Relationship between Tube Parameters and Corneal Endothelial Cell Damage after Ahmed Glaucoma Valve Implantation: A Comparative Study

Purpose: We compared the clinical factors, including anterior chamber tube parameters, in patients with and without corneal endothelial cell damage after Ahmed glaucoma valve (AGV) implantation. Methods: In this retrospective and comparative case series, patients who underwent AGV implantation were enrolled consecutively. Serial specular microscopy was performed before and after AGV implantation. Patients were divided into two groups depending on whether there was a significant decrease in corneal endothelial cell density (ECD), which was determined by each patient's rate of ECD change (%/year), calculated using linear regression analyses. Tube parameters such as the tube-cornea distance (TCD) and tube-cornea angle (TCA) were measured with anterior segment optical coherence tomography. Clinical factors related to the rate of ECD change were evaluated with regression analyses and compared between the two groups. The tipping point at which tube parameters became significantly associated with the rate of ECD change was identified with broken stick regression analyses. Results: There were 30 eyes (32.3%) with ECD damage (group 1) and 63 eyes (67.7%) without damage (group 2). The mean rate of ECD change (%/year) was -18.82 +/- 22.97 and 2.14 +/- 2.93 in groups 1 and 2, respectively (p< 0.001). The TCA was the only clinical factor associated with the rate of ECD change (regression coefficient, beta = 1.254,p< 0.001). The tipping point in the TCA was 26.70 degrees (95% confidence interval, CI: 23.75-29.64 degrees). The mean TCD (mm) was 0.98 +/- 0.38 and 1.26 +/- 0.39 (p= 0.002), and the mean TCA (degrees) was 28.67 +/- 7.79 and 36.35 +/- 5.35 (p< 0.001) in groups 1 and 2, respectively. Conclusions: A wider TCA was protectively associated with the rate of ECD change, and the TCA was significantly narrower in patients with ECD damage. When inserting a tube into the anterior chamber, surgeons should therefore try to secure a wide TCA of about 30 degrees. In patients with a narrow TCA after AGV implantation, increased attention should be directed toward whether ECD decreases continuously.