PURPOSE: To understand the pathophysiology of late Ahmed Glaucoma Valve failures and devise strategies to minimize this problem. METHODS: One hundred sixty eyes that had undergone Ahmed Glaucoma Valve implants by one surgeon were retrospectively reviewed. Six eyes with late (greater than 3 months) Ahmed Glaucoma Valve occlusion requiring operative intervention were identified. Two of these eyes underwent initial successful transcameral drainage tube irrigation and four initially required Ahmed Glaucoma Valve exchange. Intraoperative images, postoperative histologic analysis, and Ahmed Glaucoma Valve handling experiments were performed. RESULTS: Two eyes with late occlusion (33%; 1.25% of total implants) were initially successfully treated with irrigation alone. A gap between the valve cover and valve body junction allowed fibrovascular ingrowth and produced valve failure ultimately in five of six eyes (83%; 3.1% of total implants). This gap could be produced by grasping the device along the center line, indenting the valve cover, and damaging the plastic rivets attaching the valve cover to the valve body. Handling the Ahmed Glaucoma Valve outside this 'no touch zone' eliminated this problem. CONCLUSIONS: Leaflet adhesion has a low incidence and may be treated by transcameral drainage tube irrigation. Late onset distal occlusion is best treated by Ahmed Glaucoma Valve exchange with respect for the 'no touch zone.' Respecting the 'no touch zone' over the valve mechanism should avoid creation of gaps between the valve cover and valve body junction, which allow secondary fibrovascular ingrowth. Copyright (C) 2000 Elsevier Science Inc.
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