Long-term Follow-up of Ahmed Glaucoma Valve Tube Position Changes

Abstract

Purpose: To evaluate long-term (4.5 to 6 y) changes in the position of Ahmed glaucoma valve (AGV) tubes. Materials and Methods: Adult patients aged 18 years and above, 1 to 2 months post-AGV implantation were enrolled. Tube position was evaluated using anterior segment optical coherence tomography at baseline and final follow-up. The intracameral tube length (ICL), tube-cornea (TC) distance, and cornea-tube angle were measured. Wilcoxon-signed rank test was used to assess whether the changes in parameters from baseline were significant. Results: In total, 11 eyes of 9 patients were included in the analysis. Mean duration of follow-up was 5.2±0.8 years (4.4 to 6.1 y). The ICL increased from 1.58±0.40 to 1.74±0.62 mm (P=0.18). The TC decreased from 0.36±0.12 to 0.29±0.05 mm (P=0.04). The cornea-tube angle decreased from 27.76±5.57 to 24.82±5.69 degrees (P=0.08). Overall, 73% of the tubes moved toward the cornea (mean 0.11 mm, over 4.4 to 6.1 y). In total, 73% showed an increase in ICL; 45% showed an increase of >0.3 mm [mean 0.50 mm (33%) increase]. Two of 11 tubes (18%) showed no significant change in the parameters (ICL, 0.03 and 0.01 mm increase; TC, 0 and 0.01 mm increase); these tubes were noted to lie on the iris. Conclusions: Tubes tend to move toward the cornea over time. To avoid corneal damage and involvement of the visual axis in the future, tubes should be reasonably short and inserted tangentially, preferably in the posterior one third of the anterior chamber.

Effect of Postoperative Trimming of the Tube Portion of Ahmed Glaucoma Valve on Corneal Endothelial Cell Loss

“…In previous studies, CEC density reduction started at the tube insertion quadrant, and a longer tube length and a reduced cornea-tube angle were suggested as factors associated with CEC loss 3,14. Furthermore, the tube was reported to move toward the cornea, and the intracameral portion of the tube was increased over time 15. It was unclear whether the tube itself touched the corneal endothelium while the patients were lubricating or blinking the eye or the presence of the tube itself in the AC is toxic to CECs.…”

“…3,14 Furthermore, the tube was reported to move toward the cornea, and the intracameral portion of the tube was increased over time. 15 It was unclear whether the tube itself touched the corneal endothelium while the patients were lubricating or blinking the eye or the presence of the tube itself in the AC is toxic to CECs. However, increased CEC loss in the area close to the tube compared with other areas suggests that the shortening of the AGV tube may slow the progression of CEC loss by reducing the possibility of contact with the cornea.…”

Effect of guided Ahmed glaucoma valve implantation on corneal endothelial cells: A 2-year comparative study

“…We examined the iridocorneal contact by slit-lamp examination but did not use gonioscopy. Fifth, the AGV tube may change its position and length over time in the AC; therefore, tube positioning assessment using AS-OCT may vary depending on the time of evaluation [ 31 , 32 ]. In this study, AS-OCT was performed 3–6 months after surgery to access a relatively early tube position.…”

Effect of Guided Ahmed Glaucoma Valve Implantation on Corneal Endothelial Cells: A 2-Year Comparative Study

“…Fourth, the AGV tube may change its position and length over time in the AC; therefore, tube positioning assessment using AS-OCT may vary depending on the time of evaluation. 31,32 In this study, AS-OCT was performed 3-6 months after surgery to access a relatively early tube position. Finally, as the mean time from GDD surgery to corneal decompensation was over 24 months in a previous study, 8 longer follow-up periods would be necessary to further investigate the association with corneal decompensation.…”