Test 1 Iris and Pupil

major role of the iris

dynamically react to ambient lighting conditions to adjust retinal illumination, plays a role in the accommodative reflex

further away from

the focal point of an infinite object is (closer to/further away from) the lens than the focal point of a real object

blur circles

occur when the image point is not on the retina

aperture stop

hole limiting the amount of light in an optical pathway placed near or at the lens, does not greatly impact the field of view

field stop 

hole placed a distance from the lens that limits the field of view, but does not greatly impact the amount of light. 

depth of field

object distance range where an acceptable focus can be achieved

depth of focus

corresponding range of image distance inside the eye where the focus is acceptable

decreasing 

(decreasing/increasing) pupil size increases depth of field and focus, and decreases aberrations 

diffraction

bending of light rays at the edge of aperture

spherical aberration

changing focal points for light rays entering off-axis in a lens (forward/back) causing a blurry image

chromatic aberration

light of different wavelengths is refracted differently by the lens so focal points vary by color

1.13 times larger, 0.55 mm in front of real

entrance pupil measurements (different because the cornea refracts the real pupil)

1.03 times larger, 0.8 mm behind real

exit pupil measurements (different because lens refracts the real pupil)

10,000

what the retina sees with a 100,000 fold change in lighting

near response triad

increased curvature of lens (accommodation, ciliary contracts), convergence, and pupil constriction

anisoconia

difference in pupil size between left and right, can also be decentered 

arcus senilis

arc of white/grey around the outer iris, may indicate systemic hyperlipidemia

anterior border layer, stroma, muscle layer (sphincter/dilator), anterior iris epithelium layer, posterior iris epithelium layer

layers of the iris

iris attachment site 

weakest area of tissue, fibrils attached to trabecular meshwork and scleral spur 

colarette

anatomical border, thickest region of the iris, divides pupillary and ciliary sections of the iris

pupillary region of iris

thicker central region with sphincter muscle

ciliary region of iris

region that contains the dilator muscle and iris root

internal carotid → opthalmic → posterior ciliary artery (long and short) + muscular artery→ anterior ciliary/forms scleral circle → intramuscular circle → major arterial circle → minor arterial circle

blood flow to iris

minor arterial circle

blood supply for the iris derived from major arterial circle formed by anatosomes of anterior ciliary arteries and long posterior ciliary arteries (LPCAs), at collarette (2/3 of the way from root to pupil)

anterior border layer 

melanocytes beneath fibroblasts concentrated on the surface, lots of holes, presents color 

crypts of fuchs 

holes that allow aqueous to enter the stroma, folds in iris from dilation can block the anterior chamber and increase IOP

1st pigmented layer

blocks light and allows iris to serve as an aperture stop

iris stroma

spongy mixture of melanocytes, fibroblasts, collagen, and blood vessels

clump cells

located in the stroma in the vicinity of the sphincter muscle, clean up spilled melanocytes and pigmented epithelium 

synerchiae

adherence of iris to lens or cornea

tight junctions/zonule occludens, overlapping endothelium and secondary covering of pericytes and collagen (to help fold like curtain)

similarities between retinal and iris blood vessels, function

sphincter

muscle layer in pupillary region that defines the collarette with the minor arterial circle of the iris

dilator

part of muscle layer that defines ciliary region (very thin)

anterior epithelium

flatter and less pigmented layer of the epithelium, forms dilator in myoepithelium 

posterior epithelium

heavily pigmented layer of epithelium, most of central tissue wraps around the pupil margin forming the pupillary ruff, columnar heavy pigmentation tight junctions, different from anterior border layer

parasympathetic innervation (ACh stimulates muscarinic receptors)

stimulates sphincter to decrease pupil size

sympathetic innervation (norepi stimulates alpha adrenergic receptors)

stimulates dilator to increase pupil size (mydriasis) (and possibly closes beta adrenergic channels on sphincter but unknown)

agonists

mimic neurotransmitter

antagonist

blocks transmitter function

G-protein second messenger and depolarization or hyperpolarization response

all autonomic NS actions require