Effect of Prophylactic Aqueous Suppression on Hyperencapsulation of Ahmed Glaucoma Valves

• Intraocular pressure [ Time Frame: 4 months postoperative ] [ Designated as safety issue: No ]
  The primary outcome measure is intraocular pressure (IOP) at 4 months postoperative. This will be a washout IOP (i.e. all glaucoma eye drops will be stopped at 3 months postoperative in all study patients)
  
  

• Hyperencapsulation phase (HEP) [ Time Frame: first 3 months postoperative ] [ Designated as safety issue: No ]

  The HEP endpoint will be met within the first 3 postoperative months if all of the following are met:

  1. IOP increase by 5mmHg or greater compared to previous visit
  2. A bleb appearance in keeping with encapsulation (raised, thickened, firm, dome-shaped)
  3. no other reason for IOP increase
  
  
• Qualified Ahmed Glaucoma Valve success [ Time Frame: 12 months ] [ Designated as safety issue: No ]
  An eye will have qualified success of the Ahmed glaucoma valve if the intraocular pressure (IOP) is at or below 18mmHg at 12 months with use of medications.
  
  
• Absolute Ahmed Glaucoma Valve success [ Time Frame: 13 months ] [ Designated as safety issue: No ]
  An eye will have absolute success of the Ahmed glaucoma valve if the intraocular pressure (IOP) is at or below 18mmHg at 13 months without use of medications. Medications will be stopped at the 12 month visit, and so eyes will be washed out at 13 months.
  
  
• Number of glaucoma medications [ Time Frame: 12 months ] [ Designated as safety issue: No ]
  Will count the number of glaucoma medication classes required to achieve qualified Ahmed Glaucoma Valve success at 12 months.
  
  

Patients with glaucoma requiring tube shunt surgery, with or without simultaneous cataract surgery, will be enrolled in this prospective randomized controlled study at ten sites across Canada and the United States (to be determined). Patients with highly advanced glaucoma at high risk of fixation loss, neovascular glaucoma, chronic uveitis, marked corneal disease, sulfa allergy, renal disease or any contraindication to diamox use will be excluded.

Patients scheduled for Ahmed glaucoma valve surgery, with or without cataract surgery, will be randomized using a stratified central block randomization approach to the treatment group or control group. Those scheduled for combined cataract and tube shunt will be randomized separately from those receiving tube shunt alone. Surgeons will be masked to the postoperative treatment or control group at the time of surgery since randomization will occur when the patient is one-week postoperative Those in the treatment group would receive short-term prophylactic aqueous suppression for the first 3 postoperative months to maintain intraocular pressure (IOP) between 7 and 10mmHg. The control group would not receive prophylactic aqueous suppression, but would be treated using a similar protocol as the treatment group in the event that an Hyperencapsulation phase (HEP) endpoint is met.

Prophylactic aqueous suppression in the study group would only be given for the 1st 3 months postoperatively. At the 3 month visit, aqueous suppression will be stopped. The primary outcome measure is washout IOP at 4 months postoperative. Washout IOP will be checked one month after discontinuation (earlier if needed i.e., advanced glaucoma patients).

Beyond 3 months, aqueous suppressants would be used at the clinician's discretion based on IOP.

At the conclusion of the study, the 4-month postoperative washout IOP, the incidence of HEP, the 12-month IOP, the 13-month washout IOP, and medication requirement would be compared between the treatment and control arms.