Aqueous humor is a transparent, watery fluid found within the eye, similar in consistency to blood plasma but with a lower protein concentration. It is composed primarily of water, approximately 99.9%, with the remaining 0.1% consisting of various substances such as sugars, vitamins, and proteins. This fluid fills the front sections of the eye, playing a role in maintaining its structure and health.
Location and Circulation within the Eye
Aqueous humor is situated in two main areas of the eye: the anterior chamber and the posterior chamber. The posterior chamber is the space located between the iris, which is the colored part of the eye, and the lens. The anterior chamber lies in front of the iris, specifically between the iris and the cornea, the clear outer layer of the eye.
The production of aqueous humor begins in the posterior chamber by a structure called the ciliary body. This fluid then flows from the posterior chamber, through the pupil, and into the anterior chamber. From the anterior chamber, the aqueous humor is continuously drained from the eye primarily through a spongy tissue known as the trabecular meshwork. This meshwork allows the fluid to enter Schlemm’s canal, a circular drainage canal, which then carries the fluid into the episcleral venous system, where it is absorbed back into the bloodstream.
Function of Aqueous Humor
The aqueous humor performs several functions within the eye. One primary role is to maintain intraocular pressure (IOP), which helps to keep the eyeball inflated and in its spherical shape. This stable pressure is necessary for the eye’s optical components, like the cornea and lens, to function correctly.
The fluid also provides nourishment to specific eye structures that lack their own blood supply, such as the lens and the cornea. It delivers essential nutrients like oxygen and glucose to these avascular tissues. Aqueous humor is responsible for removing metabolic waste products from these areas, maintaining the health of the anterior segment of the eye.
When Aqueous Humor Goes Wrong
An imbalance in the production and drainage of aqueous humor can lead to increased intraocular pressure. This occurs either due to excessive fluid production by the ciliary body or, more commonly, impaired drainage through the trabecular meshwork, causing fluid to accumulate.
This buildup of fluid and subsequent increase in intraocular pressure is a primary factor in the development of glaucoma. Glaucoma is a group of eye conditions that can damage the optic nerve, the bundle of nerve fibers that transmits visual information from the eye to the brain. The sustained high pressure can directly injure the optic nerve or reduce blood flow to it, potentially leading to blind spots and, if left unaddressed, permanent vision loss.