Care must be taken to see that the Tyrrell’s hook presents no sharp angle, and great care is required in its manipulation, otherwise the lens capsule may be damaged, and traumatic cataract will result. If the iris slips from the grasp of the Tyrrell’s hook, iris forceps should be used, the iris being grasped near its free margin and as small a portion as possible withdrawn. =Brudenell Carter’s method.= The ordinary optical iridectomy divides the sphincter iridis and so inhibits the activity of the pupil. With the idea of obviating this, Brudenell Carter removed a small portion of the iris (button-hole), leaving the pupillary margin intact. On the whole the results of the latter operation are no more satisfactory, and the operation is more dangerous to perform owing to the likelihood of wounding the lens, and to the fact that monocular diplopia occasionally results. The pupil should be under the influence of eserine. The incision is made as in the previous operation. De Wecker’s iris scissors are inserted open into the anterior chamber, closed, and the piece of iris which bulges up between the blades cut off; this can usually be withdrawn with the scissors; or if not, it should be removed subsequently by forceps. [Illustration: FIG. 109. OPTICAL IRIDECTOMY. Showing the coloboma.] GLAUCOMA IRIDECTOMY =Surgical and pathological anatomy.= The fluid in the anterior and posterior chambers of the eye is secreted from the ciliary body by a process of modified filtration. The fluid passes partly direct into the posterior chamber and partly behind the suspensory ligament of the lens, making its way forward into the posterior chamber through the fibres of the suspensory ligament. From the posterior chamber it passes into the anterior through the pupil; from the anterior it filters at the angle of the anterior chamber through the ligamentum pectinatum into the canal of Schlemm; thence it is carried into the blood-stream by the venous anastomosis in that region (Fig. 110).