_In chronic cases_ early iridectomy is desirable, since the root of the iris applied to the posterior surface of the cornea becomes atrophic, so that when an iridectomy is performed the iris tears off at the anterior part of the atrophic portion, leaving the angle of the chamber still occluded by its root (Figs. 112 and 113). It is especially in these cases that a filtrating cicatrix, which sometimes follows iridectomy or sclerotomy, is desirable, and indeed some surgeons (Herbert and Lagrange, see p. 231), have recently performed operations with this idea in view, and it is probable that this operation or cyclo-dialysis will prove to be of use in these cases. Operation is only contra-indicated in a few very rare cases in which the tension is controlled by the use of eserine. (ii) =In congenital glaucoma (bup[h]thalmos).= In this affection the results of iridectomy vary. Without doubt, the tension has been relieved by iridectomy in some cases, and either this operation, sclerectomy, or cyclo-dialysis should be tried if the disease be not too far advanced. (iii) =In secondary glaucoma.= For obvious reasons the predisposing causes should always be taken into consideration. Thus it would be of no use to perform an iridectomy in the case of a growth in the choroid. On the other hand, an iridectomy would be unjustifiable for soft lens matter in the anterior chamber, which merely requires evacuation. An early iridectomy in cyclitis is not likely to influence the course of the disease favourably; at the most a paracentesis is required. As the early stages of cyclitis may give rise to tension, it is essential that every case of glaucoma should be examined for keratitis punctata before operation. [Illustration: FIG. 111. THE ANGLE OF THE ANTERIOR CHAMBER FROM A CASE OF RECENT GLAUCOMA. Showing its occlusion by the base of the iris, A, being adherent to the posterior surface of the cornea, so preventing filtration of the aqueous into the canal of Schlemm, B.] In iris bombé and total posterior synechiæ an iridectomy is indicated more to re-establish the communication between the anterior and posterior chambers than to clear the angle, and therefore it need not be so extensive. In cases of iris bombé where iritis is still present, and in cases of cysts of the iris, transfixion is all that is necessary. It is very doubtful if iridectomy in glaucoma following thrombosis of the central vein is justifiable, for as a rule the tension is not permanently relieved thereby. In secondary glaucoma following cataract extraction or anterior synechiæ, division of the capsule or the anterior synechiæ will often relieve the tension. =Instruments.= Speculum, fixation forceps, Graefe’s knife (with a short, stiff, narrow blade), iris forceps, scissors, and spatula.