Aqueous Humor in Eye Anatomy

Aqueous humor is produced by the ciliary epithelium as a selective filtrate from capillaries of the ciliary body.

Aqueous humor flows from the posterior chamber, between the lens and iris, to the anterior chamber. It then drains through the trabecular meshwork into Schlemm's canal and into the aqueous vein.

Aqueous humor drains through two main routes: the trabecular meshwork and the uveoscleral route.

Ciliary epithelial cells are responsible for producing aqueous humor. They are divided into two types: nonpigmented epithelial cells (NPE) and pigmented epithelial cells (PE).

Nonpigmented epithelial cells (NPE) form a tight barrier that prevents movement of substances from the blood into the aqueous humor.

Aqueous humor is produced by filtering blood from the ciliary capillaries. This process involves water and solutes passing through a semipermeable membrane.

Ions are transported from the stroma through the ciliary epithelial cells into the posterior chamber. This transport requires specific transport proteins.

Water is transported from the stroma into the aqueous humor through the ciliary epithelial cells. Carbon dioxide reacts with water to form bicarbonate ions, which drives this process.

The aqueous humor plays multiple roles in maintaining a healthy eye. It nourishes the cornea, lens, and trabecular meshwork (TM) by supplying nutrients and oxygen. It also removes waste products from these tissues. Additionally, it maintains the eye's internal pressure (intraocular pressure or IOP) by inflating the eye, ensuring proper alignment of the optical structures. Further, it transports antioxidants and antibodies for protection against pathogens.

The aqueous humor primarily consists of water. It also contains a carefully regulated mixture of solutes transported from the blood plasma. These include ions, low molecular weight molecules, and high molecular weight molecules.

The aqueous humor contains ions that maintain its isotonicity, meaning it has the same osmotic pressure as the blood, preventing fluid shifts. Key ions include sodium, potassium, chloride, hydrogen, bicarbonate, calcium, and magnesium.

The aqueous humor contains essential low molecular weight molecules like nutrients (glucose, citrate, amino acids) and antioxidants (ascorbate, glutathione). It also carries waste products like lactic acid and urea.

The aqueous humor contains high molecular weight molecules like proteins (albumin, growth factors, enzymes), and signaling molecules (prostaglandins, cAMP, catecholamines, steroid hormones). The concentration of proteins is significantly lower in the aqueous humor compared to the blood plasma.

The aqueous humor provides essential nutrients for the cornea, lens, and TM. These nutrients include glucose for energy, citrate for energy production, and amino acids for protein synthesis.

The aqueous humor contains antioxidants such as ascorbate and glutathione, which protect the eye tissues from damage caused by free radicals.

The aqueous humor carries waste products such as lactic acid (produced during fermentation) and urea (produced during protein metabolism) away from the eye tissues.

Matrix metalloproteinases (MMPs) are enzymes that break down the extracellular matrix (ECM) in tissues. Increased IOP leads to upregulation of MMPs, ultimately degrading ECM.

When intraocular pressure (IOP) rises, it causes mechanical distortions in the eye. This triggers cells, such as trabecular meshwork cells, to release more MMPs. These MMPs then degrade the ECM, potentially leading to improved outflow.

Aqueous humor flows from the anterior chamber through the trabecular meshwork (TM) into Schlemm's canal (SC). It then moves into collector channels along the SC's outer wall before emptying into the episcleral and conjunctival veins on the scleral surface.

Muscarinic agonists activate muscarinic acetylcholine receptors on the ciliary muscle. This triggers muscle contraction, which displaces the Schlemm's canal (SC) endothelium, widening the spaces in the trabecular meshwork (TM). This allows more fluid to flow through.

Aqueous humor can flow from the chamber angle through the uveal layer of the trabecular meshwork (TM) into the connective tissue spaces between ciliary body muscle bundles. It then travels to the suprachoroid space, into the sclera or perivascular spaces, then into episcleral tissue, and finally into the venous circulation.

The process by which the fluid in the anterior chamber of the eye is produced. It originates from blood and moves through the capillary fenestrations into the stroma.

The Na+/K+ pump actively transports ions across the ciliary epithelium, creating an osmotic gradient that draws water and solutes into the anterior chamber.

These nutrients are actively transported from the stroma into the anterior chamber, providing vital nourishment to the eye's structures.

Proteins are actively transported from the stroma and synthesized by ciliary epithelial cells, contributing to the complex composition of the fluid.

The entire volume of aqueous humor is replaced every 90-100 minutes, highlighting its constant circulation.

Beta-blockers inhibit the effects of epinephrine, reducing the stimulation of aqueous humor production.

Stimulating alpha receptors (either with norepinephrine or alpha agonists) decreases aqueous humor production.

CAIs decrease the production of bicarbonate ions (HCO3-), which in turn reduces the flow of aqueous humor.