ANATOMY OF VITREOUS

DR RAKESH JAISWAL

Embryology of vitreous

Cells of origin of the vitreous gel include•Cell of the surface ectoderm(lens anlage)•Cell of the neuroectoderm(retina and ciliary epithelium )•Mesodermal cells b/w the surface and neural ectoderm at the anterior rim of the developing optic cup•Mesodermal cells migrating into optic cup via fetal fissure with hyaloid system

PRIMARY VITREOUS STAGE

•primary vitreous body begins its formation before the closure of the chorioidal fissure• Primary vitreous appears at the time of formation of the optic cup, is a fibrillated secretion of the retinal cells, and fills in the vitreous space with a feltwork of fine fibrils•Primary cellular vitreous formation•Vascularization of primary vitreous •Its mixed ectodermal and mesenchymal origin

Congenital and development abnormalities

•Mittendorf dot•Muscae volitantes•Persistent hyloid system•Vitreous cyst

Failure of secondary vitreous •COLOBOMA•Vitreous tracts ,Transvitrous channel

GENERAL FEATURES• Vitreous humour is an inert,transparent,coloursless,jelly-

like structure• Hydrophilic gel serves as optical functions and act as

important supporting structure for eyeball • Anteriorly-by post surface lens and ciliary body• Posteriorly-by retina

• wt-4g• Vol-4cc (2/3vol of entire globe)

approximately 99 % water 1 % solid

• 0.9% salts• 0.08% protein• 0.02% mucopolysaccharide

STRUCTURE

• The vitreous is the largest and simplest connective tissuse present as a single piece in the human body

• Divided in 3 parts1. Hyaloid layer or membrane2. Cortical vitreous3. Medullary vitreous

Hyaloid layer • It is not a true membrane but outermost

surface of vitreous1. Ant hyaloid membrane (ant limiting

membrane layer)2. Post hyaloid membrane (post limiting

membrane layer)

Ant hyaloid membrane

• It covers vitreous body ant 1.5mm from the ora serrata• Lies in contact with pars plana,ciliary processes,ciliary zonules and

post lens capsule(form ring about 9mm in diameter called as hyaloido-capsular ligament of wieger in center of it space called Berger’s space

• It connect with other intraocular structures by following fine ligaments

Hyalociliary zonules-AHM to valley b/w ciliary processes

• Retrolental ligament-AHM to lens• Coronary ligament- its fibres extend AHM to

inner face of the post third of ciliary processes circumferentially

• Median ligament-it also runs circumferentially from AHM at the level of mid zone of pars plana

Posterior hyaloid membrane

• It extends back from the vitreous base up to the optic disc

• It lie in contact with the internal limiting membrane of the retina

Cortical vitreous• It lie in peripheral zone appox 100 micron in width • It is more condensed fibrillar vitreous• It contain Type 2 collagen fibrils interspersed with

the sodium hyaluronate ,mucopolysaccharide molecules which provide viscosity ,elasticity and tensile strenght to it

• 2 percent of the total vitreous vol• It is the metabolic centre of the vitreous

body(vitreous cells –hyalocytes)• Vitreos cells synthesize the hyaluronic acid

Medullary vitreous

• Majority of vitreous body is form by central medullary vitreous

• Similar to cortical vitreous except it is less fibrillar structure and cell free

Vitreous tracts• Vitreous tracts are fine sheet like condensations of vitreous tissue which radiate into the

virteous space from ciliary body and ant retina•

Topographic subdivisions of vitreous space

ATTACHMENTS OF THE VITREOUS

• OPTIC DISC• BACK OF LENS• FOVEAL REGION • ORA SERRATA

BIOCHEMICAL COMPOSITION

• Composed of 3 major structural components1. Water2. Collagen-like fibres3. Hyaluronic acid a glycosaminoglycans(GAGs)

TRANSPORT PROCESSES

• The active pump mechanisms located at level of ciliary body ,pigment epithelium and possible retinal vessels are concerned with active transport of materials across the vitreous

PHYSICOCHEMICAL PROPERTIES• Wt -4g• Vol-4cc• Refractive index-1.3349 it transmit almost 90%

of light b/w 300-1400 nm• Plasticity-provided by 3D collagen fibres which

is electrostatically neutral bec they are not cross linked and allow vitreous vol to expand

• Viscoelasticity-provided by network of hyaluronic acid molecular chain

VITREOUS EXPANSION AND CONTRACTION

Its is a funtion of ionic charge of the vitreous structure

POSITIVE CHARGE NEGATIVE CHARGE Na Hyaluronic acid Nacl Protien mol TEMP AND PH –cause shrinkage of vitreousFREEZES –expansion of vitreous

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