Slide Preparation and Tissue Staining
Tissue sections in paraffin are usually cut at 4–6 μm. The cut section is colorless except for areas of indigenous pigmentation. Various tissue dyes—principally hematoxylin and eosin (H&E) and periodic acid–Schiff (PAS)—are used to stain the tissue section in order to visualize the tissue under the microscope. The stains provide contrast and color, making it possible for pathologists to identify cellular elements (nuclear versus cytoplasmic). They also highlight various cellular and extracellular structures, depending on their chemical composition (Table 2-2). A small amount of resin is placed over the stained section and covered with a thin glass coverslip to protect and preserve it.
Special histochemical stains
Pathologists employ special histochemical stains to identify organisms and constituent substances present in tissue, supplementing the information available through examination of tissue using routine stains such as H&E. Special stains are typically performed on the basis of changes identified by the pathologist on routine stains or when a particular diagnosis is suspected clinically. These stains are performed on permanent sections, with the exception of oil red O, which requires a frozen tissue section instead of paraffin-processed tissue. See Table 2-2, which lists the histochemical stains commonly used in ophthalmic pathology.
Table 2-2 Histochemical Stains Commonly Used in Ophthalmic Pathology
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.