Effect of Head Position and Tube Entry on Corneal Endothelial Cells in Patients with Glaucoma Drainage Implants: A Cross-sectional Study Implants: A Cross-sectional Study

Purpose: To investigate the effect of head tilt on the tube position of the Ahmed glaucoma valve (AGV) implanted in patientswith glaucoma and to assess how the head tilt-induced alterations of tube parameters and the level of tube entry influencecorneal endothelial cell density (ECD). Methods: A total of 29 eyes of 26 patients with AGV implantation were included. Tube-cornea distance, tube-cornea angle,and intracameral tube length were measured using anterior segment optical coherence tomography in three different headpositions (neutral, 30° temporalward tilt, and 30° nasalward tilt). The tube entry was assessed using static gonioscopy. ECDwas measured using specular microscopy before and after surgery. Results: The mean tube-cornea distance, tube-cornea angle, and intracameral tube length (neutral: 0.87 ± 0.39 mm, 30.56 ±5.89˚, and 3.10 ± 0.82 mm, respectively) decreased with head tilts (temporalward: 0.82 ± 0.39 mm, 29.27 ± 5.82˚, and 3.04 ±0.82 mm, respectively; nasalward: 0.83 ± 0.40 mm, 29.61 ± 6.04˚, and 3.05 ± 0.81 mm, respectively; all p < 0.01). The multivariateanalyses found age and the tube insertion level to be associated with postoperative changes in the central ECD (p = 0.039and 0.013, respectively), and the postoperative follow-up period and tube insertion level to be associated with the differencebetween the inferonasal and superotemporal ECDs (p = 0.034 and 0.007, respectively). Conclusions: Mild alterations of head positions induced changes in the intracameral tube positions of AGV implants; nevertheless,it did not significantly affect ECD loss. However, the eyes with tubes inserted anteriorly to Schwalbe’s line may bemore susceptible to corneal ECD loss.