Otago Glaucoma Surgery Outcome Study. Atypical late failure of drainage following clear cornea trabeculectomy.

Background: Bleb scarring is the major cause of late drainage failure following the standard trabeculectomy. To overcome this, Cairns described a modification of his original technique, which he termed the clear cornea trabeculectomy. The essential feature was communication between the anterior chamber and subconjunctival space without intraoperative disturbance of the conjunctival or Tenon's tissue. As there is little published data on Cairns' clear cornea trabeculectomy, this study aimed to assess the long-term success of this procedure relative to conventional trabeculectomy.

Methods: Patients who underwent clear cornea trabeculectomy at Dunedin Hospital were identified. Cases in which late failure occurred were subject to a detailed review. Records of all patients in whom late failure of drainage occurred following conventional trabeculectomy performed since 1985 were also reviewed. The nature of late drainage failure associated with these different procedures was assessed.

Results: Late failure of drainage occurred in three of 21 eyes following clear cornea trabeculectomy. In each case there was an accelerated drainage failure with a dramatic rise in intraocular pressure. Consequent visual loss occurred in two patients. Late failure occurred in 32 of the 450 cases of conventional trabeculectomy, in all of which the pressure rise was gradual and less acute.

Conclusions: This report highlights a previously unreported type of late failure associated with clear cornea trabeculectomy, which may result in significant visual loss. This reinforces the view that the standard Cairns' trabeculectomy is a safer procedure.