Initial Experience With the New Ahmed Glaucoma Valve Model M4

Short-term Results

Victor Cvintal, MD; Marlene R. Moster, MD; Andrew P. Shyu, BS; Katie McDermott, BS; Feyzahan Ekici, MD; Michael J. Pro, MD; Michael Waisbourd, MD


J Glaucoma. 2016;25(5):e475-e480. 

In This Article


The Glaucoma Research Center of Wills Eye Hospital retrospectively reviewed the charts of glaucoma patients who underwent AGV M4 implantation for uncontrolled IOP on maximum tolerated medications from December 1, 2012 to December 31, 2013. Exclusion criteria included patients younger than 18 years of age and a previous AGV M4 surgery in the same eye. The study protocol was approved by the Institutional Review Board of Wills Eye Hospital and conformed to the principles of the Declaration of Helsinki.

Surgical Technique

All surgeries were performed by 2 experienced surgeons (M.R.M. and M.J.P.) at Wills Eye Hospital using similar techniques in all cases. In the desired quadrant, a fornix-based flap of the conjunctiva and Tenon's capsule was created at the surgical corneal limbus. The AGV M4 was first tested by flushing with balanced salt solution to open the flow restrictor valve. Depending on surgeon preference, viscoelastic material was placed over the base of the plate to facilitate its insertion over the globe. The anterior edge of the plate was then placed 8 mm or more posteriorly to the limbus and fixed to the episclera using 8-0 nylon sutures. During insertion of the plate, the area was irrigated with balanced salt solution to minimize friction from the porous plate. The length of the tube was cut to match the iris border, and a sclerostomy tunnel was made with a 23 G needle. The tube was then inserted into the anterior chamber and fixated to the sclera using 10-0 nylon sutures. A commercially available processed half cornea (VisionGraft Sterile Cornea; Tissue Banks International, Baltimore, MD) or processed double-thickness pericardium (Tutoplast; IOP Ophthalmics, Costa Mesa, CA) was used to cover the tube from the corneoscleral entry to the plate's edge by fixating it to the episclera with 2 interrupted sutures of 10-0 nylon or 8-0 polyglactin (Vicryl; Ethicon Inc., Somerville, NJ). The conjunctiva and Tenon's capsule were then reapproximated to the limbus and fixated with interrupted 10-0 nylon or running 8-0 Vicryl sutures.

Patient Visits

Baseline demographics, glaucoma diagnosis, and previous glaucoma surgeries were collected for each patient preoperatively. The desired quadrant, type of patch graft, and tube position of the surgery were also noted. Follow-up visits were collected at 1 day, 1 week, 1 month, 3 months (±1 mo), 6 months (±2 mo), and 12 months (±3 mo).

Outcome Measures

The primary outcome measure was surgical failure, defined as either (1) IOP<5 mm Hg or >21 mm Hg and/or <20% reduction of IOP from baseline to last follow-up visit, (2) reoperation for glaucoma, and/or (3) loss of light perception. Eyes that did not have a 3-month follow-up or longer were excluded from this outcome measure. All eyes that did not meet the above criteria and were not on supplemental hypotensive drops were defined as complete success. Eyes that did not fail but required additional hypotensive drops were considered qualified success.

Secondary outcome measures included IOP, visual acuity (VA), number of glaucoma medications, early and late complications, reoperations for glaucoma, reoperations for complications, and HP, defined as IOP>21 mm Hg during the first 6 months after a reduction of IOP<22 mm Hg during the first postoperative week.[12–14] Snellen VA was converted to logarithm of the minimum angle of resolution (logMAR) equivalents for analysis. Early complications were noted from day 1 after surgery to 1 month, whereas late complications were recorded after 1 month.[6] Reoperations for glaucoma or complications were defined as additional surgeries requiring another visit to the operating room. Patients who had a reoperation for glaucoma had their subsequent visits censored from analysis.

Statistical Analysis

The differences in IOP and VA at different time periods were assessed for statistical significance using the mixed model to account for the correlation of repeated measurements from the same eye.[25,26] The geometric means of IOP, VA, and their 95% confidence interval (CI) were also calculated. Statistical significance for number of medications was analyzed using the Wilcoxon signed-rank test and the Wilcoxon 2-sample test. A P-value of ≤0.05 was considered statistically significant. Time to failure was compared using Kaplan-Meier curves. Statistical analyses were performed using SAS 9.4 (SAS Institute, Cary, NC) software packages.