The eyeball is divided into a posterior segment, encompassing most of the spherical back part of the eye where the retina is, and the anterior segment, which is up front and consists of the cornea, the iris and the lens, forming a posterior and anterior chamber. The anterior chamber is the space between the cornea and the iris of the eye. A transparent gelatinous nutrient liquid, the aqueous humor, fills the anterior segment and feeds the tissues that form the walls of the chamber.
The ciliary body located in the region where the lens attaches to the sclera, the outer surface tissue of the eye, secretes the aqueous humor into the posterior chamber, located between the iris and the lens. From the posterior chamber, the aqueous humor reaches and feeds nutrients to the anterior chamber through the pupil. Where the cornea meets the sclera, scleral veins are found; they remove waste products from the aqueous humor, delivering them into the bloodstream for removal from the body. In less than 24 hours, the ciliary body tissue replaces the aqueous humor in both the anterior and posterior chambers.
Enough aqueous humor is secreted into the anterior segment to maintain a healthy intraocular pressure (IOP) of about 10 millimeters of mercury (mmHg), or the pressure required to raise a column of mercury liquid in a capillary, or thin tube, 10 millimeters. Atmospheric pressure is 200 times the force per unit area of IOP, measured as the difference between atmospheric pressure and the pressure in the eye. More than twice the normal eye pressure results in glaucoma where IOP is great enough to damage the retina, resulting in blindness. This condition occurs if too much aqueous humor is produced, or not enough is removed, and is found to be related to high blood pressure. In some forms of glaucoma, the iris is up against the lens, closing off the posterior chamber and preventing the aqueous humor from getting to the anterior chamber, resulting in death of the surrounding tissues.
Hyphema occurs when blood seeps into the anterior chamber as a result of blunt-force trauma or extreme IOP because of unbalanced pressures across the eye — while scuba diving, for example. In addition, required transparency in the chamber can be lost by vascularization, the growth of blood vessels, forming in or near the inner cornea. Though phagocytes, the cells that clean up opaque debris, are available in the chamber, because of transparency requirements, there are too few to clean up either condition, and surgery might be required to restore transparency and sight to the patient.
Corneal tissue lining the anterior chamber can swell up, causing excessive pain because of high-intensity exposure to light, sometimes referred to as snow blindness, when adequate eye protection is not used. As in the natural aging of all polymeric materials or plastics, human tissue surrounding the anterior chamber becomes brittle with age. In that case, any surgery performed on the cornea will have less effect in reshaping the eye for improved vision.