Anterior segment of eyeball

At a glance

English

Anterior segment of eyeball

Latin (TA2)

Segmentum anterius bulbi oculi

System

Eye

Region

Head

Side

Paired, left and right

About the anterior segment of eyeball

Clinicians divide the eyeball into two segments, the boundary being the vitreous body's anterior surface. Everything ahead of that boundary belongs to the anterior segment, which takes up roughly the front third of the globe. Its structures are the transparent cornea at the very front, the coloured iris with its central pupil, the ciliary body forming a ring behind the iris root, and the lens hanging from the ciliary body on its zonular fibres. The conjunctiva and the corneoscleral limbus are often counted with it in clinical practice.

Two small fluid spaces lie inside it. The anterior chamber sits between the endothelium on the back of the cornea and the front of the iris. The posterior chamber is a thin ring behind the iris, bounded behind by the lens, the zonule and the front of the vitreous. Both hold aqueous humour, which the ciliary processes make in the posterior chamber. It passes through the pupil into the anterior chamber and drains at the iridocorneal angle into the scleral venous sinus.

Much of the optical work of the eye is done here. The curved front of the cornea provides most of the eye's focusing power, the iris controls how much light enters, and the lens, adjusted by the ciliary muscle, fine-tunes focus for near and far objects. The aqueous humour supplies oxygen and nutrients to the cornea and lens, which lack blood vessels, and keeps the pressure that holds the shape of the front of the globe.

Disorders of this segment form a distinct branch of eye care and can largely be examined with a slit lamp. They include corneal injury and infection, cataract of the lens, inflammation of the iris and ciliary body (anterior uveitis) and glaucoma arising from impaired drainage at the angle.

Function and supply

Function

Admits and focuses light, controls the amount reaching the retina, adjusts focus for distance, and produces and drains the aqueous humour.