Iris

Question 1

What is iris

Answer 1

Thin contractile pigment diaphragm within a central aperture eg pupil forms division between anterior and posterior Chamber
Controls amount of light reaching the retina
suspended in aqueous humour
Attached to ciliary body at iris root

Question 2

Dimensions of iris

Answer 2

Thickest at colarette- 0.6mm , 0.1mm at where meets CB
Colarette divides into two zones pupillary and ciliary regions
From colarette back to iris root is ciliary region
From colarette to pupil is pupillary region

Question 3

Pupil

Answer 3

diameter from 1mm to 8mm
Dilation - Mydriasis
Constriction- Miosis
Change in length of iris consequently size of pupil is all carried out by ciliary region

Question 4

Iris colour

Answer 4

Due to pigmentation on anterior surface
More pigmentation eg more melanin = browner iris and underlying structure is hidden
Little or no pigmentation= blue as scattering of light in stroma as seen at birth
Colour is inherited brown being dominant and blue recessive
Different eye colours- heterochromia

Question 5

Anterior Border layer - 1

Answer 5

Contains two cell types- melanocytes and fibroblasts
Contains fuchs crypts
FUCH CRYPTS- gaps on anterior surface that allow aqueous humour to acmes the tissues of stroma of iris

Question 6

Stroma - 2

Answer 6

Collagenous connective tissue, melanocytes, fibroblasts
Contains blood vessels and sphincter muscle
Sphincter muscle- in extreme mitosis whole muscle can be reduced to 15% of original length

Question 7

Epithelium- 3

Answer 7

Double epithelial layer deeply pigmented
Beyond the sphincter the deeper layer carries contractile processes which form dilators muscles
-Anterior epithelial cells have dilator processes
- Posterior epithelial cells densely packed with melanin prohibits passage of light
Contains PUPILLARY RUFF- the deeply pigmented epithelium extends beyond tip of iris which is visible around pupil

Question 8

Blood supply

Answer 8

Radial blood vessels have spiral course means they can grow longer and shorter depending on state of mydriasis or miosis .
Arteries derived from Major Arterial Circle
MAC is within ciliary body and runs through iris and joins again in minor iridium circle at level of colarette
Blood vessels also use this as exchange of metabolites and waste products of aqueous

Question 9

Nerve supply

Answer 9

Sensory nerves are only found in iris root
Sphincter has parasympathetic innervation- mitosis from 3rd cranial Neve
Dilator has sympathetic innervation- mydriasis superior cervical ganglion