Apparato palpebrale e Congiuntiva PDF

## Lez. III Palpebre **Our eye is protected by the eyelids which, due to a reflex, close quickly to protect it when faced with a blinding light or an object approaches the face too abruptly or touches the cornea (ocu-lo-palpebral reflex).** - The closing of the eyelids, involuntary or voluntary,...

## Lez. III Palpebre **Our eye is protected by the eyelids which, due to a reflex, close quickly to protect it when faced with a blinding light or an object approaches the face too abruptly or touches the cornea (ocu-lo-palpebral reflex).** - The closing of the eyelids, involuntary or voluntary, is called blinking; it also serves, among other things, to spread the tear fluid evenly over the surface of the eye, removing any dust or particles which may have entered the eye. - The eyebrows, which are fairly thick hairs that grow from two muscle-skin ridges located at the level of the upper margin of the orbit, are also attached to the eyelids, always acting as a protective function. - To describe the eyelids anatomically, imagine a kind of disc that closes the anterior part of the orbit; the disc is crossed horizontally by a thin opening, the palpebral fissure (from the Latin rima=fissure), which divides it into two parts: the upper eyelid and the lower eyelid. - The outside of the disc is covered by skin, the inside by the conjunctiva. - The palpebral fissure, bounded by the two free edges of the eyelids, represents the entrance to the conjunctival sac (see Lez. IV); the two ends of the fissure are called the inner canthus and the outer canthus. **The inner canthus surrounds the lacrimal lake, which is where tears collect before they enter the drainage system.** - A mucosal fold called the semilunar fold is visible here; at the bottom of this fold lies a small protrusion, the lacrimal caruncle (dim. of the Latin caro, carnis=small flesh). - The medial end of the free edge of each eyelid, where eyelashes are absent, has a funnel-shaped prominence called the lacrimal papilla. - The lacrimal papilla is pierced by the lacrimal punctum, which is the entrance to the lacrimal canal (see Lez. V), which is the starting point of the tear drainage system. **Microscopically, from the outside in, the eyelids are made up of three layers,** in addition to the lining membrane formed by the conjunctiva, which will be discussed separately (Lez. IV): **Cutaneous layer - the eyelid skin is very delicate, thin and elastic and is attached to the underlying muscle tissue by a very loose connective tissue (from the Latin laxus=slack): these characteristics explain why edema (from the Greek oídēma=swelling) can occur even in widespread areas, and why, following trauma (from the Greek traûma=wound) that causes capillaries to rupture, blood very easily spreads into the tissues, forming ecchymosis (from the Greek enkhímosis=extravasation of blood), which causes the well-known “black eye”.** - At the edge of this cutaneous layer, eyelashes grow which are short and curved, arranged in two or three rows; the hair follicles of the eyelashes have attached sebaceous glands of Zeis and modified sweat glands of Moll (see Lez. V). ##### **Muscular layer - this is made up of the orbicularis oculi muscle, the levator palpebrae superioris muscle, and the Müller's muscle.** - **The orbicularis oculi muscle (from the Latin orbiculus=circle)** is composed of circular muscle fibers; it lies between the tarsus and the skin, and extends beyond the orbital margin. - It is innervated by the facial nerve (VII pair) and its function is to close the palpebral fissure. - The orbicularis oculi muscle fibers that run along the palpebral fissure, at the level of the free edge, are called the Riolan's muscle, while other fibers that surround the lacrimal sac and canaliculi are called the Horner's muscle: the former serves to keep the eyelid edges close to the eyeball, the latter to squeeze the canaliculi and sac to allow tears to drain. - **The levator palpebrae superioris muscle** attaches to the front surface of the tarsus at a high point, and is innervated by the oculomotor nerve (III pair); when it contracts, it pulls the upper eyelid upwards and backwards. - **The Müller's muscle** is composed of smooth involuntary muscle fibers, lies beneath the levator palpebrae superioris, and is innervated by the sympathetic nervous system; it gives tone to the eyelid and acts by an involuntary reflex mechanism in defensive or fearful reactions. ##### **Tarsal layer - the tarsus (from the Greek tarsòs=framework)** consists of a thin plate of dense fibrous tissue, giving it its structure. Embedded within it are rows of Meibomian glands, lying in vertical parallel rows: these are long glands with a blind end that produce an oily secretion and have numerous lateral outgrowths. Their secretion is released onto the posterior edge of the free margin of the eyelids, through tiny mouths (from the Latin os, oris=mouth and facere=to make, i.e. it acts as a mouth) arranged immediately behind the line of eyelash growth. ## Lez. IV Congiuntiva - The conjunctiva is a thin transparent mucous membrane that lines the inside of the eyelids, and then covers the front of the globe, except for the cornea. - It is so named because it joins the eyelids to the eyeball. - It is made up of a superficial epithelial layer rich in goblet cells and serous lacrimal glands, an intermediate adenoid (from the Greek adén=gland) layer rich in lymphocytes, and a deep fibrous layer containing blood vessels and nerves. - The conjunctiva can be divided into three parts: - **Palpebral or tarsal**, which lines the inside of the eyelids; - **Of the fornices** (from the Latin fornix=arch, fold), encompassing the zone where it folds into a U-shape, both above and below; - **Bulbar**, which covers the front surface of the eyeball except for the cornea. - In the inner canthus of the eye, we can see two small formations, the caruncle and the semilunar fold. - The caruncle is a small, rosy protrusion with a structure similar to the epidermis, containing sebaceous glands and hair follicles, while the semilunar fold is a fold of conjunctiva shaped like a crescent which represents the remnant of a third eyelid that moves horizontally. - The conjunctiva is poorly supplied with pain endings, but is rich in blood vessels. - Due to these characteristics, it reacts to infections, toxins, and allergies with noticeable hyperemia (from the Greek haima=blood, increased blood flow) and swelling, while pain is barely present or limited to a burning sensation.