THE VASCULAR COAT OF THE EYE

ANIS SUZANNA BINTI MOHAMAD

OPTOMETRIST

WALL OF THE EYE• Fibrous (outer): sclera, cornea

• Vascular (middle): choroid, ciliary body, iris

• Nervous (inner): retina

VASCULAR TUNIC• The middle coat of eyeball a.k.a uvea

• Vascular & pigmented

• Functions:

• Regulates light entry & anchors the lens

• Absorbs reflected light

• Nourishes retina

• Components:

• Iris

• Ciliary body

• Choroid

1. IRIS

1. IRIS

• Thin, pigmented contractile circular structure

• Analogous to the diaphragm of a camera

• Lies on anterior lens surface, surrounded by aquos humor

• Extends from iris root to iris margin that forms the pupil

• The free edge is known as pupillary margin

• Separates anterior segment ant & post chambers which are continuous through pupil

• Stroma of iris is continuous with stroma of ciliary body

• Muscles: pupillary sphincter m. & pupillary dilator m.(circular) (radial)

1. IRIS

• Color depends on density of pigment & collagen in anterior limiting layer & stroma

• Heavily pigmented: brown eyes

• Lightly pigmented: lighter iris ranges from gray-blue-green

• Albino iris contains no pigment either in connective tissue cells (stroma) or in pigment layer

• Iris appears delicate pink with associated problems due to oversensitivity to light

1. IRIS

Dimensions:

• Average diameter: 12mm – varies with lighting

• Thickness: 0.5mm

• Thickest at collarette

• Collarette divides ant iris into pupillary & ciliary zones

• Thinnest at the root

• Thin regions eg iris root & margin are more susceptible to tearing in injuries

• Rough anterior surface & smooth posterior surface

1. IRIS – 4 layers

1. Anterior limiting layer

2. Stroma & sphincter muscle

3. Anterior epithelium & dilator muscle

4. Posterior epithelium

1. IRIS – 4 layers

1. Anterior border layer:

• Thin, discontinuous (cryptic)

• Composed of collagen fibrils & fibroblasts

• Underlying melanocytes

1. IRIS – 4 layers

2. Stroma & sphincter muscle

• Loose, pigmented, highly vascular connective tissue

• Pigmented epithelium lining the posterior surface

• Composed of pigmented & non-pigmented cells, collagen fibrils & extensive ground substance

• Pigmented: melanocytes & clump cells

• Non-pigmented: fibroblast, lymphocyte, macrophage, mast cells

• Amount of melanocytes in stroma determines eye color

• Sphincter muscle: lies in stroma, near pupil, concentrically arranged, contraction causes pupil constriction (miosis)

• Innervated by oculomotor, parasympathetic nervous system

1. IRIS – 4 layers

3. Anterior epithelium & dilator muscle

• Composed of unique myoepithelial cells

• Dilator muscle:

• Smooth m. which extends into stroma forming 4-5 layers

• From iris root to a point in stroma below sphincter midpoint

• Radially arranged

• Contraction causes pupil dilatation (mydriasis) –innervated by sympathetic nervous system

1. IRIS – 4 layers

4. Posterior epithelium

• Single layer of heavily pigmented simple columnar cells

• At posterior, continuous with inner non-pigmented epithelial layer of ciliary body

• Curled to anterior surface at pupil margin –pupillary ruff

• Pupillary ruff

• Pigmented epithelium

• Dilator muscle

• Circular muscle

• Blood vessels

1. IRIS – recap on pupil movement

• Mydriasis

• Pupil dilation

• Dilator pupillae m.

• Radially arranged

• Sympathetic innervation

• Conditions:

• Dark

• Fear

• Excitement

• Mydriatics?

Miosis

Pupil constriction

Sphincter pupillae m.

Circularly arranged

Parasympathetic innervation

Conditions:

Bright illumination

Sleeping

Convergence

Miotics?

• e

EYE vs CAMERA

2. CILIARY BODY

• End of choroid, connects choroid to iris circumference

• Muscular & vascular

• Functions:

• Aquous humor production (via non-pigmented epithelium)

• Control of lens accommodation (via ciliary muscles)

2. CILIARY BODY

• Anterior view: ring-shaped structure

• Sagittal view: triangular shape

• Base faces anterior chamber

• Apex at ora serrata

• 2 surfaces:

• Pars plicata: Wider anterior portion containing 70-80 ciliary processes extending into posterior chamber

• Pars plana: Flatter region extending from posterior of pars plicata to ora serrata

• k

2. CILIARY BODY

• Ora Serrata

• Transition between c.body & choroid

• Serrated pattern

• Non pigmented ciliary epithelium undergoes sharp transition to become the neural retina

• Ciliary processes

• 70-80 finger-like projections radiating from pars plicata

• Occupy peripheral part of posterior chamber

• Grooves in between serve as attachment for lens zonules

• Each process is about 2mm long and 0.5mm in diameter

2. CILIARY BODY

• 3 structures: c. muscle, c. stroma, c. epithelium

1. Ciliary muscles – 3 groups of smooth muscle fibers

• Longitudinal (outermost)

• Radial

• Circular (innermost)

2. Ciliary stroma

• Highly vascularised loose connective tissue

• Anteriorly continuous with iris stroma

• Posteriorly continuous with choroidal stroma

• Thin in pars plana

2. CILIARY BODY

3. Ciliary epithelium (innermost part of ciliary body)

• 2 layers of cells: pigmented & non-pigmented epithelial cells

1. Pigmented epithelium (outer – next to stroma)

- Anterior part continuous with anterior iris epithelium

2. Non-pigmented epithelium (inner – faces post chamber)

- Columnar cells in pars plana, cuboidal cells in pars plicata

- Anterior part continuous with posterior iris epithelium

- Produces aquous humor & glycoprotein of vitreous

- Diffusion barrier between blood & aquous

3. CHOROID

• Thin, highly pigmented, vascular loose connective tissue

• Rich in melanocytes gives characteristic dark color

• Situated between sclera & retina

• Extends from optic nerve to ciliary body (at ora serrata)

• Thickness decreases from post (0.22mm) to ant (0.1mm)

3. CHOROID• Functions:

• Nourishment for adjacent retina

• Block light entering through sclera, retain light entering through pupil

• 4 histological parts:

1. Suprachoroidal lamina

2. Choroidal stroma

3. Choriocapillaris

4. Bruch’s membrane

3. CHOROID

1. Suprachoroidal lamina

• Transition zone of choroid & sclera

• Consists of melanocytes, fibroblasts & conn. tissue fibers

• Blends with choroid & lamina fusca of sclera

• Carries long posterior ciliary arteries & nerves

3. CHOROID

2. Choroidal stroma

• Layer of pigmented, vascularised loose connective tissue

• Contains melanocytes, fibroblasts, macrophages, mast cells

• Arteries are branches of short posterior ciliaryarteries

• Veins drain via vortex veins into ophthalmic veins

3. CHOROID

3. Choriocapillaris layer

• Consists of rich capillary network

• Nourishes outer retina (eg PR) – damage will affect retina

• Capillaries are fenestrated

• Extends anteriorly to ora serrata

• Greatest density of capillaries at macula

3. CHOROID

4. Bruch’s membrane

• Extend from optic nerve head to ora serrata

• Thin refractile connective tissue membrane between choriocapillaris (choroid) and RPE (retina)

• Constitutes outer limit of retina

• Prevents choroid vessels from penetrating the retina but allows nutrients, proteins etc

RELATED DISORDERS

• Uveitis: inflammation of uveal tract eg. Iritis, choroiditis

• Age-related macular degeneration (AMD)

• Drusen (yellow deposits) in Bruch membrane at macula

• Horner’s syndrome: loss of symp innervation to the head

• Causes ptosis, anhydrosis, miosis

• Malignant choroidal melanoma

* tHE END *