General Aspects of Wound Repair
The purpose of wound healing is to restore the anatomical and functional integrity of an organ or tissue as quickly as possible. Although it is a common physiologic process, wound healing involves a complicated sequence of tissue events. The process may take many months, and the end result is typically a scar (Fig 4-1). When wound healing occurs in the eye, it can interfere with vision. There are 3 general phases of wound healing:
Inflammatory phase: The acute inflammatory phase may last from minutes to hours. Blood clots quickly in adjacent vessels in response to tissue activators. Neutrophils and fluid enter the extravascular space. Histiocytes (also called macrophages) remove debris from the damaged tissues, and new vessels form. Fibroblasts begin to produce collagen, the main structural protein in connective tissues. Collagen plays multiple roles in wound healing, including interacting with platelets to initiate the inflammatory phase and functioning as a scaffold or guide for fibroblast migration.
Proliferative phase: Regeneration is the replacement of lost cells and occurs only in tissues composed of cells capable of undergoing mitosis throughout life (eg, epithelial cells, fibroblasts).
Remodeling phase: Repair is the process of restructuring of tissues to recapitulate normal tissue and typically results in a fibrous scar. In this final phase, contraction causes the reparative tissues to shrink so that the scar is smaller than the surrounding uninjured tissues. This process may affect adjacent tissues and structures. Both repair and contraction of wounds are highly dependent on fibroblasts.
Figure 4-1 Sequence of general wound healing with an epithelial surface. 1, The wound is created. Blood clots in the vessels; neutrophils migrate to the wound; the wounded edges begin to disintegrate. 2, The wound edges are reapposed with the various tissue planes in good alignment. The epithelium is lost over the wound but starts to migrate. The stromal/dermal fibroblasts enlarge and become activated. Fibronectin is deposited at the wound edges. The blood vessels begin to produce buds. 3, The epithelium seals the surface. Fibroblasts and blood vessels enter the wound and lay down new collagen. Much of the debris is removed by histiocytes. 4, As the scar matures, the fibroblasts subside. Newly formed blood vessels canalize. New collagen strengthens the wound, which contracts. Note that the striated muscle cells in the subcutaneous tissue do not regenerate and are replaced by a scar (arrow).
(Illustration by Cyndie C. H. Wooley.)
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.