Eyelid Anatomy and Physiology

ANATOMY AND PHYSIOLOGY OF THE EYELID

two musculomembranous veils located in front of the eyeball, which can be placed in contact with each other or separated to leave a more or less large part of the anterior face of the eyeball free. The upper eyelid is taller and more mobile than the lower eyelid.

Anterior side:

It is convex when the patches are in contact. Molded on the eyeball, it is covered by the skin.

Posterior Side:

It is concave, lined by a mucosa (laconjuntiva), and is molded on the globe.

Ends:

The two eyelids are joined at their ends by two commissures, the medial, slightly salient, and the lateral, more elongated and prolonged by the "wrinkles" that accentuate with age (crow's feet.

In pathologies the palpebral free edge should be examined well, we will find the glands that are more towards the periphery, the ducts.

ARTERIES:

The eyelids are very vascularized formations. Each of them has a main artery: upper palpebral and lower eyelid, branches of the ophthalmic. They anastomose in the lateral part.

VEINS:

They form two networks, a retrotarsal or subconjunctival network, which ends in the ophthalmic vein, and a pretarsal network that ends laterally in the superficial temporal vein and medially in the facial vein.

LYMPHATIC:

They are arranged in a pretarsal and a retro-tarsal network. The lateral ones go to the gangliospreauriculares and parotídeos, and the medial ones follow the facial vein and finish in the submandibular ganglia

NERVES:

The sensitive fillets come from the nerves: infratrochlear, lacrimal, medial branch of the supraorbital and supraorbital nerves, and lateral branches of the supraorbital and infraorbital nerves.

FUNCTION OF THE EYELID:

Lubricate anterior segment of the eye

Protect the eye from external traumas.

 EYELASH FUNCTION:

 Prevents dust from entering the eyeball

Form shadow, to regulate the amount of light that penetrates our eyes

MOVEMENT OF THE EYELIDS:

The movements of the eyelids can be described generically as opening and closing. The opening of the eyelids depends on the levator muscle of the upper eyelid, the retractor muscles of the lower eyelid and the smooth muscles of Müller. The closure of the same is due to the action of the orbicular muscle circumferentially surrounding the spinepalpebral.

Opening:

The contraction of the levator muscle of the upper eyelid produces its elevation, so this muscle is also called the main retractor of the upper eyelid. This effect takes place against the force of gravity.

With age, sometimes the aponeurosis of the levator is separated from its tarsal insertion, which leads to the appearance of ptosis. However, the skin fixation remains intact, which increases the depth of the eyelid fold.

Closing:

The main muscle that makes the extension of the eyelid is the orbicular, innervated by the VII cranial nerve. It is the main responsible for closing the eyelid and blinking. Anatomically it is divided into three parts: pretarsal, preseptal and orbital. The closure of the patches can be classified as blinking, guillo and spasm. The pretarsal and preseptal parts of the orbicular muscle are responsible for the flapping reflex and the unforced closure of the eyelids. The orbital portion is necessary for the forced closure.

Types Of eyelid movements:

There are three types of eyelid movements: spontaneous, reflex and voluntary

Spontaneous:

 It is the most frequent, its precise mechanism has not been determined, in some studies it has been shown that the preliminary movement is the contraction of the orbicularis muscle that the levator relaxation of the upper eyelid. The closing of the eyelids takes place from the outer edge toward the internal. Blink reflex is induced by sensory stimuli, which can be of different types, such as skin friction, auditory signals, visual stimuli with bright light and corneal or ocular irritation.

Reflection:

It is induced by sensory stimuli, which may be of different types, such as the cutaneous, auditory signals, visual stimuli with bright light and corneal uocular irritation. The presence of unexpected or threatening objects gives rise to the flicker (threat reflex), which requires a cortical participation, while the flicker in response to the essubcortical light.

voluntary:

To complete this movement it is necessary the participation of the preseptal and pretarsal portions of the orbicular muscle. One form of voluntary blinking is the wink, which represents a learned response in which bilateral dissociation of the closure of the eyes takes place (ie, only one of them is closed). This movement requires simultaneous contraction of the orbital and palpebral portions. of the orbicular muscle.