Silicone tubes in glaucoma surgery: the effect of technical modifications on early postoperative intraocular pressures and complications.

One hundred and nineteen eyes with glaucoma were treated by implantation of silicone rubber tubes draining either to encircling inverted gutters (92 eyes) or to integral plates sutured at the equator of the globe. The occurrence of persistent choroidal effusion was related significantly (S less than 0.01) to post-operative hypotony and choroidal haemorrhage appeared to occur during periods of ocular hypotony. This paper describes our surgical modifications to overcome these problems. A one-piece integral tube and plate with a slit-valve mechanism designed to regulate post-operative intraocular pressure had a very variable response in 27 eyes, with mean pressures similar to those after unligated tube and gutters. Ligation of the tube in 34 eyes caused significantly higher mean intraocular pressures on the first two days after surgery than that in 43 eyes without ligation and the incidence of ocular hypotony (less than 7 mmHg) was significantly lower after ligation. However, five eyes with ligated tubes required operative release of the suture because of uncontrollably raised intraocular pressures. Venting of the drainage tube on the anterior chamber side of the occlusive ligation in 15 eyes caused fewer cases of raised post-operative intraocular pressures, but also a moderate increase in the frequency of ocular hypotony. At present a combination of occlusive ligation and a venting stab into the drainage tube in a one-piece tube and plate system appears to be the best design for avoiding short-term ocular hypotony whilst achieving long-term pressure control.