Vitreous
Home / Ophthalmic Pathology / Vitreous
Introduction
There are 3 fluid filled compartments in the eye:
- Anterior chamber
- Posterior chamber
- Vitreous cavity
The vitreous cavity is the largest of these compartments. The volume of the vitreous cavity makes up approximately four-fifths of the total volume of the globe, and contains an average volume of approximately 4mL of gel-like fluid. The vitreous is transparent, and functions in transporting nutrients to the lens, ciliary body and retina. The vitreous is about twice the viscosity of water, due to mucopolysaccharide hyaluronic acid. Hyalocytes are found in the vitreous, which are believed to be modified histiocytes, glial cells or fibroblasts. Fine collagen fibrils are also found which are composed mostly of type II collagen. The larger fibers are interspersed in the vitreous and connected by the fine connecting fibrils, with liquid channels and hyaluronic acid filling the space between these fibers and fibrils.
The vitreous fibrils merge with the non-pigmented epithelium of the pars plana and the internal limiting membrane (ILM) of the retina. The vitreous also adheres to the disc margin, near the macula, and along retinal vessels. Anteriorly, the vitreous adheres to the posterior lens capsule via the hyaloideocapsular ligament. During fetal development a hyaloid vasculature emerges that connects the posterior pole of the lens to the margin of the optic nerve head. Regression of this fetal vasculature may leave a Cloquet canal, and in adults a “Mittendorf dot” may appear on the lens as a normal variant.
Vitreous consists of 99% water, and is composed of Type II + IX collagen, glycoproteins, and other soluble proteins.The most secure attachment of vitreous is to vitreous base,which is a 360° band that straddles ova serrata and this extends more posteriorly w/ increasing age.
There are 5 Vitreous attachments:
- Vitreous base (strongest)
- Margins of optic nerve head
- Along major retinalvessels
- Circular area around fovea
- At edges of lattice degeneration
Vitreous Embryology
Embryologic development proceeds in 3 stages:
- Primary vitreous –fibrillary components, mesenchymal cells, vascular components: the hyaloid artery, vasa hyaloide a propria, and tunica vasculosa lentis
- 2° vitreous –9th weeks gestation–primary vitreous degenerates to become hyaloid canal secondary vitreous develops as a relatively acellular and avascular structure. The cells of secondary vitreous are called hyalocytes.
- 3° vitreous –lens zonular fibers-aka “zonules of Zinn”
Vitreous Pathology
Development
Persistent Fetal Vasculatureor PFV(formerly known as persistent hyperplastic primary vitreousor PHPV)
Slit Lamp Photograph of Bergmeister Papillae
Gross Photograph of Bergmeister Papillae
Gross Photograph of remnant hyaloid artery
Low magnification view of remnant hyaloid artery
External slit lamp photograph of clinically significant PHV
Mass in the lens pulling and contracting the ciliary processes forward
Gross Photograph of mass with remnant hyaloid artery
Gross photograph of mass with optic nerve stalk
Low magnification view of mass pushing ciliary body
- Typically recognized in 1st few weeks of life
- Unilateral in 2/3
- Ultrasound shows no tumor, short axial length +/-calcification
Bergmeister Papillae
- Posterior remnant of hyaloid artery
- Veil-like structure over optic nervehead or
- Small finger-like projection from optic nerve, may be vascular and loop back toward optic nerve head, creating a loop
Mittendorf Dot
- Anterior remnant of hyaloid artery
- Focal lens opacity
- Just inferior and nasal to lens center
Vitreous Cyst
- Usually isolated finding, with no associated pathology
- Histological studies show hyaloid remnants with cysts
Clinically significant PFV
- Fibrovascular plaque in the retrolental space
- May extend to involve ciliary processes
- Eye may be microphthalmic, cataractous, have shallow anterior chamber/hypoplastic iris
- Often traction and non-ocular tissues such as adipose or hyaline can be found at the retrolental mass
- May have closed funnel retinal detachment
- Treatment is vitrectomy/lensectomy
Inflammatory conditions
- Since the vitreousis avascular, it is not typically an active inflammation source.
- Inflammation of the vitreous by white blood cells is known as vitritis
- Marked neutrophilic infiltration (vitreous cell)may lead to liquefaction of vitreous
- Secondary inflammatory involvement of the vitreous due to infection is known as endophthalmitis
- Usually bacterial or fungal
Degeneration
Syneresis: Liquefaction of the gel
- Almost universal process that occurs with aging
- Also occurs with vitreous inflammation, hemorrhage, pathologic myopia
- An abnormal aggregation of vitreous fibers around areas of syneresis can lead to a lamellae and stranding appearance
- Vitreous syneresis contributes to vitreous detachment
Vitreous Hemorrhage:
- After 2-10 days, blood clots undergo fibrinolysis
- Red blood cell breakdown leads to ghost cells, aggregation of these cells in trabecular meshwork may cause ghost cell glaucoma
- Cholesterol crystals may also form due to breakdown of red blood cell membranes, which may attract macrophages which may coalesce to form giant cells
Slit lamp photograph of Asteroid Hyalosis
Gross Photograph of Asteroid Hyalosis
Photomicrograph of asteroid bodies
Polarized light photomicrograph of asteroid body, showing birefringence
Slit lamp photograph of Synchysis scintillans
Asteroid Hyalosis:
- A striking clinical finding with less striking clinical significance.
- Asteroid bodies form in the vitreous, which are round 10-100nm particles that attach to vitreous fibrils
- Stain with alcian blue and other stains for neutral fats, phospholipids and calcium
- May be associated with rare giant cells, butare non-inflammatory
- The structures themselves are structurally similar to hydroxyapatite and show birefringence under polarized light
- May be confused with Synchysis scintillans: crystals of cholesterol that acculumate as vitreous liquefies; appear as small white to yellow floaters (like a snow globe)
Vitreous Amyloidosis:
- Amyloidosis refers to systemic deposition of amyloid, which is a tertiary protein structure of a ß-pleated sheet.
- These proteins bind congo red and have birefringence under polarized light
- Deposits of transthyretin (pre-alloumin) is the source of amyloidosis in the vitreous
- Familial amyloid polyneuropathy (FAP) is a genetic condition associated with altered transthyretin protein.
- Associated with vitreous opacities, perivascular infiltrates,peripheral neuropathy, cardiomyopathy, carpal tunnel
- Unclear how amyloid gets into vitreouscavity
- May be from vascular source, via blood aqueous or blood-retina barrier
Gross Photograph of PVD
Posterior Vitreous Detachment(PVD):
- Dehiscence in vitreous cortexallows fluid from syneretic cavity into potential subhyaloid space
- Fluid causes anterior detachment over hours to days
- 31-65% of patients will have PVD by age 65
- PVD plays role in pathogenesis at macular hole, RD, vitreous hemorrhage
Gross Photograph of funnel-shaped RDR
Rhegmetogenous RD: retinal tear from trauma or PVD
- Tears are most common at highest adhesion sites
- Histology shows vitreous adherent to tear at its edge
- The principle findings of this condition are:
- Degeneration of photoreceptorouter segments
- Apoptosis of photoreceptors
- Migration of Müller cells
- Proliferation and migration of RPE cells
- A membrane may form on either face of retina. This is known as proliferative vitreoretinopathy (PVR)
- Hyalocytes, fibroblasts, glial cellsand other cells proliferate to cause membrane growth
Neoplasms
- Few primary vitreous tumors due to relative acellularity, with the exception of lymphoma
Vitreous Lymphoma:
- B-cell lymphomais most common, T-cell lymphomas are rare
- May present with sub RPE infiltrates (minority of cases), visible as speckled pigment over the tumor of detachments of the RPE
- 50% will have concomitant CNS involvement
- Diagnosis is challenging, must have cytologyanalysis of vitreous
- As with other ocular lymphomas, staining for clonality will show monoclonal population of cells
- Smear will show atypical lymphocytes, necrotic smudgy cells
- Other useful tests include IL-10 to IL-6 ratio
- Subretinal/sub-RPE infiltrates may resolve and atrophy with or without treatment. Choroid is typically not involved and free of lymphoma cells, but may be damaged secondary to longstanding inflammation.
- Contrast with systemic lymphoma with secondary ocular involvement, where the choroid is the main site