<ul>
 <li>Largest cavity in the eye&nbsp;</li>
 <ul>
 <li>2/3rds of total volume (approx 3.9ml in emmetropic eyes)</li>
 <li>3.9g weight</li>
 </ul>
 <li>Transparent viscoelastic gel</li>
 <li>98% water and 0.15% macromolecules</li>
 <li>Structure: collagen network interspersed with hyaluronic acid</li>
 <ul>
 <li>Hyaluronan provides viscosity, viscoelasticity and stability.&nbsp;</li>
 <ul>
 <li>Polysaccharide GAG: nontoxic, noninflammatory and nonimmunogenic</li>
 </ul>
 </ul>
</ul>

<HotTopic>
 There is no regeneration of collagen in the vitreous or rebuilding of the structure after
 syneresis
</HotTopic>
<ul>
 <li>Also contains:&nbsp;</li>
 <ul>
 <li>
 Albumin, transferrin, tPA (for fibrinolysis after VH?) fibronectin, fibulin, opticin, VIT1,
 hyaluronidase, fibrillin (component of zonules) and MMP-2
 </li>
 <li>
 Opticin and VIT1 are novel glycoproteins that maintain the structure of the collagen fibrils
 </li>
 </ul>
 <li>
 Higher glycoprotein content than aqueous: glycoproteins are produced by the ciliary epithelium
 </li>
</ul>
<HotTopic>
 Na/K concentrations are the same as in the aqueous
</HotTopic>
<ul>
 <li>High ascorbic acid concentration due to active transport by the ciliary epithelium</li>
 <li>Acellular, although occasional cells may be found in the cortex</li>
 <ul>
 <li>
 Single layer of hyalocytes line the vitreous cortex
 </li>
 <li>Produce hyaluronan</li>
 <li>There are fibroblast-type and macrophage-type hyalocytes</li>
 </ul>
 <li>Saturated and unsaturated fats are present</li>
 <li>RI of 1.33 (similar to aqueous)</li>
 <li>Does not transmit light of wavelengths below 300nm</li>
 <li>Anterior depression called the hyaloid fossa holds the lens</li>
</ul>
<ul>
 <li>
 The outer &ldquo;cortical&rdquo; zone comprises densely arranged collagen fibres compared to the
 central vitreous which is more liquid and has less collagen
 </li>
 <li>
 There is a &ldquo;previtreal&rdquo; space anteriorly between the pre-lenticular part and the
 vitreous base at the ora
 </li>
</ul>

<HotTopic>
 The central vitreous contains a fluid filled canal (hyaloid or Cloquet&rsquo;s canal) which is
 the remnant of the hyaloid artery
</HotTopic>
<ul>
 <li>Viscosity decreases with age</li>
</ul>
Vitreous functions:
<ul>
 <li>Maintain transparency</li>
 <li>Conduit for nutrient/solutes to the lens</li>
 <li>Inhibitor of angiogenesis (this quality is reduced in diabetic vitreoretinopathy)</li>
 <li>Non-compressible shock absorber</li>
 <li>Retards the bulk flow of fluid</li>
</ul>

## Embryology
<ul>
 <li>5 weeks: Primary vitreous comprising hyaloid artery and its branches</li>
 <li>5-12 weeks: Secondary vitreous (avascular) deposited behind the primary vitreous&nbsp;</li>
 <ul>
 <li>Secreted by the retina</li>
 <li>Attachments to ILM</li>
 <li>Early hyalocytes of the mononuclear phagocytes system</li>
 <li>Deposit fibrillar material</li>
 <li>Generate the microglia of the retina</li>
 </ul>
 <li>3 months: Tertiary vitreous</li>
 <ul>
 <li>Secreted by neural ectoderm of ciliary body</li>
 <li>Condenses around the optic cup margin and lens</li>
 <li>Matures to form the vitreous base</li>
 <li>Includes the zonules</li>
 </ul>
 <li>
 Tunica vasculosa lentis (hyaloid vessel and branches) regresses and atrophies while the retinal
 vessels form
 </li>
 <ul>
 <li>30 weeks: blood flow in the hyaloid artery stops</li>
 <li>34-35 weeks: loses connection to the optic nerve and disappears</li>
 <li>Remnant becomes Cloquet&rsquo;s canal</li>
 </ul>
</ul>
<ClinicalCorrelate>
 Persistent hyperplastic primary vitreous can cause leucocoria
 (other causes being retinoblastoma, Coat&rsquo;s disease and toxocara etc.)

</ClinicalCorrelate>
<ul>
 <li>Much of the hyaluronan and type II collagen is deposited after birth</li>
</ul>

## Vitreous collagen
<ul>
 <li>90% is Type II collagen and forms major component of the fibrils</li>
 <li>
 10% is Type IX collagen and there are cross-links between some type II and type IX molecules
 </li>
 <ul>
 <li>Forms the surface of the fibrils</li>
 </ul>
 <li>Types V/XI (thought to be unique to the vitreous) are found in small amounts</li>
</ul>
<HotTopic className='mb-6'>
 The posterior hyaloid membrane seen following PVD stains for type IV collagen&nbsp;
</HotTopic>
<ClinicalCorrelate>
 
 Stickler&rsquo;s syndrome is an autosomal disorder of type II
 collagen causing vitreous abnormalities with premature vitreous collapse and a high risk of GRT
 and RD.
 
</ClinicalCorrelate>

## Vitreous attachments
<ul>
 <li>Cortical vitreous attached by condensations of fine collagen fibres</li>
</ul>

<HotTopic>
 
 Areas of attachment:
 

<div>
 <ul>
 <li>Peripheral retina and pars plana (3-4mm wide band of vitreous base)</li>
 <li>Posterior lens capsule (ligamentum hyaloide capsulare or Wieger&rsquo;s ligament)</li>
 <ul>
 <li>
 The canal of Petit lies between the anterior vitreous cortex and the postero-capsular bundle
 </li>
 </ul>
 <li>Retina at the optic disc margins (base of the hyaloid canal)</li>
 <li>Inner limiting membrane especially along the retinal vessels (variable)</li>
 <li>Edges of lattice degeneration</li>
 </ul>
</div>
</HotTopic>


## Liquefaction
<ul>
 <li>The vitreous gel undergoes liquefaction with age</li>
 <ul>
 <li>Age-related loss of type IX collagen leading to fibril breakdown</li>
 <li>Hyaluronan is degraded</li>
 <li>Collagen fragments clump into fibrillar opacities</li>
 <li>ILM adhesions loosen</li>
 </ul>
 <li>Myopia is associated with earlier liquefaction</li>
 <ul>
 <li>Associated with changes in the concentrations of collagen and hyaluronan</li>
 </ul>
 <li>May lead to posterior vitreous detachment</li>
 <ul>
 <li>Occurs in 50% of the population</li>
 <li>
 Often sudden: central liquefied vitreous passes through a hole in the cortical vitreous and
 strips the remaining cortex off the ILM
 </li>
 <li>Retinal tear can occur</li>
 <li>
 PVD may protect against proliferative diabetic retinopathy by removing a scaffold for
 fibrovascular proliferation
 </li>
 </ul>
</ul>

## Anterior persistent fetal vasculature**
<ul>
 <li>A differential in leucocoria</li>
 <li>Most common cause of unilateral congenital cataract</li>
 <li>Persistent hyaloid artery results in a white retrolental mass</li>
 <li>Associated with</li>
 <ul>
 <li>Microphthalmos (cp with Rb which is very rare in microphthalmic eyes)</li>
 <li>Shallow AC</li>
 <li>
 Long ciliary processes
 </li>
 <li>Guarded visual prognosis due to glaucoma, cataract, deprivational amblyopia</li>
 <li>Tractional retinal detachment in severe cases</li>
 <li>M=F</li>
 <li>Present at birth</li>
 </ul>
 <li>
 Management: difficult. Early cataract removal, membrane excision, CL wear, amblyopia treatment
 </li>
</ul>

Posterior segment

Vitreous

Intro

FRCOphth Part 1 Study Notes

Orbit and ocular adnexae

Orbit

Extraocular Muscles

Orbital Blood Vessels

Paranasal Sinuses

Lacrimal Glands

Tear Film

Eyelids

Blinking

Anterior segment - ocular surface

Conjunctiva

Conjunctivitis

Sclera

Cornea

Corneal Structure And Development

Corneal Physiology

AC to Lens

Angle

Ciliary Body

Aqueous Humour Dynamics

Iris

Pupil

Lens

Choroid

Retinal Macrostructure

Neurosensory Retina

Retinal Pigment Epithelium

Neuroanatomy

Venous Sinuses

Cerebral Ventricles

Cerebral Blood Supply

Supranuclear Gaze Pathways

Head And Neck Autonomic Nervous Supply

Head And Neck Glands

Osteology

Nerves

Muscles And Pharyngeal Arches

Extraocular Nerves

Sensory Nerves

Physiology

Physics Of Blood Flow

Neuronal Control Of Blood Vessels

Oxygen-Haemoglobin Dissociation Curve

Cytochrome p450

Pituitary Gland

Thyroid Hormone Production

Insulin

Glucagon

Parathyroid Hormone

Corticosteroids

Catecholamines

Cardiac Cycle

Renal Physiology

Fluid Balance

Acid-Base Balance

Muscle Physiology

Sensory Fibres

Cutaneous Receptors

Endocytosis

Glycosaminoglycans

Condensed Ocular Biochemistry

Eye Movements

Accomodation

Vision

Visual Cycle And Phototransuction

Visual Pathway

Visual Acuity

Colour Vision

Binocular Vision

Pathology

Collagen

Tissue Damage

Inflammation

Disease Entities

Wound Healing

Thrombosis / Atherosclerosis

Cell Growth

Neoplasia

Histopathology

Nystagmus

Free Radicals And Antioxidants

Immunology

Ocular Immunology

Microbiology

Viral Infections

Bacterial Infections

Fungal Infections

Protozoa

Nematodes

Antimicrobials

Genetics

Chromosomes

Mitosis

Meiosis

Genes

Polypeptide Synthesis

Histones

MicroRNA

Hardy-Weinberg Equilibrium

Mutations

Chromosome Defects

Autosomal Inheritance

X-Linked Inheritance

Mitochondrial Inheritance

Multifactorial Inheritance