What is the Umor Acqueo
The aqueous humor (or aqueous humor) is a colorless and transparent liquid contained in the anterior segment of the eye. It is formed by secretion from the ciliary body and is mainly made up of water, salts and protein substances. Cellular elements, on the other hand, are almost absent.
The aqueous humor acts as a refractive medium (optical function) and supplies nutrients to the cornea and crystalline (nutritional function). In addition, it helps maintain intraocular pressure (static function).
The eye chambers
The eyeball is a closed, spherical anatomical structure, hollow inside.
Crystalline and ciliary body separate the eye into two cavities filled with liquid, one anterior and one posterior:
- The anterior cavity, smaller, can in turn be divided into two chambers (anterior: between cornea and iris; posterior: bordering on the crystalline and the ciliary body), both containing aqueous humor (liquid).
- The posterior cavity occupies, instead, about four fifths of the entire eyeball; it extends from the posterior face of the crystalline lens to the retina and contains the vitreous, gelatinous and transparent body (for this reason, the posterior cavity is also called the vitreous chamber).
Both the vitreous body and the aqueous humor contribute to stabilize the shape and position of the eye.
Features and properties
The aqueous humor occupies the space included in the anterior cavity of the eyeball. Produced by the ciliary body, it consists mainly of water, in which protein substances and minimal quantities of salts are dissolved. In the aqueous humor, amino acids, chlorides, hyaluronic acid, glucose and ascorbic acid are present in particular. Furthermore, very rare lymphocytes can be found, the number of which increases considerably during inflammatory processes of the eye. The pH is slightly alkaline (7.22).
Functions
The aqueous humor performs multiple functions:
- He participates in the refraction process, being one of the dioptric means of the eyeball;
- It helps to give consistency and volume to the eye and stabilizes the shape of the cornea, thanks to the pressure it exerts on the internal walls (physiological ocular tone);
- It has a nutritional function towards the lens and the cornea (ocular structures without vessels);
- Its task is to keep the lens intact and transparent;
- Prevents the cornea, crystalline lens and iris from sudden changes in temperature;
- It has a fundamental role in the regulation of intraocular pressure.
Dynamics of aqueous humor
The aqueous humor is a liquid that circulates continuously within the eye. In this way, it acts as a transporter of metabolites and waste substances.
The aqueous humor is produced by the secretive and filtering activity of the ciliary body (a portion of the middle or uve tunic of the eyeball, located behind the iris).
The flow of aqueous humor is made possible by the difference in pressure existing between the liquids inside the eye (which is normally around 14-20 millimeters of mercury) and that in the episcleral veins (about 9-13 mm Hg).
Production
The aqueous humor is formed as an interstitial fluid, mainly by mechanisms of active secretion: it passes through the epithelial cells of the ciliary processes and pours into the posterior chamber. From this it passes, passing the pupil, into the anterior chamber (space between the cornea and the iris), where it is reabsorbed. A minor productive path takes place for the ultrafiltration of the plasma at the level of the capillaries of the ciliary body.
resorption
Most resorption occurs in the anterior chamber, mainly at the edge of the iris. Stressed by intraocular pressure, the aqueous humor passes through the progressively smaller pores that make up the trabecular network, located between sclera and cornea, and enters the Schlemm canal (or venous sinus of the sclera). This last element constitutes an outflow towards the venous circle of the eye. In fact, the Schlemm canal communicates with the episcleral veins. Resorption by this pathway therefore depends on the gradient of intraocular pressure.
Aqueous mood and ocular tone
The rate of production and reabsorption of aqueous humor is accomplished in order to determine a pressure between 10 and 21 mmHg (normal range) within the eye. To maintain this stable value, the eyeball continuously produces a small amount of aqueous humor, while an equal level of this liquid is drained through a complex network of cells and tissues, located in the anterior chamber, near the ciliary body.
However, considering that the aqueous humor is a continuously renewed and circulating liquid, intraocular pressure is not an unchanging constant. Excessive production of aqueous humor or an obstacle to its outflow may cause ocular hypertension, a condition that predisposes to the onset of glaucoma (a subtle ocular disease that compromises the visual function following a suffering of the optic nerve). Furthermore, there are pathological alterations characterized by hypotonia, due to a lower production of aqueous humor or excessive drainage.
Aqueous humor and glaucoma
In the eye affected by glaucoma, excessive production or an obstacle to the outflow of the aqueous humor produce an increase in intraocular pressure. The compression of the tissues inside the eyeball that follows begins insidiously to alter the optic nerve and, over time, causes the progressive reduction of sight and visual field.
Numerous other risk factors are associated with glaucoma: advanced age, familiarity with the disease, belonging to the African-American race, high myopia, reduced central corneal thickness and circulatory changes, such as those caused by hypertension systemic and diabetes. Previous ocular trauma and the continued use of corticosteroids (eye drops, ointments or systemic drugs) can also contribute to causing or aggravating glaucoma.
Glaucoma is often called the " silent thief of sight ", since in most cases the disease progresses unnoticed, without causing obvious symptoms. The patient is aware of the disease only at an advanced stage, when the visual function is now irreversibly compromised.
The most frequent form of glaucoma, called chronic simple (open angle), occurs following the progressive narrowing of the outflow pathways of the aqueous humor. Mostly, it is asymptomatic, but some signs may lead to the suspicion of an increase in ocular tone: headache, rapid decrease in visual acuity, blurredness and alterations of the visual field (eg halos around lights).
Acute (closed-angle) glaucoma, on the other hand, can suddenly manifest itself with a pain around and inside the eyeball, so intense as to induce nausea and vomiting. This form is caused by a reduced width of the angle between the iris and the cornea ("lower anterior chamber").
There is also a form of congenital glaucoma, in which the drainage system, from birth, does not allow the regular outflow of aqueous humor. The resulting increase in intraocular pressure causes photophobia (light discomfort) and tearing in the child.
The "asymptomatic" progression of the disease can be avoided by periodic visits of the ophthalmologist, which allow an effective and personalized therapeutic strategy to be set up early. Glaucoma is usually treated with the use of hypotonizing eye drops to be instilled in the eye with regularity and continuity, to maintain constant pressure over 24 hours. If this approach proves insufficient, it is also possible to resort to laser surgery or surgical therapy, in such a way as to restore the normal outflow of aqueous humor.
