Anatomy

The cornea is the sensitive transparent window at the front of the eyeball. It is approximately 0.5mm thick and is exposed directly to the air in front of it, and to a clear fluid (aqueous humour) behind it. It consists of collagen and cells on the front surface (epithelium) and back surface (endothelium). Corneal conditions include keratoconus, Fuch’s endothelial corneal dystrophy and pterygium.

The sclera is the tough white outer coat of the eye and is continuous with the cornea.

The conjunctiva is the thin clear mucous membrane covering the sclera and the inside surfaces of the eyelids.

The crystalline lens is located directly behind the iris and is able to change shape to alter the focus of the eye. Loss of clarity of the lens is known as a cataract.

The uvea is the middle layer of the eye situated between the retina and the sclera. It extends from the back of the eye towards the front and includes the:

• Iris - The coloured part of the eye that surrounds the pupil and controls the amount of light entering the eye.
• Ciliary Body - Controls the shape of the lens (accommodation) and produces aqueous humour.
• Choroid - The vascular layer under the retina.

The aqueous humour is a clear fluid produced by the ciliary body and located in the front part of the eye.

The vitreous humour is a clear gel that fills the back of the eye from the lens to the retina.

The trabecular meshwork is a meshwork of tiny canals (drainage pores) located at the junction (angle) where the cornea and the iris meet. Aqueous humour drains through this meshwork. The intraocular pressure is a balance between the amount of aqueous humour that is produced by the ciliary body and the amount that is drained through the trabecular meshwork. An increase in the intraocular pressure can lead to glaucoma.

The retina is a thin layer of light-sensitive tissue that lines the back of the eye. It functions like the film in a camera. The retina receives light messages and transmits them to the brain via the optic nerve for you to see.

The macula is the central part of the retina responsible for detailed central vision, as required for reading, driving, watching television, recognising faces etc.

The optic nerve is a bundle of approximately one million delicate nerve fibres which transmits the images from the retina to the brain for interpretation, allowing us to see. It can be affected by many diseases including glaucoma.

The anterior segment of the eye refers to the structures in front of the vitreous humour, including the cornea, iris, ciliary body and lens.

The anterior chamber of the eye refers to the space between the back (inner) surface of the cornea (the endothelium) and the front of the iris and lens.

The posterior segment of the eye refers to the structures in the back of the eye, including the vitreous humour, retina, choroid and optic nerve.