Physiology of Aqueous Humor Formation, Diurnal Fluctuation of Intraocular Pressure and its Significance for Glaucoma

In the human eye there is a balance between production of aqueous humor as well as its drainage. The intraocular pressure is held through different mechanisms in a stable balance. The aqueous humor is secreted by the ciliary epithelium lining the ciliary processes. Three physiological processes contribute to the formation and chemical composition of the aqueous humor: diffusion (5%), ultrafiltration (15%) and active secretion (80%). The normal intraocular pressure amounts to 15 +/- 3 mmHg, the normal diurnal fluctuation 5 mmHg. Aqueous humor leaves the eye by passive bulk flow via two pathways: the trabecular route and the uveoscleral route. In glaucoma patients this balance is disturbed resulting in individual high intraocular pressure or, respectively, high diurnal fluctuations. This leads to loss of retinal ganglion cells and visual field loss. As a recommendation for glaucoma patients it is useful to construct diurnal intraocular pressure curves to evaluate the "type of pressure" and to determine the diurnal fluctuations or, respectively, the time of the pressure maxima. With this knowledge, treatment of glaucoma patients can be managed in a more individualised manner and it seems to slow down the progress of the disease better than by merely reducing the intraocular pressure.