Iris

Question 1

what is the function of the iris

Answer 1

it acts as a mobile diaphragm separating the aqueous compartment into anterior and posterior chambers

Question 2

what is the normal size of the iris

Answer 2

1-8mm

Question 3

why does the iris change size (not the pupil)

Answer 3

it regulates the amount of light entering/illuminating the retina

Question 4

what is the average diameter of the iris

Answer 4

12mm

Question 5

where is the iris the thickest

Answer 5

at the iris collarette (0.6mm thick)

Question 6

where is the iris collarette located

Answer 6

1.5mm from the pupillary margin

Question 7

where is the iris the thinest

Answer 7

near its insertion into the ciliary body, the root of the iris (0.5mm thick)

Question 8

what does the iris collarette separate

Answer 8

it is a circular ridge that separates the iris into a pupillary zone and a ciliary zone

Question 9

what determines the iris color

Answer 9

it is due to stromal absorption, whatever light waves are not absorbed are reflected back and that is the eye color

Question 10

if the iris was blue, what wavelengths would be absorbed

Answer 10

the longer wavelengths, allowing shorter (blue) to be reflected back

Question 11

what is the pupillary ruff

Answer 11

where the pupillary zone starts

Question 12

what are fuch’s crypts

Answer 12

depressions on the anterior surface of the iris, along the collarette

Question 13

what are the radial ridges

Answer 13

formed by the underlying stromal vasculature in the ciliary region that can be seen

Question 14

how is the posterior side of the iris different from the anterior side

Answer 14

it is more smooth and uniform

Question 15

how many layers does the iris have

Answer 15

5: anterior border layer, stroma, muscle layer, dilator muscle and anterior pigment epithelium, and posterior pigmented epithelium

Question 16

where does the anterior border layer come from

Answer 16

it is a condensation of the underlying stroma

Question 17

how is the collagen arranged in the anterior border layer of the iris

Answer 17

in radial columns appearing as white fibers in light-colored irises

Question 18

what is an iris process

Answer 18

after the anterior border layer terminates at the iris root, the iris may extend in a spoke-like fashion at schwalbes line

Question 19

what is absent in the anterior border layer

Answer 19

the oval shaped Fuch’s crypts

Question 20

what is the collagen the most abundant in the stroma

Answer 20

around the blood vessels

Question 21

where are the arteries derived from that supply the iris

Answer 21

the major circle of the iris (located in the ciliary body)

Question 22

what arteries supply the MAC (major arterial circle)

Answer 22

2 long posterior ciliary arteries and 7 anterior ciliary arteries

Question 23

where is the minor arterial circle located

Answer 23

near the collarette

Question 24

what keeps the blood vessels from kinking during mydriasis and miosis

Answer 24

collagen fibers that surround and anchor the blood vessels

Question 25

where do the veins drain for the iris

Answer 25

into the vortex veins

Question 26

are iris capillaries fenestrated or nonfenestrated

Answer 26

they are non-fenestrated

Question 27

how are the iris stroma endothelial cells joined together

Answer 27

by zonula occludens (tight junctions) to form the blood-aqueous barrier

Question 28

what is the iris freely permeable to

Answer 28

aqueous humor

Question 29

where is the sphincter muscle located

Answer 29

within the stroma

Question 30

what type of muscle is the sphincter muscle

Answer 30

spindle-shaped smooth muscle cells joined by gap junctions

Question 31

what shape is the sphincter muscle

Answer 31

it is circular, within the pupillary zone of the iris

Question 32

how wide is the sphincter muscle

Answer 32

about 0.75-0.1mm wide

Question 33

does the sphincter muscle remain functional if it is severed

Answer 33

yes

Question 34

if the sphincter muscle contracts, what happens to the pupil

Answer 34

it will constrict (miosis)

Question 35

what innervates the sphincter muscle

Answer 35

postgagnlionic parasympathetic fibers from the short posterior ciliary nerves

Question 36

what layer is posterior to the iris stroma

Answer 36

the myoepithelial layer: 2 portions- muscular basal portion and the epithelial apical portion

Question 37

where is the muscular portion of the myoepithelial layer

Answer 37

adjacent to the stroma- make up the iris dilator muscle

Question 38

how is the dilator muscle arranged

Answer 38

it starts from the iris root and extends radially toward the pupil, overlapping manor

Question 39

what happens when the dilator muscle contracts

Answer 39

the pupil will dilate

Question 40

what innervates the dilator muscle

Answer 40

long posterior ciliary nerves (nasociliary branch of ophthalmic, trigeminal nerve 5)

Question 41

what signals do the nerves carry to the dilator muscle

Answer 41

postganglionic sympathetic innervation from the superior ganglion

Question 42

is the pupil maintain a constant size

Answer 42

no it is always in hippus, due to struggle between the sympathetics and parasympathetic innervation

Question 43

why do you think LSD for the dilator muscle

Answer 43

Long, sympathetic, Dilator

Question 44

how does the anterior pigmented iris epithelium face the posterior pigmented epithelium

Answer 44

apex to apex

Question 45

how are the twwo pigemented epithelial layers connected

Answer 45

via tight intercellular junctions and desmosomes

Question 46

which layer of pigemented epithelium is move heavily pigmented

Answer 46

the posterior pigment epithelium

Question 47

what type of cells are the anterior pigement epithelium

Answer 47

they are cuboidal shaped

Question 48

what type of cells are the posteior pigement epithelium

Answer 48

columnar shaped

Question 49

why does the posterior pigmented epithelium have tight junctions and desmosomes

Answer 49

prevent macromolecules from entering the posterior chamber from the anterior chamber

Question 50

Does the posterior or anterior pigmented epithelium lose its pigment

Answer 50

the posterior does as it becomes the NPE of the ciliary body

Question 51

does the posterior pigmented epithelium have a basement membrane

Answer 51

yes, it covers the basal side of the cell, giving the posterior chamber a lining

Question 52

how does the iris get blood supply

Answer 52

by 2 long posterior ciliary arteries and the 7 short anterior ciliary arteries

Question 53

what do the 2 long posterior ciliary arteries and the 7 short anterior ciliary arteries merge to form

Answer 53

the MAC

Question 54

is the MAC a plexus

Answer 54

yes, not a single vessel

Question 55

what are the "Thick Walled Vessels"

Answer 55

the arteries that extend out radially from the MAC towards the pupillary margin, lined with collagen