The sclera differs from the cornea in that its collagen fibers vary in thickness and are randomly distributed rather than laid down in orderly lamellae. As the sclera is relatively avascular and hypocellular, the episclera, when stimulated by injury, migrates into the scleral wound, supplying vessels, fibroblasts, and activated histiocytes. The final wound contracts, creating a puckered appearance. If the adjacent uveal tract (also called uvea) is damaged, uveal fibrovascular tissue may enter the scleral wound, resulting in a scar with dense adhesion between the uvea and the sclera. Indolent episcleral fibrosis produces a dense coat around an extrascleral foreign body such as an encircling scleral buckling element or a glaucoma tube shunt.
Because the wound healing processes in the cornea and sclera are relatively avascular, the tensile strength of wounds in these parts of the eye is less than that of the native, undisturbed tissue. In certain clinical situations, such as glaucoma filtering procedures, modifying the healing process through the use of topical antimetabolites such as 5-fluorouracil or mitomycin C may be desirable to prevent scar tissue from forming between the conjunctiva and the sclera at the surgical site (see BCSC Section 10, Glaucoma, Chapter 13). In keratoconus, modification of healing via collagen crosslinking is used in the cornea to prevent progressive thinning.
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.