What is eye liquid called

The eye contains two distinct fluids—aqueous humor and vitreous humor—each with specific compositions, locations, and functions essential for maintaining eye health, optical clarity, and proper pressure. These fluids differ significantly in their properties and serve complementary roles in supporting vision.

Aqueous humor is a clear, watery fluid filling the anterior and posterior chambers—the spaces between the cornea and iris, and between the iris and lens respectively. This fluid is continuously produced by the ciliary body through a combination of active secretion and ultrafiltration from blood plasma, with production occurring at approximately 2-3 microliters per minute. Aqueous humor composition closely resembles blood plasma but contains less protein and more ascorbic acid (vitamin C) and amino acids, creating a carefully controlled environment for the avascular cornea and lens. The fluid circulates from the posterior chamber through the pupil into the anterior chamber, providing nutrients and oxygen to the lens and cornea while removing metabolic waste products. It then drains through the trabecular meshwork at the angle where the iris meets the cornea, flowing into Schlemm's canal and eventually returning to the bloodstream. This continuous production and drainage maintains intraocular pressure (IOP) typically between 10-21 mmHg, which is crucial for maintaining the eye's shape and proper optical function. When drainage is impaired or production exceeds drainage, IOP rises, potentially causing glaucoma—progressive optic nerve damage that can lead to vision loss.

Vitreous humor is a clear, gel-like substance filling the large posterior cavity behind the lens, comprising approximately 80% of the eye's total volume (about 4 milliliters in adults). Unlike aqueous humor, vitreous is not continuously replaced but is formed during embryonic development and remains relatively stable throughout life. Its composition includes approximately 98-99% water, with the remaining content consisting of collagen fibrils (primarily type II collagen), hyaluronic acid (a glycosaminoglycan providing gel-like properties), and small amounts of proteins, salts, and sugars. The precise arrangement of collagen fibers and hyaluronic acid molecules creates a transparent gel structure that allows light to pass through unobstructed while providing mechanical support to maintain the eye's spherical shape and keep the retina pressed against the back wall of the eye. The vitreous also serves protective functions, absorbing physical shocks and creating a reservoir of metabolites for the surrounding tissues.

With aging, the vitreous undergoes natural changes called syneresis, where the gel liquefies and collagen fibers clump together, potentially causing floaters—small shadows cast on the retina by these aggregated fibers that people perceive as spots or strands drifting across their vision. In some cases, vitreous shrinkage can cause posterior vitreous detachment, where the gel separates from the retina, usually benign but occasionally pulling on the retina strongly enough to cause tears or detachment requiring prompt treatment. Additional fluids contribute to eye health, including tears produced by the lacrimal glands and accessory glands, which form a protective tear film over the cornea consisting of three layers: an outer lipid layer preventing evaporation, a middle aqueous layer providing moisture and nutrients, and an inner mucin layer helping tears adhere to the eye surface. Understanding these various fluids and their functions helps explain numerous eye conditions and treatment approaches, from glaucoma medications that reduce aqueous production or increase drainage, to surgical procedures addressing vitreous complications.