Trabeculectomy with fistula formation in the African.

Abstract

Operations on the trabecular meshwork in order to reduce raised intraocular pressure are receiving increasing prominence. Redmond Smith (i960) opened the trabecular tissue by passing a nylon thread along the canal of Schlemm via an ab externo incision, and by a further incision and by picking up the distal end of the thread, he ruptured the trabecular meshwork by pulling on the thread like a bow. Allen and Burian (I962) passed an instrument into the canal of Schlemm via an ab externo incision and ruptured the trabecular tissue. Strachan (I967) and Harms and Dannheim (I969) have modified this further until now the operation of trabeculotomy "ab externo" has been well documented. Krasnov (i968) described the operation of sinusotomy or externalization of the canal of Schlemm in cases in which the obstruction to outflow may be intrascleral, and Walker and Kanagasundaram (i964) have also followed this principle. Trabeculectomy or removal of trabecular meshwork through an ab externo incisioni (Cairns, I968) allows the aqueous to flow through the now exposed cut ends of Schlemm's canal and then to leave the eye via the normal exit channels. In African patients, in whom the problems of failure of drainage operations have been shown to be due mainly to fibrosis derived from the sclera and from Tenon's capsule (Welsh, I970), it was thought that trabecular operations would be theoretically advantageous. Trabeculectomy was chosen as the operation of choice because of the results obtained by others up to this time, and also because histological examination of the trabecular tissue could then be performed and so afford direct evidence of any obstructive pathology. Trabeculectomy as described by Cairns (i 968) was therefore performed in a series of cases. It was found that trabeculectomy in itself reduced the intraocular pressure only partially. A controlled series of cases in which the trabeculec- tomy was combined with intentional fistula formation was also carried out, and these cases showed a much higher success rate than those in which trabeculectomy was used alone. This combined procedure seems also to be more successful than the standard drainage procedures, and the purpose of this paper is to discuss these findings and to suggest that in the more heavily pigmented races the combined procedure has considerable merit.