The pathologist's perspective on vitreous opacities

Vitreous opacities are diverse in nature. Many underlying diseases are sight-threatening and several are also lethal. This review presents the pathologist's perspective of vitreous opacities, correlates laboratory findings with the underlying disease and recommends safe methods for handling specimens. An aetiological classification of vitreous opacities is also proposed.

A gentle fixative such as Cytolyt or HOPE-fixation is required, unless delivery of the vitreous biopsy specimen to the laboratory can be guaranteed within two hours. Cells and other material are precipitated onto slides or into cell blocks by centrifugation. Light microscopy with the May-Grunewald Giemsa stain is enhanced, as necessary, by the use of special stains, such as Congo red for amyloid, Perl's for iron, Periodic Acid-Schiff for microorganisms, and several others. Immunocytological methods enable cell typing, using labels such as CD3 for T-cells in reactive inflammation; CD20 for B-cells in retinal lymphoma; CD34 and myeloperoxidase for myeloid leukaemic cells. The polymerase chain reaction enhances the identification of organisms in endophthalmitis and of immunoglobulin rearrangements in lymphoma.

Acquired vitreous opacities can be classified according to their aetiology as: genetic; inflammatory non-infectious; inflammatory infectious; inflammatory iatrogenic; degenerative, traumatic; neoplastic and idiopathic. Non-diagnostic vitreous biopsies, unfortunately, still do occur with the main causes of failure including small sample size; sampling error; inadequate fixation; and leakage from container during transport.

Vitreous biopsy can profoundly influence the outcome in patients with vitreous opacities. Success depends on close collaboration between clinicians, pathologists and microbiologists. Vitreous samples require proper handling and expert application of a wide range of specialized techniques.