How Aqueous humour is produced?
The anterior segment is the front third of the eye that includes the structures in front of the vitreous humour: the cornea, iris, ciliary body, and lens. As blood flows in the cilary body’s capillaries, it is coarsely filtered by the capillaries’ endothelial cells. The resulting plasma is then refiltered by the pigmented and nonpigmented cilary epithelial cells and poured into the posterior chamber of the eye as aqueous humor.
Diamond-Bossert model: Active transport occurring in the nonpigmented cilary epithelial cells induces small osmotic pressure gradients in between the cells. A higher concentration of solutes in the proximal part of the intercellular space generates a flow of water. The concentration diminishes from the proximal part to the distal part, releasing the liquid into the posterior chamber.
Aqueous humour is continually produced by the ciliary processes – to maintain a constant intraocular pressure, the production of aqueous humour must be balanced by an equal rate of aqueous humour drainage. Small variations in the changes in production or outflow of aqueous humour will have a large influence on the intraocular pressure.
The primary route for aqueous humour flow is first through the posterior chamber, then the narrow space between the posterior iris and the anterior lens (contributes to small resistance), through the pupil to enter the anterior chamber. From there, the aqueous humour exits the eye through the trabecular meshwork into Schlemm’s canal, it flows through 25 – 30 collector canals into the episcleral veins. The greatest resistance to aqueous flow is provided by the trabecular meshwork, and this is where most of the aqueous outflow occurs.
The secondary route is the uveoscleral drainage, and is independent of the intraocular pressure, the aqueous flows through here, but to a lesser extent than through the trabecular meshwork.
Glaucoma is a condition characterised by increased intraocular pressure (pressure within the eye) either through increased production or decreased outflow of aqueous humor. Increased resistance to outflow of aqueous humour may occur due to an abnormal trabecular meshwork or to obliteration of the meshwork due to injury or disease of the iris. Uncontrolled glaucoma typically leads to visual field loss and ultimately blindness.