function of iris?
regulates amt of light by pupil size
reduce light scatter
helps abberation control
increase depth of focus
Describe the layers of the iris
12mm
Anterior border:
2 zones- seperated by collarette
No epi, velvet appearence
trabeculae of conective tissue, radial arrangment- gaps=Crpts of Fuch
radial ridges = bld vessels
outer ciliary region has contraction furrows
Stroma
-no epi
-has fibroblasts (connective tissue), melanocytes (pigment), collagen (connective tissue), macrophages (immunity)
-2msc: Sphincter pupillae and Dilator pupillae
Sphincter: in pupilllary zone
circumferential ring of fibres - contraction constrict pupil)
parasym- short cil nerves, oculomotor nerve
Dilator: from root to sphincter pup
radial arrangment- constraction dilates pupil
sympathetic innervation - long cil nerves, superior cervical ganglion
Pigmented epi
2 layers: ant and post
fluid btwn=cyst
Describe the posterior iris
Black- can extend around pup margin= pupil ruff
Pig = reduce light scatter in eye
pupillary zone has radial fold
ciliary zone has circular folds
What are the 2 light absorbing molecules in iris and which one is responsible for iris pigmentation?
Hb & melanin( melanocytes and pig epi)
amt of melanin responsible : high mel= brown iris, low mel= blue iris
2 ways that heterochromia and abesence of pig occurs and each of their causes
Heterochromia
congenital
acquired- melanoma/ pharmacologically (latanoprost)
Absence of pig
congenital- albinism (pale irides and server photophobia)
acquired: pig dispersion syndrome/ trauma
describe pigment dispersion syndrome
caused by mechanical rubbing of post pig layer against lens by dilation/constriction
leads to iris transillumination- red reflex is visble
pig granules deposit on ant surface of lens blocking trab meshwork
iop increase= secondary pigmentary glaucoma
describe vasculature of iris?
major arterial circle ( 2 LPCA + 7 ACA)
minor arterial circle at pupil margin
veous drainage in varicose veins
vessels have non fenestrated endo; tight junc so low perm
x elastic lamina- bld ocular barrier
what is synechiae and describe the 2 types
when iris adheres to structures- during inflammation cells are sticky
Anterior syn
iris strands pushed to structures in angle
obstruct aq outflow, increase iop
treat surgically or pharm
Posterior syn
iris pushed to lens- x flow of aq into ant chamber
pressure build up- iris pushed forwards= iris bombe
if full extent adhesion = seclusio pupillae
treat with prolonged dilation or pupil or relaxation of lens
names of iris abnormalities
iridodyalisis- root tears away from cil body
aniridia- total absence of iris
size variation of pupil? what is uneven pupil size in each eye called? Describe 2 causes of condition.
2-4mm - bright
4-8mm - dark
smaller with age / near tasks
Anisocoria- 20% of pop
physiological: 2mm difference & no change in dim light
Aquired: sudden & neuro disease
Aperture stop vs field stop? What is the pupil?
Pupil = aperture stop
limits amt of light
doesnt prevent peripheral light
large FOV and limited amt of light
field stop- less restriction on light
prevents peripheral light entering
restricted FOV
relationship between depth of field, depth of focus and pupil diameter
DoField: tolerance in object psn without change in clarity
DoFocus: tolerance in change in image psn without change in clarity
depth of focus inverse to pupil diameter
what is hippus?
pupil constantly oscillating
2-3x/sec
rate increases in increased illum
function of pupil and describe response time
pupil - allows light to enter eye
200ms latency btwn stimulus and response:
higher light intensity= quicker rxn & greater diameter change & greater recovery time
Which are the 2 innervation pathways? which msc and cranial nerve is involved?
Parasym: sphincter, Cr. III (oculomotor)
Sym: dilator pup, symathetic nerve
Describe the parasym pathway
Describe sym pathway
What is the near vergence triad
Accommodation
Miosis ( pupil constriction)
Convergence
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