Ahmed Valve Upstream Obstruction Caused by Fibrous Ingrowth: Surgical Approach.

Glaucoma secondary to penetrating keratoplasty can be challenging and multiple surgeries may be needed to control the intraocular pressure (IOP), including the use of glaucoma drainage implants. However, late failure of these drainage implant surgery is common, mostly because of excessive scarring or bleb encapsulation which may require further surgical intervention. We present a case of a young patient referred for advanced glaucoma secondary to penetrating keratoplasty and chronic uveitis. He presented with elevated IOP under maximal therapy, already with 2 failed trabeculectomies and a nonfunctional Ahmed Valve. As no bleb was seen overlying the plate of the valve, an exploratory surgical revision was scheduled. The cause for defective aqueous humour drainage was identified as a fibrovascular ingrowth into the valve's plate slit. We proceeded with removal of this membrane, as well as confirmation of patency with trypan blue and application of mitomycin C to prevent recurrence of the fibrous ingrowth. With a 6 month follow-up, a diffuse bleb exists over the plate, with IOP values within the target values for this patient (<16 mm Hg). This exploratory procedure identified an unusual cause for drainage device failure, as well as reporting its management without explanting the device.