Embedded in the tarsal plates are tarsal glands (see Fig. 8.77), which empty onto the free margin of each eyelid. These glands are modified sebaceous glands and secrete an oily substance that increases the viscosity of the tears and decreases the rate of evaporation of tears from the surface of the eyeball. Blockage and inflammation of a tarsal gland is a chalazion and is on the inner surface of the eyelid.
The tarsal glands are not the only glands associated with the eyelids. Associated with the eyelash follicles are sebaceous and sweat glands (see Fig. 8.77). Blockage and inflammation of either of these is a stye and is on the edge of the eyelid.
The arterial supply to the eyelids is from the numerous vessels in the area (Fig. 8.81). They include: the supratrochlear, supra-orbital, lacrimal, and dorsal nasal arteries from the ophthalmic artery; the angular artery from the facial artery; the transverse facial artery from the superficial temporal artery; and branches from the superficial temporal artery itself.
Venous drainage follows an external pattern through veins associated with the various arteries and an internal pattern moving into the orbit through connections with the ophthalmic veins.
Lymphatic drainage is primarily to the parotid nodes, with some drainage from the medial corner of the eye along lymphatic vessels associated with the angular and facial arteries to the submandibular nodes.
Innervation of the eyelids includes both sensory and motor components.
The sensory nerves are all branches of the trigeminal nerve [V] (Fig. 8.82). Palpebral branches arise from: the supra-orbital, supratrochlear, infratrochlear, and lacrimal branches of the ophthalmic nerve [V1]; and the infra-orbital branch of the maxillary nerve [V2].
Motor innervation is from: the facial nerve [VII], which innervates the palpebral part of the orbicularis oculi; the oculomotor nerve [III], which innervates the levator palpebrae superioris; and sympathetic fibers, which innervate the superior tarsal muscle.
Loss of innervation of the orbicularis oculi by the facial nerve [VII] causes an inability to close the eyelids tightly and the lower eyelid droops away, resulting in a spillage of tears.
Loss of innervation of the levator palpebrae superioris by the oculomotor nerve causes an inability to open the superior eyelid voluntarily, producing a complete ptosis.
Loss of innervation of the superior tarsal muscle by sympathetic fibers causes a constant partial ptosis.
The lacrimal apparatus is involved in the production, movement, and drainage of fluid from the surface of the eyeball. It is made up of the lacrimal gland and its ducts, the lacrimal canaliculi, the lacrimal sac, and the nasolacrimal duct.
The lacrimal gland is anterior in the superolateral region of the orbit (Fig. 8.83) and is divided into two parts by the levator palpebrae superioris (Fig. 8.84):
The larger orbital part is in a depression, the lacrimal fossa, in the frontal bone.
The smaller palpebral part is inferior to the levator palpebrae superioris in the superolateral part of the eyelid.
Numerous ducts empty the glandular secretions into the lateral part of the superior fornix of the conjunctiva.
Fluid is continually being secreted by the lacrimal gland and moved across the surface of the eyeball from lateral to medial as the eyelids blink.