Corpus: Orbital septum

The orbital septum is a fiber-rich layer of tissue that inserts at the orbital margin and merges seamlessly into the periosteum or periorbita.

The orbital septum functions like a circular membrane that enclose the orbit around the eyeball. In the upper eyelid, it is connected to the tendon of the levator palpebrae superioris muscle and the superior tarsus (upper part of the eyelid cartilage). In the lower eyelid, it attaches to the inferior tarsus (lower part of the eyelid cartilage). Medially, the orbital septum thins and attaches to the lacrimal sac, detaching from the medial palpebral ligament. It is pierced by blood vessels and nerves that travel from the orbit to the face and forehead, such as the lacrimal nerve.

The orbital septum is a critical boundary in bacterial infections of the soft tissues adjacent to the eye. Inflammation confined to the tissue in front of the orbital septum is called periorbital phlegmon, while inflammation located behind it is known as orbital phlegmon.