=Operation.= With the idea of opening up the angle of the anterior chamber by removing the iris as near its root as possible, the incision should be made somewhat further back behind the corneo-sclerotic junction than in cataract extraction. At the same time, if the incision be placed too far back the ciliary body is liable to prolapse into the wound. The old idea of opening up the canal of Schlemm by dividing it has been abandoned, as to do so would certainly result in prolapse of the ciliary body; and even if this did not happen, no good would result, since the canal would become closed subsequently by cicatricial tissue. [Illustration: FIG. 112. THE ANGLE OF THE CHAMBER IN A CASE OF CHRONIC GLAUCOMA. The iris, A, has become atrophic at its root. An iridectomy in this case would not free the angle of the chamber, as the iris would separate at the point A.] Although von Graefe used a keratome for making the incision, most British surgeons of the present day use a Graefe’s knife, as it gives an incision that is less shelving and more irregular, thus predisposing to the formation of a filtrating scar; a good conjunctival flap is obtained with it and there is less risk of wounding the lens. When performing the iridectomy it is practically impossible to cut the iris with scissors at its attachment to the ciliary body, and it is better to rely on tearing it off from the ciliary body, as it is in this situation that the iris is thinnest and most likely to give way, provided it has not become atrophic by prolonged contact with the cornea. In acute cases and in cases of secondary glaucoma where there are many adhesions a general anæsthetic is desirable.