Fixatives for Tissue Preservation
Table 2-1 lists many of the fixatives and transport media used by pathology laboratories for various forms of analysis. The most commonly used fixative is 10% neutral-buffered formalin. Formalin is a 40% solution of formaldehyde that stabilizes proteins, lipids, and carbohydrates and prevents enzymatic destruction of the tissue (autolysis) by crosslinking proteins. In general, the volume of the fixative in which tissue is immersed should be at least 10 times the volume of the tissue. Formalin diffuses fairly quickly through tissue. Tissue fixation time varies depending on the size and composition of the specimen. When a globe is to be sent for pathologic evaluation, it is not necessary or desirable to open the eye, inject fixative, or create windows in the sclera, despite the relatively large size and volume of the globe. Furthermore, opening an eye before fixation may damage or distort sites of pathology, making histologic interpretation difficult or impossible. To ensure adequate fixation, an eye should be suspended in formalin (at least a 10:1 ratio of fixative to tissue) for at least 24–48 hours before processing. As different institutions may use different protocols, preoperative consultation with the pathologist is critical.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.