Permanent Ligation of Double-Plate Molteno Implant Distal Tube to Control Late Hypotony

Hypotony is an uncommon complication to develop late after placement of a double-plate Molteno implant. Treatment to date for this has been limited to 2 options: permanent reocclusion of the proximal tube or removal of the tube from the anterior chamber.¹ These methods have the disadvantage of eliminating the entire effect of the implant. The double-plate Molteno implant, however, has the potential advantage of reducing, not eliminating, drainage by stopping drainage to the distal plate. In the following case, we used a new technique, permanent ligation of the distal tube, which allowed treatment of late postoperative hypotony with long-term pressure control and minimal surgical morbidity.

To permanently ligate the distal tube, we incised the conjunctiva and Tenon layer in the space between the distal plate and the overlying rectus muscle. We then bluntly dissected under the muscle and located the tube, taking care to spare the fibrous capsule around the distal plate. Next, we tied a clove-hitch knot around the distal tube with 6-0 a polypropylene suture (Figure 1). The conjunctiva and Tenon layer were sutured with a 9-0 braided polyglactin suture.

We implanted a Molteno double-plate drainage device with adjunctive intraoperative mitomycin C in the left eye of a 17-year-old woman who had a history of congenital ocular rubella syndrome (congenital glaucoma, aphakia, and high hyperopia). A previous trabeculectomy with mitomycin C in that eye had failed. To prevent early postoperative hypotony, we placed a 6-0 polypropylene suture in the proximal tube and ligated the tube with a 6-0 polypropylene suture.¹ After 8 weeks, we removed the intraluminal suture, and her intraocular pressure (IOP) decreased from 28 to 7 mm Hg without medication. For the first 4 months after removing the intraluminal suture, her IOP ranged from 14 to 16 mm Hg and her visual acuity remained at 20/50 OS.

Six months after removing the intraluminal suture, the patient complained of fluctuating, decreased visual acuity. Her visual acuity was 20/200 OS. Her IOP was 7 mm Hg. Fundus examination revealed horizontal macular folds. We diagnosed hypotony with maculopathy and ligated the distal tube of her Molteno implant. In the next several months her visual acuity improved to 20/70 OS, her IOP ranged from 18 to 19 mm Hg with treatment of 1 drop (approximately 20 µL) per day of timolol maleate, and her macular folds substantially decreased.

To halt and reverse the progression of complications associated with hypotony requires elevation of IOP.² Comparison of glaucoma implants in rabbits has shown that the amount of filtration relates to the surface area available for filtration.³ Consistent with this observation, it has been observed that single-plate Molteno implants result in higher IOP and fewer complications related to hypotony than double-plate implants.⁴ Ligation of the distal tube of a double-plate Molteno implant, therefore, raises IOP and treats hypotony because it halves the surface area available for filtration, and yet it still allows filtration through the proximal plate in those situations where some drainage is required.