STRUCTURE OF EYELID
STRUCTURE
Each eyelid consists (from anterior to posterior) of the following layers
1. The skin.
It is elastic having the thinnest in the body.
2. The subcutaneous areolar tissue.
It is very loose and contains no fat. It is thus readily distended by oedema or blood.
3. The layer of striated muscle.
It consists of orbicularis muscle which forms an oval sheet across the eyelids. It comprises three por ions: the orbital, palpebral and lacrimal. It closes the eyelids and is supplied by zygomatic branch of the facial nerve. Therefore, in paralysis of facial nerve there occurs lagophthalmos which may be complicated by exposure keratitis.
In addition, the upper lid also contains levator palpebrae superioris muscle (LPS). It arises from the apex of the orbit and is inserted by three parts on the skin of lid, anterior surface of the tarsal plate and conjunctiva of superior fornix. It raises the upper lid. It is supplied by a branch of oculomotor nerve.
4. Submuscular areolar tissue.
It is a layer of loose connective tissue. The nerves and vessels lie in this layer. Therefore, to anaesthetise lids, injection is given in this plane.
5. Fibrous layer.
It is the framework of the lids and consists of two parts: the central tarsal plate and the peripheral septum orbitale.
i Tarsal plate.
There are two plates of dense connective tissue, one for each lid, which give shape and firmness to the lids. The upper and lower tarsal plates join with each other at medial and lateral canthi; and are attached to the orbital margins through medial and lateral palpebral ligaments. In the substance of the tarsal plates lie meibomian glands in parallel rows.
ii. Septum orbitale (palpebral fascia).
It is a thin membrane of connective tissue attached centrally to the tarsal plates and peripherally to periosteum of the orbital margin. It is perforated by nerves, vessels and levator palpebrae superioris (LPS) muscle, which enter the lids from the orbit.
6. Layer of non-striated muscle fibres.
It consists of the palpebral muscle of Muller which lies deep to the septum orbitale in both the lids. In the upper lid it arises from the fibres of LPS muscle and in the lower lid from prolongation of the inferior rectus muscle; and is inserted on the peripheral margins of the tarsal plate. It is supplied by sympathetic fibres.
7. Conjunctiva.
The part which lines the lids is called palpebral conjunctiva. It consists of three parts: marginal, tarsal and orbital.
OPTOMETRY-SHARP VISION
Optometrist