COMPLICATIONS OF GLAUCOMA DRAINAGE DEVICES (GDDs)

 

EARLY COMPLICATIONS

• EXCESSIVE HYPOTONIA
•  Induced by over-drainage of aqueous humor.
• Can lead to anterior chamber (AC) flattening with possible contact between endothelium and the silicone tube, choroidal effusion with detachment, hypotonic maculopathy, or supra-choroidal hemorrhage.
• Valved devices have less frequent early postop hypotonia.

• CHOROIDAL EFFUSION SYNDROME
• Choroidal detachment occurs in 10% to 20% of cases with classic GDDs.
• This can be avoided by implanting the GDD in the eye without inserting the tube in the AC. This allows a connective tissue capsule to develop around the plate in 6-8 weeks. In the second step, the tube is inserted into the AC.
• Alternatively, the tube is blocked by a non-absorbable or absorbable suture.
• However, slits in the silicone tube must be made to achieve some immediate filtration.
• In the case of pars plana implants temporary occlusion of the tube can be done by gas tamponade in the vitreous.

• SUPRA-CHOROIDAL HEMORRHAGE
• Incidence of supra-choroidal hemorrhage after GDD implantation varies from 0 % to 6 %.
• Implants with an IOP-regulation mechanism or a drainage tube ligature have a better prognosis.
• Predisposing factors are hypotony, angle closure glaucoma, and multiple previous surgical events.
• Choroidal hemorrhage represents the greatest risk of reduced vision postoperatively.

• ENDOTHELIUM AND LENS
• Early postop-hypotonia causes shallowing/flattening of AC with a risk of the iris/lens touching the corneal endothelium.
• Consequently, the tube can touch the cornea or iris and get obstructed.

• MOTILITY DISORDERS
• Large implants and a large filtration bleb can affect the motility of the adjacent extraocular muscles.
• Adhesions between the capsule and muscle probably play a role.
• Diplopia can occur.
• In a prospective study, motility disturbances were noticed in 46% of patients after implantation of a double-plate Molteno GDD.
• The study also reported restriction of the superior rectus, Pseudo-Brown syndrome, and paralysis of the superior oblique. However, the diplopia usually regressed within one year.
• With 350-mm² and 500-mm² Baerveldt implants, 7 to 27% of patients had motility disorders, especially with the larger size implants.
• For smaller implants, such as the Ahmed Valve, the incidence is lesser, in the range of 2-3%.

• TRANSIENT HYPERTENSION
• Temporary hypertensive phase can occur in 80% of patients in the first three postop months.
• Occurs from an inflammatory response and fibrovascular scarring surrounding the GDD plate.
• This is a critical phase with the need for inflammatory agents and reduction in IOP since this stage is critical in long-term results.
• GDD implantation can be performed with Mitomycin-C to achieve better long-term results. However, some authors found higher rates of post-op hypotonia with it.

LATE COMPLICATIONS

• ENDOTHELIUM/CATARACT
• Iris, lens or the tube touching the corneal endothelium can cause endothelial loss. Therefore, there is a risk of corneal decompensation.
• Tube implantation through pars plana into the vitreous can be beneficial in post-keratoplasty patients, those with iridial angle anomalies or neovascularization of the iris, and phakic patients with shallow AC.
• Pars plana implantation requires total vitrectomy to prevent vitreous blocking the tube.
• Disadvantages of this method are the risk of retinal complications, the impossibility of visual examination of the tube in case of an apparent obstruction, and a higher risk of hypotonia.
• Induction or progression of cataracts is reported in 8% to 34% of phakic patients. However, the rates are comparable for trabeculectomy and classical glaucoma surgeries.

• EROSION OF THE CONJUNCTIVA
• The conjunctiva at the site of entrance of the tube into the AC, near the limbus is occasionally eroded, causing exposure of the tube.
• The tube should be covered with pericardium, scleral patch, dura, fascia lata, or implanted through a scleral tunnel.
• The risk of exposure of the tube or plate is reported to be between 1%-3%.
• This is a risk factor for endophthalmitis.

• DISLOCATION OF THE TUBE
• In 2-3% of patients tube may displace, causing insufficient filtration.
• Usually occurs from incorrect tube implantation.
• The end of the tube in the AC should be cut diagonally with the bevel facing the endothelium to prevent occlusion by the iris and subsequent displacement.

REFERENCE:

Hille K, Moustafa B, Hille A, Ruprecht KW. Drainage devices in glaucoma surgery. Klin Oczna. 2004;106(4-5):670-81. PMID: 15646493.