Glaucoma tube imaging using anterior segment optical coherence tomography in patients with opaque cornea.

A recent multicenter randomized clinical trial reported on the efficacy and safety of glaucoma drainage device (GDD) implantation.1–3 An obstruction can occur anywhere along a GDD including at the valve mechanism [in Ahmed valves (New World Medical Inc.)]. Postoperatively, direct visualization of the tube orifice to determine tube tip patency is mandatory as part of the functional assessment. In cases where the tube has retracted or is poorly visualized, gonioscopy may allow for tube visualization. However, on occasion especially if the cornea is opaque, tube tip visualization may be impossible. Anterior segment imaging is then required. We describe 3 cases where gonioscopic visualization of the tube was not possible. We used anterior segment optical coherence tomography (Visante AS-OCT; Carl Zeiss Meditech Inc.) to determine tube position and patency. Images of the Ahmed tubes were obtained with the subject in the sitting position. A single investigator (W.K.) used an enhanced high-resolution scan protocol to obtain the tube image after alignment of the scan line parallel to the axis of the drainage tube.