The Effect of Tube Location on Corneal Endothelial Cells in Patients with Ahmed Glaucoma Valve

Abstract

Purpose: To compare the effects of the Ahmed glaucoma valve (AGV; New World Medical, Rancho Cucamonga, CA) with sulcus versus anterior chamber (AC) tube placement on the corneal endothelial density and morphology over time.

Design: Nonrandomized, interventional study.

Participants: This study included 106 eyes from 101 pseudophakic patients who had the AGV tube placed in the AC (acAGV) and 105 eyes from 94 pseudophakic patients who had the AGV tube placed in the ciliary sulcus (sAGV).

Methods: All patients underwent preoperative specular microscopy, which was repeated postoperatively in 2019. The patients' demographic information, glaucoma diagnoses, and basic ocular information were obtained on chart review. Anterior segment OCT was conducted for patients who underwent sAGV to evaluate the sulcus tube position. Gonioscopy was performed to document peripheral anterior synechiae (PAS). Linear mixed-effects models were used to compare the different ocular and endothelial measurements between the 2 groups and to identify risk factors for endothelial cell density (ECD) loss over time.

Main outcome measures: Monthly change in corneal endothelial measurements, including ECD and coefficient of variation (CV), calculated as the difference between preoperative and postoperative measurements divided by the number of months from the time of surgery to postoperative specular microscopy.

Results: The acAGV and sAGV groups were comparable in all baseline characteristics except that the acAGV group had longer follow-up (37.6 vs. 20.1 months, respectively, P < 0.001). Mean monthly loss in central ECD was significantly more in the acAGV group (mean ± standard deviation: 29.3±29.7 cells/mm²) than in the sAGV group (15.3±20.7 cells/mm², P < 0.0001). Mean monthly change in CV was similar between the 2 groups (P = 0.28). Multivariate analyses revealed that younger age and tube location in the AC were associated with faster central ECD loss (P = 0.02, P < 0.0001, respectively). For patients with sAGV, while PAS was associated with faster central ECD loss (P = 0.002), a more forward tube position tenting the iris was not (P > 0.05).

Conclusions: Compared with anterior segment placement, ciliary sulcus tube implantation may be a preferred surgery approach to reduce endothelial cell loss in pseudophakic patients.

Figure 1.

Scatter-plot of endothelial cell density (ECD) loss over time after Ahmed glaucoma valve (AGV) with tube placement in the anterior chamber (A) versus sulcus (B). The horizontal axis shows the time elapse from AGV surgery to postoperative repeat ECD measurement (months). The vertical axis shows ECD change calculated by subtracting preoperative from postoperative ECD, i.e. postoperative ECD - preoperative ECD (cells/cm²). The line of best fit describes a linear relationship between ECD loss and time interval in both AGV groups, with r describing how well it fits the data.

Figure 2.

Evaluation of tube position and peripheral anterior synechiae (PAS) using anterior segment optical coherence tomography. A. An example of a well positioned sulcus tube. B. An example of sulcus tube pushing the iris forward toward the cornea. C. An example of significant peripheral anterior synechiae in a patient with traumatic glaucoma.