The aqueous humour: how is it involved in glaucoma

The term aqueous humour indicates a transparent liquid (composed mostly of water and a minimum amount of salts and proteins) located in the anterior chamber of the eye (that is, between the cornea and the lens) which is formed thanks to the secretion mechanisms of the ciliary body.

The structure of the eyeball

To better understand how to operate, it is necessary to understand the anatomical structure of the eyeball. The latter has a spheroidal shape with has a cavity inside it. The ciliary body (on one side) and the lens (on the other) separate the eye into two distinct cavities (one anterior and one posterior), inside which the liquid is contained:

The anterior cavity is the smallest and, in turn, can be divided into two additional chambers:

• anterior chamber: between cornea and iris;
• posterior chamber: between the crystalline and ciliary body.

The posterior cavity covers most of the surface of the eyeball.

In this video posted by Rome vision clinic, the ocular structure is explained in detail.

The functions of the aqueous humour

One of the functions of this liquid is to contribute to the stability of intraocular pressure. This mild pressure that the liquid Imprints on the inner wall of the cornea helps in keeping our eyeball shape.

This liquid plays a leading role in the refraction mechanisms of the eye, being the second transparent medium.

Another function performed is that of nutrition, the aqueous humour contributes to the nourishment both of the cornea and of the crystalline.

It also has function as a protection of the iris, cornea and crystalline from strong temperature changes.

Production and reabsorption

As we previously described, this liquid is generated by the mechanisms of active secretion. The rhythm of production (which starts in the epithelial cells of the ciliary processes to then flow into the posterior chamber) and reabsorption (which takes place in the anterior chamber, after the liquid has passed first into the posterior chamber) maintains stable eye pressure between 10 and 20 mm of mercury (mmHg).

The Schlemm Canal

This element allows for communication between the anterior episcleral and ciliary veins, which represents an outflow track towards the ocular venous circle.

Aqueous humour and glaucoma

An alteration in the outflow of aqueous humour can generate glaucoma, and, consequently, an increase in intraocular pressure. This leads to a damaging compression of the tissues inside the eyeball and a progressive reduction of both vision and visual field.

Bibliography

1. IAPB Italia ONLUS | Parti dell’occhio Umor acqueo. Ottobre 2013