle-shaped smooth muscle cells joined by gap junctions
what shape is the sphincter muscle
it is circular, within the pupillary zone of the iris
how wide is the sphincter muscle
about 0.75-0.1mm wide
does the sphincter muscle remain functional if it is severed
yes
if the sphincter muscle contracts, what happens to the pupil
it will constrict (miosis)
what innervates the sphincter muscle
postgagnlionic parasympathetic fibers from the short posterior ciliary nerves
what layer is posterior to the iris stroma
the myoepithelial layer: 2 portions- muscular basal portion and the epithelial apical portion
where is the muscular portion of the myoepithelial layer
adjacent to the stroma- make up the iris dilator muscle
how is the dilator muscle arranged
it starts from the iris root and extends radially toward the pupil, overlapping manor
what happens when the dilator muscle contracts
the pupil will dilate
what innervates the dilator muscle
long posterior ciliary nerves (nasociliary branch of ophthalmic, trigeminal nerve 5)
what signals do the nerves carry to the dilator muscle
postganglionic sympathetic innervation from the superior ganglion
is the pupil maintain a constant size
no it is always in hippus, due to struggle between the sympathetics and parasympathetic innervation
why do you think LSD for the dilator muscle
Long, sympathetic, Dilator
how does the anterior pigmented iris epithelium face the posterior pigmented epithelium
apex to apex
how are the twwo pigemented epithelial layers connected
via tight intercellular junctions and desmosomes
which layer of pigemented epithelium is move heavily pigmented
the posterior pigment epithelium
what type of cells are the anterior pigement epithelium
they are cuboidal shaped
what type of cells are the posteior pigement epithelium
columnar shaped
why does the posterior pigmented epithelium have tight junctions and desmosomes
prevent macromolecules from entering the posterior chamber from the anterior chamber
Does the posterior or anterior pigmented epithelium lose its pigment
the posterior does as it becomes the NPE of the ciliary body
does the posterior pigmented epithelium have a basement membrane
yes, it covers the basal side of the cell, giving the posterior chamber a lining
how does the iris get blood supply
by 2 long posterior ciliary arteries and the 7 short anterior ciliary arteries
what do the 2 long posterior ciliary arteries and the 7 short anterior ciliary arteries merge to form
the MAC
is the MAC a plexus
yes, not a single vessel
what are the “Thick Walled Vessels”
the arteries that extend out radially from the MAC towards the pupillary margin, lined with collagen
