IRIS

Question 1

UVEA STRUCTURES

Answer 1

• iris
• ciliary body
• choroid

Question 2

UVEA

Answer 2

• vascular layer of eye
• between sclera + retina
• made up of BV’s in a loose network of connective tissue + pigment cells
• BV’s provide circulation to eye
• pigment prevents unwanted light entering eye + reduces light reflections

Question 3

IRIS STRUCTURE

Answer 3

thin contractile pigmented diaphragm with central aperture (pupil)

Question 4

IRIS FUNCTIONS

Answer 4

• controls amount of light reaching retina
• depth of focus
• reduces aberrations
• forms division between anterior + posterior chambers
• suspended in aqueous humour between cornea + lens
• attached to ciliary body at iris root

Question 5

PUPIL

Answer 5

• not located centrally
• displaced slightly down + in
• width of the ciliary region alters the most, the pupillary zone remains almost constant

Question 6

MYDRIASIS

Answer 6

dilation of pupil

Question 7

MIOSIS

Answer 7

constriction of pupil

Question 8

IRIS COLOUR

Answer 8

• depends on pigmentation of ant. surface
• more pigmentation -> browner iris + more underlying structure is hidden
• little/ no pigment -> blue, as scattering of light in stroma

Question 9

HETEROCHROMIA

Answer 9

large variations between colours of eye

Question 10

ANISOCORIA

Answer 10

unequal size of pupils

Question 11

IRIS LAYERS

Answer 11

1. anterior border layer
2. stroma
3. epithelium

Question 12

ANTERIOR BORDER LAYER (outer)

Answer 12

• dense covering
• melanocytes (contain granules of pigment melanin)
• fibroblasts + collagen fibres
• no epithelium

Question 13

CRYPTS

Answer 13

allow aqueous humour to access tissues of the iris

Question 14

STROMA

Answer 14

• collagenous
• connective tissue containing fibroblasts + pigment cells in a mucopolysaccharide matrix
• iris blood vessels + sphincter muscle contained here

Question 15

SPHINCTER PUPILLAE MUSCLE

Answer 15

• band of smooth muscle
• runs parallel to pupil margin
• in extreme miosis the whole muscle can be reduced to 15%

Question 16

EPITHELIUM

Answer 16

• double epithelial layer
• from pupil margin to peripheral edge of iris sphincter
• deeply pigmented
• deeper layer carries contractile processes

Question 17

POSTERIOR EPITHELIUM CELLS

Answer 17

forms the posterior pigment epithelium + densely packed with melanin

Question 18

ANTERIOR EPITHELIAL CELLS

Answer 18

have dilator processes that form the basal part of cell + an apical part that contains the nucleus + pigment granules

Question 19

IRIS MUSCLES

Answer 19

muscles work antagonistically to control pupil size

Question 20

IRIS BLOOD SUPPLY

Answer 20

• radial blood vessels enable movement during mydriasis + miosis
• arteries derived from major arterial circle (MAC) situated in ciliary body
• run through iris to anastomose in minor iridic circle

Question 21

SENSORY NERVES

Answer 21

found only in the iris root

Question 22

SPHINCTER INNERVATION

Answer 22

parasympathetic (miosis) from occulomotor nerve

Question 23

DILATOR INNERVATION

Answer 23

sympathetic (mydriasis) from cells in superior cervical ganglion

Question 24

COLLARETTE

Answer 24

divides the anterior surface into 2 zones:

• pupillary
• ciliary

Question 25

PUPILLARY RUFF

Answer 25

deeply pigmented epithelium extends beyond tip of iris