The human eye can be compared to a photographic camera. Visual information passes first through a transparent window, the cornea, and afterwards the pupil in the centre of the iris. The iris, the coloured part of the eye, plays the role of a diaphragm that regulates the amount of light that enters the eye. The lens in the eye focuses the image onto the retina. The retina is like the film of a camera or the chip in a digital camera and sends the image into the optic nerve. The central part of the retina, which is the area of sharp vision, is called macula. The optic nerve is like a cable, which transmits all visual information to the brain. This cable includes about 1,200,000 neural visual fibres. In chronic glaucoma there is a progressive loss of the visual fibres.
The intraocular pressure
Inside the eyeball there is a certain level of pressure, the intraocular pressure, which is regulated by a continuous exchange of a fluid, the aqueous humour. The intraocular pressure is essentially unrelated to arterial blood pressure. Aqueous humour is continuously secreted into the eye by a tissue called the ciliary body. Aqueous humour continuously leaves the eye at the intersection between the cornea and the iris at the level via a special tissue called the trabeculum or trabecular meshwork. The producion of the aqueous humour by the ciliary body and its flow and drainage is an active, continuous phenomenon, essential for the health of the eye.