This is an important disease in which the ciliary body and iris seem specially concerned. It consists in an increase of the pressure of the fluids inside the eyeball, with consequent injury to the structures of the eye.

The secretion and absorption of the intraocular fluids have been made the subject of much study and experiment. As the withdrawal of the aqueous humour is quickly followed by its replacement, then-seems no doubt that an active secretion goes on in the eye. It is generally agreed that the ciliary body is the chief agent in supplying both the vitreous and aqueous humours, the latter passing through the pupil to the anterior chamber. The principal absorption of fluid is probably at the periphery of the anterior chamber, at the angle formed by the iris behind and the cornea and anterior part of the sclerotic in front. This space is called variously the sinus of the anterior chamber and the filtration angle. This sinus is in communication by means of spaces in the ligamentum pectinatum with Schlemm's canal, which is a channel running round the eye near the boundary between the sclerotic and the cornea. This canal again communicates with the veins of the anterior part of the sclerotic. The retention of this filtration angle or sinus is thus necessary to the absorption of the aqueous humour. Increase of the intraocular pressure may be produced by excessive secretion of fluid, or by defective absorption, but it is mainly by the latter that it is brought about)

Glaucoma results chiefly from interl'eieme with the sinus men tioned above. Such interference takes place when, by reason of oak meat of the ciliary body, the base of the iris is pushed forward and so fills up this angle. In most cases the iris is pushed forward so as bo be in contact with the cornea, and in many it is actually adherent so as to abolish the sinus. The cause of this displacement has been variously stated, and is not well understood. According to Priestley Smith there is usually, as a predisposing cause, smallness of the globe, and a consequent forward displacement of the lens carrying the iris with it. The sinus being already curtailed, an inflammation or merely a congestion of the ciliary body may push forward the iris so as to close the angle. Besides these cases of more obscure origin, which are included under the designation of Primary glaucoma, the intraocular pressure is increased in some other diseases, of which the chief are tumours. These may act directly by increasing the contents of the globe, but they are also found to produce the glaucoma by pressure on the sinus.

The effects of the increased pressure are seen chiefly in the retina and optic nerve. The optic nerve entrance is less resistant than the sclerotic, being formed by the lamina cribrosa, which gives passage to the fibres of the nerve. This structure yields, and is hollowed out so that a depression is produced in the fundus of the eye. Atrophy of the nerve fibres is a necessary consequence with advancing blindness. The cornea is also rendered dull and obscure and non-sensitive.