Anatomy of the Eyelids and Orbit

Before some of the common problems are discussed, it is important to understand the anatomy of the structures around the eyeball. The delicate structure of the eyeball is protected, against injury, on the sides and in front by bony walls of the orbit and eyelids respectively.

The orbit is the bony cage or the socket in the skull, which houses the eye. In front of the eye, the eyelids open and close by reflex or voluntary action to distribute tear fluid so as to keep the cornea (the front surface of the eye) moist, to shut out light, and to protect the eyes from foreign bodies and exposure. The outer surface of the lids is a layer of skin continuous with the skin of forehead above and that of the cheeks below. The outer layer of the lids contain muscles that elevate and lower the lids, a firm tissue plate, or tarsus, that maintains their shape, and eyelashes that prevent perspiration or small foreign bodies from entering the eye and damaging the transparent sensitive surface of the cornea. The inner surface of the lids is lined by a mucous membrane called the conjunctiva; this is continuous with the conjunctiva covering the white of the eyeball. The conjunctiva has a rich supply of blood vessels, which accounts for the bloodshot appearance of the eye after irritation. It also contains lubricating glands that permit the lids to move easily and the eye to rotate smoothly. Behind the upper eyelids are present the main tear-producing glands (the lacrimal glands).

The orbit contains, apart from the eyeball, nerves, blood vessels, fat, eye-muscles (to move the eyes freely and harmoniously in both directions), and the optic nerve, which transmits visual sensation from the eye to the brain. The orbit also forms the wall to the adjacent sinuses, which are air spaces in the skull lined by the same kind of membrane as the nose. Canals connecting the eyelids to the sinuses (Lacrimal system) allow secretions and tears to drain through the nose. Some of the problems frequently encountered by an Oculoplastic surgeon include: