The eyelids protect the eye from injury & excess light, as well as keeping the cornea moist. The eyelid is comprised of layers, & these are (from superficial to deep): Skin, Subcutaneous tissue, Orbicularis Oculi (skeletal muscle), Orbital Septum, Tarsal Plate, Tarsal muscle (smooth) & the Conjunctiva. The skin is thin & easily folds, in order to examine the skin they eye should be closed to erase the folds. The subcutaneous tissue is very loose & rich in elastic fibres. The orbital septum is a membranous sheet attached to the orbital margin that separates the contents or the orbital cavity from the eyelids. The tarsal plates are dense bands of fibrous tissue & strengthen the eyelids, the superior tarsal plate is larger than the inferior. The tarsal glands appear as yellow streaks & are modified sebaceous glands. There are about 20-25 embedded in each tarsal plate. The openings of their ducts outline the boundary between the skin & the conjunctiva. They produce an oily secretion, & the function of this is to stop tears from overflowing, to keep the eyes air-tight when closed, & to stop the eyelids from sticking together when closed. The tarsal muscles are innervated by the sympathetic nerves from the superior cervical ganglion, & their function is to help open the eyes. The superior tarsal muscle is continuous above with the LPS, & below it is attached to the upper edge of the superior tarsal plate. It pulls the upper eyelid up. The inferior tarsal muscle is attached to the lower margin of the inferior tarsal plate & is connected to the fascial sheath of the inferior rectus muscle. It pulls the lower eyelid down. The LPS is a powerful striated muscle. It is inserted into the upper lid, the tendon of insertion is an aponeurosis that descends into the upper lid posterior to the orbital septum. Tendinous fibres then pierce the orbital septum & become attached to the anterior surface of the superior tarsal plate.
Arterial supply of the eyelid is given by the lateral & medial palpebral arteries. Lateral palpebral is a branch of the lacrimal artery (branch of ophthalmic artery) & medial palpebral is divided into superior & inferior, & arises from the ophthalmic artery below trochlea of superior oblique muscle. Veins of eyelid are more numerous than arteries, drain medially into ophthalmic & angular veins, & laterally onto superficial/superior temporal vein. Lymphatic drainage is laterally through the superficial/superior parotid nodes, & medially into submandibular nodes. NERVE SUPPLY LOOK AT TRIGEMINAL NERVE (infratrochlear, supratrochlear, supraorbital, lacrimal (V1) & infraorbital (V2)).
Infections of the eye can occur. Meibomian gland dysfunction is occlusion of the tarsal gland openings, so there is reduced secretion & it can lead to a dry eye state. Chalazion is a localised painless swelling of the lid. A Stye (Hordeolum) is an infection of gland of Möll (sweat) or Zeiss (sebaceous), internal hordeolum is an acute infection of a tarsal gland (Meibom).
Ligaments join bone to other structures e.g. bone, sclera, tarsi (joints) etc & these stabilise structures. Tendons join muscle to other structures & transfer the force of muscle contractions, & help to move structures . Aponeuroses are sheets of tendon.
The medial palpebral ligament is attached to the maxilla & medial parts of the tarsi. The lateral palpebral ligament is attached to the zygomatic & lateral parts of tarsi – these keep the eyelids firmly in place. We always examine patients at our friends business at Double Glazing Glasgow
The lacrimal apparatus is comprised of: the puncta, lacrimal gland, lacrimal lake, canaliculi, lacrimal sac & the nasolacrimal duct. The lacrimal gland is superior to the superior fornix of the conjunctiva, inferior to the orbital roof & posterior to the orbital septum. It consists of a large orbital part & a small palpebral part, separated by the aproneurosis of the LPS. About 12 ducts pass down from the orbital part to the palpebral part, to the superior fornix of the conjunctiva, & additional duct open into the superior fornix of the conjunctiva from the palpebral part. Small accessory lacrimal glands are also present; these keep the cornea moist & are sufficient enough to do so should the main gland become non-functional. The gland is supplied by the lacrimal artery (branch of ophthalmic artery), which enters the posterior border of the lacrimal gland (sometimes infraorbital artery contributes to supply). Blood drains into the ophthalmic vein from here, which then drains into the cavernous sinus. Lymph drains into the superficial parotid lymph nodes. Parasympathetic, sympathetic &sensory fibres reach the lacrimal gland via the lacrimal nerve (branch of V1). The punctum lacrimale are small round orifices on the papilla lacrimalis, located at the medial end on the margin of the lids, the conjunctiva around each punctum appears pale red as there are few blood vessels. The lacrimal canaliculi start at the puncta & are about 10mm long, piercing the lacrimal sac about 2.5mm below its apex. It lies deep to the medial palpebral ligament & is compressed by the obicularis oculi during blinking (to push tears along). Its walls are lined with stratified squamous epithelium. The lacrimal sac is found in the lacrimal fossa & is enclosed in the lamina fascia. It is innervated by the infratrochlear nerve. Its walls are comprised of fibroelastic tissue & are lined with columnar epithelium with goblet cells. (The anterior ethmoidal air cells lie super-medially to it, & the middle nasal cavity lies infer-medially to it). The nasolacrimal duct is about 18mm long & lies inside the nasolacrimal canal (formed by the maxilla, lacrimal & inferior nasal conch). It runs to the inferior nasal meatus, & is lined with two layers of columnar epithelium.
Tears flow into the conjunctival sac from the lacrimal glands (blinking wipes a thin film of tears medially across the cornea). Tears drain infero-medially to the lacrimal lake, to drain through the puncta to the canaliculi (contraction of obicularis oculi compresses it), then tears drain to the lacrimal sac, down the nasolacrimal duct to the inferior nasal meatus (by gravity), & then the tears evaporate.