Orbit and Ocular Adnexa
The rich blood supply to the eyelid skin supports rapid healing. Approximately the third day after an injury to the skin, myofibroblasts derived from vascular pericytes migrate around the wound and actively contract, decreasing the size of the wound. The eyelid and orbit are compartmentalized by intertwining fascial membranes that enclose muscular, tendinous, fatty, lacrimal, and ocular tissues; these tissues can become distorted by scarring. Exuberant contraction distorts muscle action, producing dysfunctional scars. The striated muscles of the orbicularis oculi and extraocular muscles are made of terminally differentiated cells that do not regenerate after injury, but the viable cells may hypertrophy.
The extraocular muscles are composed of 2 different types of muscle fibers: slow, tonic type and fast, twitch type. The ratio of nerve fibers to muscle fibers is very high, which allows precise movements of the eye. Each extraocular muscle attaches to the sclera at a specific anatomical location via a tendinous insertion, allowing coordinated movement of the eyes. As a response to injury or inflammation, strabismus may occur because of atrophy of the muscle belly itself or from scarring of the tendon to the sclera, which results in muscle restriction.
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.