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Anatomy of vitreous

This document discusses the anatomy and development of the vitreous humor in the eye. It begins by describing the embryological origin of vitreous cells from surface ectoderm, neuroectoderm, and mesodermal tissues. During the primary vitreous stage, the vitreous body begins forming before closure of the choroidal fissure and appears as a fibrillated secretion filling the vitreous space. The document then covers the general features, structure including hyaloid layers, cortical and medullary regions, attachments, composition and transport processes of the mature vitreous humor. It concludes by describing the physicochemical properties and factors affecting expansion and contraction of the vitreous gel.

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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 parts 1. Hyaloid layer or membrane 2. Cortical vitreous 3. Medullary vitreous
Hyaloid layer • It is not a true membrane but outermost surface of vitreous 1. 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 components 1. Water 2. Collagen-like fibres 3. 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 vitreous FREEZES –expansion of vitreous
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