Globes & Contents

The cornea and sclera constitute the outer layer of the eye.

Cornea

Transparent avascular tissue covering the iris, pupil and anterior chamber. Its primary function is to refract light, accounting for two-thirds of the eye’s total optical power.

Layers

1. Corneal epithelium – thin layer of epithelial
2. Bowman’s layer – tough layer of collagen
3. Corneal stroma – thick, transparent middle layer
4. Descemet’s membrane – thin acellular layer serving as a modified basement membrane of the corneal endothelium
5. Corneal endothelium – simple think layer of mitochondria rich cells

Innervation

• Densely innervated with sensory nerve fibres via the ophthalmic branch of the trigeminal nerve

Sclera

The opaque white, fibrous outer layer of the eye. It forms more than 80% of the surface area of the eyeball extending from the cornea all the way to the optic nerve and is continuous with the dura mater posteriorly. Anteriorly it is continuous with the limbus of the cornea. It provides protection to the eye and an attachment for the insertion of extraocular muscles.

Choroid

The choroid is a highly vascular layer of the eye and lies between the retina and sclera. It is important to the nutrient and oxygen exchange with the outer retina.

Blood supply

• Uveal circulation
  • Derived from branches of the ophthalmic artery
  • Supplies the uvea, middle and outermost layers of the retina
• Retinal circulation
  • Derived from the central retinal artery
  • Supplies

Posterior ciliary arteries (from the ophthalmic artery)

mater posteriorly. Anteriorly it is continuous with the limbus of the cornea. It provides protection to the eye and an attachment for the insertion of extraocular muscles.

Iris

Pigmented muscular curtain that lies between the cornea and lens, forming a circular aperture termed the pupil. 

Layers

1. Stroma – front pigmented fibrovascular layer, connected to the sphincter pupillae which contracts the pupil and dilator pupillae which enlarges the pupils
2. Pigmented epithelial cells