Eyebrows: Functions and Diseases

Introduction

The eyebrows are arched cutaneous-muscular reliefs, which correspond approximately to the profile of the upper bone edge of each of the two orbital cavities. More precisely, the superciliary arches surmount the frontal bone with a thick skin layer provided with hairs, glands sebaceous and sweat.
The function of the eyebrows is mainly to protect the ocular surface, as they prevent sweat from the forehead from reaching it.
The eyebrow arches can be affected by localized or systemic diseases, which cause them to thin out and fall (alopecia) or change their pigmentation.


Features

The eyebrows are two raised cutaneous-muscular formations with a curved shape with a lower concavity.
The two superciliary arches are symmetrically located between the forehead and the upper eyelid, near the frontal projections of the frontal bone, and are separated at the root of the nose by a generally poor or hairless area, called the glabella.
The skin layer of the eyebrow arch (visible) is covered with stiff and short hair, dense and obliquely arranged (with the tip facing laterally).
From the midline of the nose to the temple, it is possible to distinguish in each eyebrow, a head, a body and a tail, which corresponds to the thinnest end of the arch.


Note. The arrangement of the hair of the eyebrows responds to numerous individual and racial variations. Their growth cycle lasts from one to six months.


In the area of ​​the eyebrows, below the skin surface, there is a subcutaneous and a muscular layer, composed of its own fibers (eyebrow corrugator) and fibers deriving from other facial muscles (temporal and orbicular).
The deep surface of the eyebrows, on the other hand, is made up of a periosteum (connective and rich in fat) adhering to the frontal bone.
The eyebrows are supplied by the branches of the ophthalmic artery and the superior ophthalmic vein.

Functions

The eyebrows are ocular appendages, that is, secondary structures that support visual function; together with the eyelids, conjunctiva and lacrimal ducts, they constitute the protective apparatus of the eye.
The eyebrows also represent a very important element as regards the somatic characteristics of the individual and facial expressions.

Ocular surface protection

The protective function of the eyebrows is mainly to prevent sweat from the forehead from reaching the eyes. Furthermore, the eyebrow arches protect the anterior ocular surface from direct light from above.


Note. If the eyebrow arch were missing, the dripping of sweat into the eye would cause a very strong burning and a temporary inability to see.

Facial mimic

In the area of ​​the eyebrow arches, the fibers of the frontal mimic muscles, orbicularis of the eye and corrugator of the eyebrow run in depth. This gives the eyebrows a lively mobility in the facial expressions and a synkinesis (contemporaneity of the movements) in the exaggerated opening of the eyelids.

Diseases of the eyebrows

Thinning and dropping of the eyebrows is a localized form of alopecia, sometimes referred to as "madarosis", which can occur at any age. This can represent an isolated event or a symptom of numerous systemic diseases.
The factors that predispose to the problem include severe mental stress, deficiencies and / or eating disorders (such as anorexia), infections of the periocular region (folliculitis caused by bacteria, fungi or parasites) and systemic (syphilis and trachoma), autoimmune diseases (eg . systemic lupus erythematosis) and endocrine diseases, such as hypothyroidism.
The thinning of the eyebrows can also result from allergic causes, eczema or atopic dermatitis, psoriasis and seborrhea. In particular, seborrheic dermatitis frequently affects the medial angle of the superciliary arch causing the typical appearance of greasy yellow scales on an erythematous base.
Alopecia can also depend on traumatic causes, such as habitual rubbing or hair pulling due to neurosis and tics (trichotillomania). Rarely, the problem depends on infiltrating local tumors or severe psychiatric imbalances. The eyebrows are affected, then , the effects of radiotherapy and various chemotherapy pharmacological protocols.
The pathological conditions affecting the eyebrows also include poliosis (localized depigmentation of eyelashes and eyebrows), vitiligo, scabies and eyelid phthyriasis, an expression of lice infestation of eyelashes and eyebrows.


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