Anatomic Variations of the Iris : In Relation to Basal Iridectomy in the Treatment of Glaucoma

Abstract

Over 100 years ago Albrecht von Graefe described his operation of iridectomy for the treatment of glaucoma. Today, a century later, this same operation with minor modifi­ cations continues to be used in selected cases with marked success. Duke-Elder credits Bowman (1862) with a modification in which part of the iridectomy is performed by tear­ ing a section of iris from its base, where it is inserted into the ciliary body. It is this modi­ fication only, usually referred to as a basal iridectomy, with which this paper is con­ cerned. According to Berens the purpose of this operation of basal iridectomy is to tear the iris at its root and thus reopen the canal of Schlemm and expose the space of Fontana. Stallard states that principle of iridec­ tomy in the treatment of glaucoma is to re­ open the filtration angle. To achieve this the incision must pass through the filtration an­ gle, the iris must be torn away from its root over a fairly wide area, six to eight mm., and no peripheral remnants must be left to oc­ clude the angle. It is likely that the width of the iridectomy (provided that it is not under four mm.) is of less importance than its extension to the root of the It is generally agreed that basal iridectomy is of value in the treatment of narrow angle glaucoma. Briefly, the essential steps in per­ forming the procedure are as follows: The iris is grasped with a smooth iris forceps near its pupillary margin through a section into the anterior chamber placed parallel and a little behind the limbus. One pillar of a sur­ gical coloboma is formed by a cut through the iris with the point of the scissors directed backward toward the root of the iris. Trac­ tion is then applied to the prolapsed iris which is torn free at its root. A second cut with the scissors similar to the first completes the coloboma by creating the opposite pillar and at the same time freeing the section of iris torn by the iridodialysis. Unfortunately basal iridectomy does not always control the glaucoma for which it is performed. This is evidenced in the labora­ tory by the specimens on which this opera­ tion had been performed. This of course is to be expected and the reasons are many and frequently obvious. One of the reasons for failure is thought, often, to be due to faulty technique, in which the iris is not torn at its base but is torn at a point some distance toward the pupil, leav­ ing a stub a millimeter or more long cover­ ing the trabeculae. This forms a broad, firm synechia which closes off the drainage of aqueous and thus aggravates rather than helps the original condition (fig. 1). It is felt, however, that some failures attributed to the faulty technique described may not be due to the technique so much as to normal variations in the structure of the iris. These variations could encourage surgical dialysis