Posterior segment of eyeball

At a glance

English

Posterior segment of eyeball

Latin (TA2)

Segmentum posterius bulbi oculi

System

Eye

Region

Head

Side

Paired, left and right

About the posterior segment of eyeball

Eye specialists split the globe into an anterior and a posterior segment, with the dividing line at the front surface of the vitreous body, the anterior hyaloid membrane, just behind the lens. The posterior segment is everything behind that line and makes up roughly two-thirds of the eyeball. Its cavity, the vitreous chamber, is filled by the clear gel of the vitreous body, and its walls are formed by the three coats of the eye: the light-sensitive retina on the inside, the vascular choroid in the middle and the tough white sclera outside.

At the back of the segment the optic nerve leaves the eye at the optic disc, slightly to the nasal side of the posterior pole. The central retinal artery and vein enter and leave with it. About three millimetres to the temporal side of the disc lies the macula, with the fovea at its centre, where cone cells are packed most densely and detailed central vision is achieved. Forward, the sensory retina ends at the scalloped ora serrata, beyond which the segment meets the ciliary body.

The inner surface of the posterior segment that can be seen through the pupil with an ophthalmoscope is called the fundus. Inspecting it shows the disc, the macula and the retinal vessels, and it is the only place in the body where arteries, veins and an extension of the brain can be viewed directly without surgery. Changes here reflect diabetes, high blood pressure and raised pressure inside the skull.

Because its tissues are so specialised, disease of this segment is treated by retinal and vitreoretinal specialists. Typical problems are retinal detachment, age-related macular degeneration, diabetic retinopathy, blockage of retinal vessels, inflammation of the choroid and retina (posterior uveitis), and haemorrhage into the vitreous. Treatments include laser therapy, injections into the vitreous and vitrectomy, the surgical removal of the gel.

Function and supply

Function

Holds the vitreous body that keeps the globe's shape and lets light pass to the retina, where the image is converted into nerve signals for the optic nerve.