The eye wall: cornea, sclera, uvea and lens !

Organ

The eyeball has three layers: a tough outer coat that is clear at the front, a middle layer full of vessels and pigment, and the retina inside.

Updated 2026-11-01

See it in 3D: Cornea · Sclera · Iris · Lens

What it is

The wall of the eyeball is built from three tunics: the fibrous tunic (cornea and sclera), the vascular tunic or uvea (choroid, ciliary body and iris) and the neural tunic (retina). The cornea and lens are clear because they have no blood vessels and their parts are laid out with great regularity; any disorder in that layout shows up as clouding. Knowing each layer explains common diseases such as cataract and glaucoma.

Structure

Fibrous tunic: the cornea in front (clear, avascular, densely innervated) and the sclera behind (dense type I collagen connective tissue, white and opaque).
Limbus (corneoscleral junction): where the corneal epithelial stem cells live and, at the iridocorneal angle, the trabecular meshwork and Schlemm's canal.
Choroid: loose stroma rich in vessels and melanocytes; its innermost layer, Bruch's membrane, supports the retinal pigment epithelium.
Ciliary body: ciliary muscle (smooth) and ciliary processes covered by a two-layer epithelium that secretes aqueous humor.
Iris: stroma with melanocytes, the sphincter pupillae (smooth muscle, parasympathetic), the dilator pupillae (myoepithelial, sympathetic) and a heavily pigmented posterior epithelium.
Lens: a thick capsule (basal lamina), a simple cuboidal epithelium on the anterior surface only, and lens fibres with no nucleus or organelles, packed with crystallins; held by the zonular fibres.

Layers of the cornea (front to back)

Layer	What you see	Key fact
Corneal epithelium	Non-keratinized stratified squamous epithelium, a few cells thick	Renews quickly from the limbus; richly innervated, which is why an abrasion hurts so much
Bowman's layer	Acellular band of collagen fibrils under the epithelium	Does not regenerate: injury leaves a scar
Stroma	Parallel, orderly lamellae of type I collagen with keratocytes	Most of the thickness; the regular spacing of the fibres makes it transparent
Descemet's membrane	Thick basal lamina of the endothelium	Copper deposits here form the Kayser-Fleischer ring of Wilson disease
Endothelium	Single layer of simple squamous cells	Pumps water out of the stroma to keep it clear; barely divides in adults

Clinical notes

Cataract: clouding of the lens fibres, mostly with age; diabetes and corticosteroids make it more likely.
Open-angle glaucoma: outflow through the trabecular meshwork is impaired, intraocular pressure rises and the optic nerve is damaged.
When the corneal endothelium fails, the stroma swells with water and the cornea loses its clarity.

Test yourself

Think of the answer, then tap the question to see it.

Which corneal layer does not regenerate and scars when injured?

Bowman's layer, an acellular band just under the corneal epithelium.

Which epithelium produces aqueous humor?

The two-layer epithelium covering the ciliary processes of the ciliary body.

Why is the cornea transparent?

It has no blood vessels, its collagen lamellae are highly ordered and the endothelium keeps the stroma dehydrated.

In which corneal layer does copper deposit in Wilson disease?

In Descemet's membrane, where it forms the Kayser-Fleischer ring.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

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Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.

Sources: 14.1 Sensory Perception (OpenStax, Anatomy and Physiology 2e, 2022); How the Eyes Work (National Eye Institute (NIH), 2026); Cataracts (National Eye Institute (NIH), 2026).

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Representative model, for educational purposes only.