Anterior chamber tube placement of the Ahmed valve linked to endothelial cell loss

Anterior chamber tube placement of the Ahmed valve linked to endothelial cell loss


Glaucoma


Researchers compared corneal endothelium damage after Ahmed glaucoma valve implantation with anterior chamber or ciliary sulcus placement.

Study design

This retrospective, nonrandomized, longitudinal study included 26 pseudophakic eyes with open-angle glaucoma that were medically uncontrolled and undergoing Ahmed valve surgery. Fifteen tubes were placed in the anterior chamber and 11 in the ciliary sulcus. Endothelial cell density (ECD) and average endothelial cell size were measured at 1 and 4 years postoperatively.

Outcomes

One year after the procedure, there were no significant differences between groups in terms of ECD or cell size. At year 4, there was no significant change in ECD or cell size in the ciliary sulcus group; however, there was a significant decline in ECD (P=0.034) and increase in cell size (P=0.007) in the anterior chamber group. Rate of endothelial cell loss was 3.1% per year with anterior chamber tubes and 1.4% per year with sulcus tubes. In both groups, the rate of ECD loss was higher than reported in the general population (0.3–0.6% per year). In the anterior chamber group, ECD and cell size were not tied to the distance between the tube tip to the corneal endothelium.

Limitations

The small sample size limits the power of the study. As a nonrandomized and retrospective study, other ocular factors, such as small pupil, may have influenced the planned location of tube placement. There were more cases of open-angle glaucoma secondary to previous ocular surgery in the anterior chamber group which might have impacted long-term endothelial cell health. Adverse outcomes were not reported.

Clinical significance

When corneal endothelial cell counts are of concern, one might consider a sulcus placement of a tube shunt over anterior chamber placement. However, this study does not address safety differences between the 2 procedures, and may not have found any safety differences due to the small sample size. Although not reported in this study, the rates of hyphema, vitreous hemorrhage and tube incarceration with iris may be higher when tube shunts are placed in the sulcus. Benefits to the corneal endothelium would need to be weighed against risks of alternative tube placement.