In some cases surgery
can be motivated by more than simply an improvement in appearance. Older
patients in particular may have eyelids so pendulous that they interfere
with vision, and old patients may also have such poor skin elasticity that
the lower eyelid gapes away from the eyeball, resulting in chronic conjunctivitis
and a constant flow of tears. To correct this, the lower eyelid has to be
stretched and lifted.
The anatomy of the eyelid
The skin of
the eyelid is the thinnest skin on the body. The dermis is less than a millimeter
thick, and immediately below it is the flat, ring-shaped orbicularis oculi
muscle that closes the eye.
This thin skin heals
better than the skin on any other part of the body. Sometimes, if the scar
follows a natural crease on the eyelid, it is virtually impossible to even
see it. On some patients the scar may be visible as a thin white line.
Beneath the orbicularis muscle is a thin membrane, the septum orbitale,
and beneath this is fat. The muscle that opens the eye (levator) is in the
upper eyelid beneath this cushion of fat. This muscle is fastened to a cartilage
band that extends from the edge of the eyelid about half a centimeter up
into the eyelid. In the lower eyelid this band is only a few millimeters
wide. The skin of the upper eyelid is attached to the levator muscle, which
causes the crease in the upper eyelid when the eye is open. This crease
(the supraorbital crease) is very different on different individuals. Asiatic
people, for example, have a poorly defined supraorbital crease and may lack
it entirely. Others have a supraorbital crease that is quite pronounced.
Behind these structures is the eye itself, which
is supplied with blood and nerves from the back of the eye socket. The muscles
that move the eye are attached to the eyeball and lie on its surface. The
nerves to the muscle that close the eye are small branches of the facial nerve
(facialis), which enter the orbicularis muscle at its lower and outer edges.
