Vitreous Humor

Where is the vitreous humor located?

Adjacent to the lens and zonules, pars plana, the retina, and the optic disc. Takes up the posterior 80% of the globe.

What is the composition of the vitreous?

It’s similar to the AH but also contains a high content of collagen (II) and Hyaluronic Acid. Its functional cell is the hyalocyte which are similar in function and lifespan to keratocytes.

What is the function of the collagen and HA in the vitreous?

Provides consistency and transparency

Hyalocyte

Endogenous pluripotent cell of the vitreous humor. Responsible for secretion of the fibrinous component of the VH, phagocytosis of debris, act as macrophages for anti-inflammatory purposes, and have a contractile capability for fibrinous scar production.

Vitreous surfaces

Split into a posterior and an anterior region; made up of fine collagen fibers

Anterior hyaloid surface

More “formed” to keep out the AH but still very thin to promote transparency; anterior relative to the ora serrata

Posterior hyaloid surface

Less formed; limiting membrane helps to keep separation from the retina; posterior relative to the ora serrata

Where does the vitreous attach to the eye?

Vitreous base; Lens (Hyaloideocapsular ligament/Ligament of Weiger); Posterior pole (Peripapillary and Perimacular attachments)

Vitreous base attachment

Thickest collagen fibers here, which run perpendicular to the ILM and the hyaloid surface

Hyaloideocapsular Ligament/Ligament of Wieger

Posterior lens attaches to the anterior vitreous face and the posterior zonules (orbiculoposterior fibers) are involved in attachment

Patellar/Hyaloid Fossa

Space where the lens hangs out

Space of Berger

Potential space underneath the lens

Peripapillary Attachment

Ring of attachment at the optic disc, around the optic nerve.

Perimacular Attachment

Loose attachment at the macular region around large retinal blood vessels

How is the posterior hyaloid surface attached to the retina?

Attachment via collagen fibers that attach the ILM of the retina to the posterior face of the vitreous

Posterior Vitreal Detachment

Posterior vitreal face pops off and pulls away from the retina

Zones of the vitreous

Vitreal cortex (anterior and posterior), Intermediate zone, and central zone

Vitreal Cortex

Outermost zone surrounding the vitreous; made up of a thin layer of collagen fibers and HA; interior to the vitreal surface. High concentration of collagen and HA contributes to structural stability

Anterior cortex

Anterior to the vitreal base and adjacent to the ciliary body, posterior chamber, and the lens.

Posterior cortex

Extends posterior to the vitreal base

Intermediate zone

Core of the vitreous. Fibers are continuous and arise in the vitreal base. Decreased concentration of HA and collagen when compared to the cortex

Vitreal base

Part of the intermediate zone near the ora serrata. The cortex goes around it. It separates the anterior and posterior cortex as well as pars plana from the retina.

Central zone

Region at the center of the vitreous which runs from the posterior middle of the lens to the optic nerve. Contains Cloquet’s canal, the patellar fossa, and the prepapillary attachment.

Cloquet’s Canal

It is a leftover remnant of the Hyaloid artery that supplied nutrients to the eye during embryology.

1

Vitreous base (attachment)

2

Hyaloideocapsular ligament

3

Patellar fossa

4

Vitreal cortex

5

Berger’s space

6

Cloquet’s canal

7

Perimacular attachment/ bursa premacularis

8

Peripapillary attachment/area of Martegiani

9

Intermediate zone/ vitreal core

Vitreous functions

Exchange of metabolites, support the retina, optical transmission, eye growth, barrier

Exchange of metabolites

Exchange with the retina, lens, the choroid, aqueous humor, optic nerve, and the ciliary body

Optical transmission

Transparency d/t Hyaluronic acid and water composition; has a lower refractive index than the lens

Eye growth

VH provides signals for eye growth. Can be normal or abnormal

Barrier function

Keeps the aqueous and the vitreous where they’re suppposed to be

How does the vitreous change over time?

With age, the liquid:gel ratio changes (gets more watery); the vitreous shrinks and may pull away; fibres aggregate into sheets and collapse into bands; in general there is a freeing up of water

Vitreal syneresis

Vitreal shrinking that may result in the vitreous pulling away from its attachments

Persistent remnants of the vitreous humor

Floaters are likely debris, noticed d/t their motion and shadows.

Floaters

Muscae Volitantes