Pathology of the Vitreous

The vitreous body is a clear gel matrix that fills the posterior segment cavity of the eye that, unlike the aqueous, is relatively stagnant. This avascular structure is composed mostly of water, inorganic salts, protein (collagen), polysaccharides, ascorbic acid, and rare cells (phagocytes, hyalocytes/macrophages). Interestingly, the vitreous has an inept immunology due to the absence of immunoglobulins and adaptive immune cells. Multiple infectious, inflammatory, and neoplastic conditions may affect the vitreous that may pose as significant diagnostic challenge given their potentially similar clinical presentations. Vitreous sampling using pars plana vitrectomy serves as a tool to ascertain the diagnosis of patients with cells in the vitreous when history, ophthalmic exam, and laboratory tests are inconclusive. General indications for diagnostic vitrectomy include uveitis with an atypical clinical course and refractory to treatment, suspected inflammatory or infectious endophthalmitis (viral, bacterial, fungal, or parasitic), suspected retained intraocular foreign body, degenerative disorders, congenital abnormalities, or suspected intraocular malignancy. Diagnostic pars plana vitrectomy can be performed alone or as part of a therapeutic procedure. Specimen handling and processing will vary between cases depending on the differential diagnosis.