- Aqueous humor is a clear, watery fluid that fills the anterior and posterior chambers of the eye—the spaces between the cornea and the lens.
- It plays a critical role in maintaining intraocular pressure (IOP), nourishing avascular ocular tissues, and removing metabolic waste. Produced continuously by the ciliary body in the posterior chamber, aqueous humor circulates through the eye in a carefully regulated flow that is vital to ocular health and visual function.
- The aqueous humor is composed mainly of water, along with small amounts of electrolytes, glucose, amino acids, and vitamin C. Unlike blood plasma, it is low in protein to maintain its transparency, ensuring it does not interfere with the transmission of light through the eye. After being secreted by the non-pigmented epithelium of the ciliary processes, the fluid flows from the posterior chamber through the pupil into the anterior chamber. From there, it drains primarily through the trabecular meshwork and into Schlemm’s canal, eventually reaching the episcleral veins. A smaller portion exits through the uveoscleral pathway, which involves diffusion through the ciliary muscle into the suprachoroidal space.
- One of the most vital functions of aqueous humor is to maintain the eye’s intraocular pressure, which helps preserve the globe’s shape and provides a counterbalance to external forces. Stable IOP is essential for the proper alignment and function of the optical components of the eye. Additionally, aqueous humor delivers oxygen and nutrients—such as glucose and ascorbate—to the cornea and lens, both of which lack their own blood supply. It also helps remove carbon dioxide and metabolic waste from these structures, contributing to their transparency and function.
- Disruption in the production or outflow of aqueous humor can lead to serious eye conditions. The most notable of these is glaucoma, a group of diseases characterized by increased intraocular pressure due to impaired drainage. Prolonged elevation of IOP can damage the optic nerve, leading to progressive and irreversible vision loss. Treatment for glaucoma often targets the reduction of aqueous humor production (using beta-blockers or carbonic anhydrase inhibitors) or the enhancement of its outflow (via prostaglandin analogs or surgical procedures).
- Aqueous humor also plays a role in immunological defense, serving as a medium that contains immunosuppressive factors to prevent inflammation in the anterior segment. This contributes to what is known as immune privilege in the eye, where immune responses are tightly regulated to protect delicate tissues from inflammatory damage that could impair vision.
- In ophthalmology, aqueous humor can be sampled through a procedure called anterior chamber paracentesis, typically used to diagnose certain infections, inflammatory diseases, or malignancies of the eye. Research into its composition also contributes to the development of targeted therapies for ocular hypertension and inflammatory conditions.
