<ul>
 <li>Thin contractile circular disk</li>
 <li>Approximately 12mm diameter</li>
 <li>4 layers</li>
 <li>
 Cone-shaped: pupil margin more anterior and rests on lens (iridonesis in aphakia due to loss of
 support)
 </li>
 <li>Thickest at collarette and thinnest at insertion into ciliary body</li>
</ul>
## Embryology
<ul>
 <li>Develops from 14 weeks</li>
 <li>Neuroectoderm: iris epithelium and muscles (unique)</li>
 <li>Mesenchyme: stroma, tunica vaculosa lentis and pupillary membrane vessels</li>
 <li>Long posterior ciliary and anterior ciliary arteries infiltrate</li>
 <li>Pupillary membrane disappears at 6 months</li>
 <li>Sphincter muscle develops first (14 weeks), then dilator (6 months)</li>
 <ul>
 <li>
 Note: the dilator pupillae never fully separates from the anterior epithelium and is therefore
 always partly modified basal processes of these neuroepithelial cells
 </li>
 </ul>
 <li>
 Posterior epithelium is initially amelanotic but becomes highly pigmented from centre outwards
 by 7-8 months. Simultaneously the anterior layer loses its pigment
 </li>
</ul>
<ClinicalCorrelate>
 
 Melanocyte migration to produce the pigmentation of the posterior iris epithelium is stimulated
 by sympathetic innervation, hence a pale iris is seen in congenital Horner&rsquo;s syndrome.
 
</ClinicalCorrelate>
## Anterior border layer
<ul>
 <li>Thickened stroma with fibroblasts and melanocytes</li>
 <li>Deficient in areas creating crypts so that stroma is in contact with AC</li>
</ul>
## Stroma
<ul>
 <li>Connective tissue</li>
 <li>
 Fibroblasts, melanocytes (which provide colour), collagen fibres (types 1 and 3), macrophages
 </li>
 <li>Clumps of macrophages (clumps of Koganei)</li>
 <li>Sphincter muscle lies within stroma at pupillary zone between collarette and margin.</li>
 <ul>
 <li>Concentrically arranged</li>
 </ul>
</ul>
## Dilator muscle
<ul>
 <li>Derived from anterior iris epithelium: basal processes rest in this layer</li>
 <li>Occupies peripheral ciliary zone outside collarette</li>
 <li>Radially arranged</li>
 <li>Sympathetic activity controlled by alpha receptors</li>
</ul>
## Anterior iris epithelium
<ul>
 <li>In contact with the anteriorly positioned stroma</li>
 <li>Few melanin granules situated in the apical cytoplasm</li>
 <li>Continuous with the outer pigmented ciliary epithelium</li>
</ul>
## Posterior iris epithelium
<ul>
 <li>Cuboidal and larger than the anterior layer</li>
 <li>
 Becomes heavily pigmented (contains melanin): although continuous with inner, non-pigmented
 ciliary epithelium and thence with the neuroretina
 </li>
 <li>Apices of this epithelium oppose the apices of the myoepithelial cells</li>
 <ul>
 <li>
 This double layer of epithelial provides the main blood-aqueous barrier
 </li>
 </ul>
 <li>Extends anteriorly to form ruff</li>
</ul>
## Blood supply
<ul>
 <li>Major circle of iris lies in iris root:&nbsp;</li>
 <ul>
 <li>Comprises anastomoses between long posterior and anterior ciliary arteries</li>
 </ul>
 <li>Branches extend concentrically</li>
 <li>Minor circle formed at collarette</li>
 <li>
 Capillaries characterised by numerous tight junctions (zonula occludens), non-fenestrated and
 with a thickened basal lamina and so do not leak (eg fluorescein): contribute{' '}
 blood-aqueous barrier
 </li>
 <li>
 Note: capillaries in ciliary body do not have tight junctions but the barrier is instead
 maintained by the tight junctions in the ciliary epithelium
 </li>
</ul>
## Nerve supply
<ul>
 <li>
 Parasympathetic supply to ciliary body and sphincter pupillae via short ciliary nerves from
 ciliary ganglion (oculomotor nerve)
 </li>
 <ul>
 <li>Preganglionic fibres come from Edinger-Westphal nucleus</li>
 </ul>
 <li>
 Sympathetic supply joins sensory fibres in the long ciliary nerves (branch from nasociliary of
 ophthalmic nerve). Preganglionic fibres from superior sympathetic chain.
 </li>
 <ul>
 <li>
 Post-ganglionic fibres from superior cervical ganglion travel along internal carotid plexus to
 long ciliary nerves.
 </li>
 </ul>
</ul>

AC to Lens

Iris

Intro

FRCOphth Part 1 Study Notes

Orbit and ocular adnexae

Orbit

Extraocular Muscles

Orbital Blood Vessels

Paranasal Sinuses

Lacrimal Glands

Tear Film

Eyelids

Blinking

Anterior segment - ocular surface

Conjunctiva

Conjunctivitis

Sclera

Cornea

Corneal Structure And Development

Corneal Physiology

Angle

Ciliary Body

Aqueous Humour Dynamics

Pupil

Lens

Posterior segment

Choroid

Vitreous

Retinal Macrostructure

Neurosensory Retina

Retinal Pigment Epithelium

Neuroanatomy

Venous Sinuses

Cerebral Ventricles

Cerebral Blood Supply

Supranuclear Gaze Pathways

Head And Neck Autonomic Nervous Supply

Head And Neck Glands

Osteology

Nerves

Muscles And Pharyngeal Arches

Extraocular Nerves

Sensory Nerves

Physiology

Physics Of Blood Flow

Neuronal Control Of Blood Vessels

Oxygen-Haemoglobin Dissociation Curve

Cytochrome p450

Pituitary Gland

Thyroid Hormone Production

Insulin

Glucagon

Parathyroid Hormone

Corticosteroids

Catecholamines

Cardiac Cycle

Renal Physiology

Fluid Balance

Acid-Base Balance

Muscle Physiology

Sensory Fibres

Cutaneous Receptors

Endocytosis

Glycosaminoglycans

Condensed Ocular Biochemistry

Eye Movements

Accomodation

Vision

Visual Cycle And Phototransuction

Visual Pathway

Visual Acuity

Colour Vision

Binocular Vision

Pathology

Collagen

Tissue Damage

Inflammation

Disease Entities

Wound Healing

Thrombosis / Atherosclerosis

Cell Growth

Neoplasia

Histopathology

Nystagmus

Free Radicals And Antioxidants

Immunology

Ocular Immunology

Microbiology

Viral Infections

Bacterial Infections

Fungal Infections

Protozoa

Nematodes

Antimicrobials

Genetics

Chromosomes

Mitosis

Meiosis

Genes

Polypeptide Synthesis

Histones

MicroRNA

Hardy-Weinberg Equilibrium

Mutations

Chromosome Defects

Autosomal Inheritance

X-Linked Inheritance

Mitochondrial Inheritance

Multifactorial Inheritance