What is Aqueous Humor? – Functions and Composition

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

Therefore, aqueous humor is the fluid usually present in the front and back chambers of the eye. It is a clear and fluid flow that flows and nourishes the cornea; The ciliary processes secrete it.

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

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

These liquids were called humor. The disease arose when there was an imbalance in the humor. The humor was:

  • Phlegm (water).
  • Blood.
  • The black bile is believed to be secreted by the kidneys and spleen.
  • The liver secretes yellow bile.

This theory (which was variously called humoral theory, humoral, 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, establishing the cellular basis of pathology.

The current pathology rests on a cellular and molecular basis. The humor has 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 eye’s lens).

Production must be balanced by draining at an equal rate to function as it should.

Even slight variations in the production or output of aqueous humor are significant because they will significantly influence intraocular pressure.

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

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

The aqueous humor provides a clear and colorless medium between the cornea and the lens and constitutes an essential 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.

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 attachment complexes of the non-pigmented epithelial layer.

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

A temperature gradient within the anterior chamber creates a convective flow pattern, down near the corner where the temperature is colder and up near the lens where the temperature is warmer.

Maintains intraocular pressure and inflates the eyeball. This hydrostatic pressure keeps the eyeball in an approximately spherical shape and keeps the walls of the eyeball tense.

Provides nutrition (e.g., 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, more excellent 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).
  • The trabecular meshwork.
  • The uveoscleral pathway (the central location 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 drain out of the eye via the trabecular meshwork.

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.

Five 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 controlled by various biomechanical and biochemical mechanisms.

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 aqueous humor dynamics.

Your drainage

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

Slight variations in the production or exit of aqueous humor will significantly influence intraocular pressure.

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

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) and flows through 25-30 collecting media in the episcleral veins.

The trabecular meshwork provides the most significant resistance to aqueous flow (especially the juxtacanalicular part), 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 liquid inside the eye.

The secondary route is the uveoscleral drainage, 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 while through the trabecular meshwork, 90 % of total drainage).

The fluid usually is 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 cornea’s collapse and wilting, the normal eye’s hardness 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 adequately maintained.

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