Paediatric glaucoma: how should we be treating it?

Here, Peter de Waard, MD discusses his approach to paediatric glaucoma and specifically refers to his experience with the Baerveldt Glaucoma Implant (BGI; AMO). Though, by no means a magic bullet for paediatric glaucoma, he explains the benefits of this procedure and admits that it is not a complication-free treatment approach but complications can be managed, should they arise.

Three years ago, Beck¹ reported significantly greater success rates with aqueous shunt implantation (Ahmed or Baerveldt) compared with trabeculectomy with Mitomycin-C in infants up to 24 months of age. Beck and his team found remarkable differences in success rates between the two procedures, with cumulative probabilities of success at 12 months of 87% for the aqueous shunt group and 36% in the trabeculectomy group.

The mean cumulative probabilities of success in our study of 55 paediatric eyes with a BGI, at 12, 24 and 36 months were 94%, 94% and 85%, respectively. The 12-and 24-month cumulative probabilities of success compare favourably with those reported by investigators who used the Ahmed implants in paediatric patients. They reported success rates ranging from 70% to 93% at 12 months and 58 to 86% at 24 months.

A decline of success rate in our study occurred after 48 (78%) and 60 (44%) months and could be attributed to the limited number of patients with a follow-up of more than four years (15 patients, of which four failed in this follow-up period). Longer follow-up is, therefore, necessary to examine the long-term success rate. However, previous studies suggest that longer follow-up almost always leads to a decrease of surgical success, whether the surgical procedure is glaucoma implant surgery, trabeculectomy, or cycloablation. In our study, no anti-glaucoma medications were needed to control intraocular pressure (IOP) in 64% of our patients at last follow-up.

There may be complications but...

The most frequent complication of BGI in this study was tube related (34%), varying from mild dyscoria to tube exposure. Other studies reported varied complications rates attributable to tube related problems, with figures ranging from 6.5% to 39.1%. The variability in the published incidence of tube related complications after BGI, may be partly attributed to inclusion of differing proportions of buphthalmic eyes in these studies. The thin elastic sclera in buphthalmic eyes gives little support to the implanted tube and predisposes these eyes to changes in size and shape when the IOP is reduced, leading in turn to tube related complications.

In 12 cases (21.8%; all buphthalmic eyes), dyscoria was observed shortly after opening of the tube, which was caused by entrapment of a tuft of peripheral iris tissue in the needle-track (gonioscopy). The entrapment could be a result of a shallow anterior chamber during the period of hypotony after opening of the tube, in combination with movement of the tube in the needle-track creating space next to the tube due to thin elastic sclera. It seems likely that movement of the tube is induced by movement of the eyelids over a hypotonous eye. In combination with the dycoria, we often see an anterior movement of the tube, frequently coming in close contact with the corneal endothelium.