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.    Fig. 113. Iridectomy for Glaucoma. Failure to relieve the tension owing to the iris not tearing off at its junction with the ciliary body, due to atrophy from prolonged contact with the cornea.

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.

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.

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.

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.