What is Aqueous Humor? – Functions and Composition

In medicine, humor refers to a fluid (or semi-fluid) substance.

Therefore, aqueous humor is the fluid normally present in the front and back chambers of the eye. It is a clear and fluid flow that flows and nourishes the cornea; It is secreted by the ciliary processes.

The aqueous humor is a transparent, aqueous liquid similar to plasma, but containing low concentrations of proteins.

It is secreted from the ciliary epithelium. It fills the anterior and posterior chambers of the eye and should not be confused with the vitreous humor , which is found in the space between the lens and the retina, also known as the posterior cavity or vitreous chamber.

What is its composition?

  • Amino acids: transported by the ciliary muscles.
  • 98% water
  • Electrolytes
  • Ascorbic acid.
  • Glutathione
  • Immunoglobulins

The term “humors” was part of an ancient theory that health came from the balance between body fluids.

These liquids were called humors. The disease arose when there was an imbalance between the humors. The humors were:

  • Phlegm (water).
  • Blood.
  • The black bile that is believed is secreted by the kidneys and spleen.
  • Yellow bile secreted by the liver.

This theory (which was variously called humoral theory, humoralism, and humor) was devised before Hippocrates (c.460-c.375 BC).

It was not definitively demolished until Rudolf Virchow published his formative book, Cellular Pathology, in 1858, which established the cellular basis of pathology.

The current pathology rests on a cellular and molecular basis. The humors have been dissipated, except for the aqueous humor.

What is the function of aqueous humor?

Without becoming too technical, the aqueous humor is continuously produced by the ciliary processes (located in the anterior chamber near the lens of the eye).

To function as it should, production must be balanced by draining at an equal rate.

Even small variations in the production or output of aqueous humor are significant, because they will have a great influence on intraocular pressure.

It carries vitamin C in the front segment to act as an antioxidant agent.

When the intraocular pressure increases, it can lead to glaucoma , an important cause of vision loss.

The aqueous humor provides a clear and colorless medium between the cornea and the lens and constitutes an important component of the eye’s optical system.

The aqueous humor is secreted by the ciliary epithelium that covers the ciliary processes and enters the posterior chamber.

Initially, to reach the posterior chamber, the various constituents of the aqueous humor must cross the three tissue components of the ciliary processes: the capillary wall, the stroma and the epithelial bilayer.

The main barrier for transport through these tissues is the cell membrane and those related to the complexes of attachment of the non-pigmented epithelial layer.

Circulating aqueous humor flows around the lens and through the pupil into the anterior chamber.

Within the anterior chamber, a temperature gradient creates a convective flow pattern, which is down near the cornea where the temperature is colder, and up near the lens where the temperature is warmer.

Maintains intraocular pressure and inflates the eyeball. It is this hydrostatic pressure that keeps the eyeball in an approximately spherical shape and keeps the walls of the eyeball tense.

Provides nutrition (eg, amino acids and glucose) for vascular eye tissues; Posterior cornea, trabecular mesh, lens and anterior vitreous.

It can serve to transport ascorbate in the anterior segment to act as an antioxidant agent.

The presence of immunoglobulins indicates a role in the immune response to defend against pathogens.

It provides inflation for the expansion of the cornea and, therefore, greater protection against dust, wind, pollen grains and some pathogens.

It works for the refractive index.

How is aqueous humor produced and drained?

The main structures of the eye related to the dynamics of aqueous humor are the ciliary body (the site of aqueous humor production), and the trabecular meshwork and the uveoscleral pathway (the main locations of aqueous humor flow).

The aqueous humor is secreted in the posterior chamber by the ciliary body, specifically the non-pigmented epithelium of the ciliary body (pars plicata).

It flows through the narrow slit between the front of the lens and the back of the iris, to escape through the pupil in the anterior chamber, and then drain out of the eye via the trabecular meshwork.

From here, it drains into Schlemm’s canal in one of two ways: directly, via venous via the episcleral vein, or indirectly, through collecting channels to the episcleral vein by intrascleral plexus and finally to the veins of the orbit.

5 alpha-dihydrocortisol, an enzyme inhibited by 5-alpha reductase inhibitors, can participate in the production of aqueous humor.

Recently, ocular lymphatics have been implicated in the outflow of aqueous humor. In addition, it is now understood that the trabecular meshwork is a complex organization of structures, which are controlled by various biomechanical and biochemical mechanisms.

Among others, the actinomyosin cytoskeletal system, the extracellular matrix, the intracellular signaling responses mediated by protein kinase C, Rho / Rho kinase and other biological factors are included.

This review will describe the various physiopathological mechanisms involved in the dynamics of aqueous humor.

Your drainage

The aqueous humor is continuously produced by the ciliary processes and this rate of production must be balanced by an equal rate of drainage of the aqueous humor.

Small variations in the production or exit of aqueous humor will have a great influence on intraocular pressure.

The drainage path for the flow of the aqueous humor is first through the posterior chamber, then the narrow space between the posterior iris and the anterior lens (contributes to a small resistance), through the pupil to enter the anterior chamber .

From there, the aqueous humor leaves the eye through the trabecular meshwork in Schlemm’s canal (a channel in the limbus, that is, the junction of the cornea and the sclera, which surrounds the cornea) flows to through 25-30 collecting channels in the episcleral veins.

The greatest resistance to aqueous flow is provided by the trabecular meshwork (especially the juxtacanalicular part), and this is where most of the aqueous flow occurs.

The inner wall of the canal is very delicate and allows the fluid to leak due to the high pressure of the fluid inside the eye.

The secondary route is the uveoscleral drainage, and it is independent of the intraocular pressure, the aqueous one flows through here, but to a lesser extent than through the trabecular meshwork (approximately 10% of the total drainage, while through the trabecular meshwork 90 % of total drainage).

The fluid is normally 15 mmHg (0.6 inHg) above atmospheric pressure, so when a syringe is injected the fluid flows easily.

If the fluid is leaking, due to the collapse and wilting of the cornea, the hardness of the normal eye is therefore corroborated.

The aqueous humor fills the anterior and posterior chambers of the eye. It is one of the fundamental components to ensure that optical physics and the health of your eyes are properly maintained.

The continuous production of aqueous humor is fundamental to the shape, size and quality of the image that your eyes can provide.