Overview

Volume≈4 mL (≈80% of globe)

Water content≈99%

The vitreous is ≈99% water, given gel properties by a sparse network of thin type II collagen fibrils stabilised and spaced by hyaluronan. It contains very few cells (hyalocytes, macrophage-like cells in the cortex). Its outer condensed layer (cortex) is firmly attached at the vitreous base (straddling the ora serrata), and less firmly around the optic disc, along major retinal vessels and at the macula. Anteriorly it forms the hyaloid fossa (patellar fossa) for the lens.

The hyaloid canal (Cloquet canal) runs from the optic disc to the back of the lens — the remnant of the path of the embryonic hyaloid artery. Unlike aqueous humour the vitreous is not continuously replaced; once lost (e.g. at surgery) it is replaced by aqueous-like fluid.

With age the gel progressively liquefies (syneresis) and collapses, and eventually separates from the retina — posterior vitreous detachment (PVD), occurring in most people over 60. Traction at sites of firm adhesion during PVD can tear the retina.

Location: Vitreous chamber: behind the lens and zonule, enclosed by the ciliary body and retina.

Anatomy

Histology: Hydrogel: type II collagen (with IX, V/XI), hyaluronan, hyalocytes; no blood vessels.
Development: The primary vitreous (vascular, containing the hyaloid artery) is replaced by the avascular secondary vitreous; the tertiary vitreous forms the zonule. Failure of regression gives persistent fetal vasculature (persistent hyperplastic primary vitreous), a cause of leukocoria.

Function

Transmit light to the retina (refractive index ≈1.336)
Maintain the shape of the globe and hold the retina against the RPE
Act as a shock absorber and metabolic reservoir/diffusion barrier

Clinical significance

Floaters and posterior vitreous detachment

Floaters are shadows cast on the retina by vitreous condensations. A sudden shower of floaters with flashes (photopsia from retinal traction) suggests PVD, which in ≈10–15% of symptomatic cases is accompanied by a retinal tear — needs urgent dilated fundus examination.

Vitreous haemorrhage

Bleeding into the vitreous (proliferative diabetic retinopathy, retinal tear, trauma) causes sudden painless loss of vision or a "shower of dark spots", with loss of the red reflex.

Intravitreal injections and vitrectomy

Anti-VEGF agents and steroids are injected through the pars plana into the vitreous. Vitrectomy removes the gel to repair retinal detachment, clear haemorrhage or treat macular holes.

Compiled from standard anatomy and physiology references — see the Special Senses sources. For education only; not medical advice.