Anatomy of eyelids and conjunctiva
The Eyelids
These are two movable folds of tissue situated above and below the front of each eye. There are short curved hairs, the eyelashes situated on their free edges. The layers of tissue which form the eyelids are:
- a) A thin covering of skin.
- b) A thin sheet of areolar tissue.
- c) Three muscles: the orbicularis oculi, levator palpebrae superioris and Muller’s muscle.
- d) A thin sheet of supporting dense connective tissue, the tarsal plate, larger in the upper than in the lower eyelid.
- e) A lining of palpebral conjunctiva.
The Lid Margin
It is divided into rounded anterior and sharp posterior borders by the grey line. The eyelashes originate anterior to the grey line and ducts of the meibomian glands are located posterior to the grey line. Grey line is important in operations where the lid is split as it indicates the position of loose fibrous tissue between the orbicularis muscle and the tarsus.
- Meibomian Glands (Tarsal Glands): These are modified sebaceous glands about 20 -30 in number embedded in the tarsal plate. They are directed vertically and open on the lid margin. Therefore, vertical incision is given while incising the chalazion.
- Zeis’s Glands: These are also modified sebaceous glands attached to the hair follicles.
- Moll’s Glands: These are modified sweat glands which open in the hair follicles or directly in the lid margin.
- Palpebral Fissure: The space between the two lids when the eye is open is known as the palpebral fissure or palpebral aperture.
- The Outer Canthus: The outer or lateral angle of the palpebral fissure is called the outer canthus.
- The Inner Canthus: The inner or medial angle of the palpebral fissure is called the inner canthus. A semilunar fold, the plica semilunaris with an elevation called the caruncle is situated in the inner canthus.
BLOOD SUPPLY: It is supplied by the ophthalmic and lacrimal arteries by their medial and lateral branches. The venous drainage is through the ophthalmic vein.
NERVE SUPPLY: The 7th nerve to orbicularis oculi muscle, 3rd nerve levator palpebrae superioris, sympathetic nerves supply to Muller’s muscle, sensory supply ophthalmic division of the 5th cranial nerve.
LYMPHATIC DRAINAGE: The preauricular and the submaxillary lymph nodes.