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Editors Selection IGR 9-2

Glaucoma Drainage Devices: Corneal endothelial cell count after Ahmed GDD

Comment by Steven Gedde on:

24499 Coupling of HRT II and AS-OCT to evaluate corneal endothelial cell loss and in vivo visualization of the Ahmed glaucoma valve implant, Mendrinos E; Dosso A; Sommerhalder J et al., Eye, 2009; 23: 1836-1844

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This study by Mendrinos et al. (1085) assessed corneal endothelial cell loss and tube position following placement of the Ahmed glaucoma valve implant. Ten eyes that underwent Ahmed implantation had measurement of central and peripheral corneal endothelial cell density with confocal microscopy, and imaging of the anterior chamber tube with anterior segment optical coherence tomography (AC-OCT) at six months and one year postoperatively. Mean endothelial cell density decreased by 7.9% ± 2.5 in the central cornea and 7.5% ± 2.4 in the peripheral cornea over a 6 month period. No significant association between central and peripheral endothelial cell loss and tube position (intracameral tube length and distances between the tube and cornea and tube and iris) was observed. The authors conclude that corneal endothelial loss may not be directly related to the drainage tube itself, and other factors may be involved. Corneal endothelial cell loss and corneal edema are known complications of glaucoma drainage device surgery. The mechanism by which an anterior chamber tube causes progressive loss of endothelial cells is not fully understood, but mechanical tubecornea touch and inflammation have been suggested as important factors. The absence of a correlation between tube position and corneal endothelial cell loss in this study does not exclude the importance of mechanical factors. Tube position relative to the cornea can change with eye rubbing and blinking (especially in eyes with low levels of intraocular pressure), and this dynamic relationship would not likely be detected with the AC-OCT measurements made in this study. Other limitations include the small number of patients and lack of preoperative endothelial cell density measurements. This study uses new technology to investigate an important concern about glaucoma drainage devices. The rate of endothelial cell loss was significantly higher than reported age-related endothelial cell loss. Studies like this one are needed to fully evaluate the long-term safety of glaucoma drainage device surgery.

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