Ahmed Versus Baerveldt Comparison Study
Condition: Glaucoma
MeSH terms: Glaucoma
Study type: Interventional

Summary: 
      The objective of this study is to compare the long-term safety and efficacy of the Ahmed and
      the Baerveldt implants in patients who are undergoing aqueous shunt implant surgery for
      glaucoma. One eye of eligible patients will be randomized. Outcome measures include
      intraocular pressure, visual acuity, visual field, number of glaucoma medications, glaucoma
      reoperations, and complications, including suprachoroidal hemorrhage, endophthalmitis,
      choroidal effusion, diplopia, corneal edema, and shunt/tube erosion.
    

Detailed description: 
      Background and Significance

      Aqueous shunt devices have traditionally been reserved for treatment of only the most
      refractory glaucomas. However, more recent studies have reported favorable results in
      comparison with trabeculectomy in medically uncontrolled glaucomas at lower risk of
      filtration failure. Consequently, aqueous shunt devices have been used increasingly in
      glaucoma drainage surgery.

      There are two principal designs of implant in common use, the Ahmed glaucoma valve implant
      (New World Medical, Los Ranchos, CA, USA and the Baerveldt implant (Advanced Medical Optics,
      Santa Ana, CA, USA).

      Having both evolved from the Molteno, the Ahmed and Baerveldt devices have in common a tube
      portion that drains aqueous humor from the anterior chamber to a plate that is implanted on
      the equatorial sclera. The size of plate determines the surface area of the drainage bleb.

      The Ahmed and Baerveldt implants differ in two major respects. Firstly, the plate surface
      area of the Baerveldt 350 implant is almost double that of the Ahmed (185 mm2). Secondly, the
      Ahmed has a flow-restrictor that limits early hypotony without the need for additional
      external ligation.

      We propose a randomized prospective clinical trial comparing the long-term safety and
      efficacy of the Ahmed glaucoma valve implant (FP-7) with the 350-mm2 Baerveldt implant
      (101-350) for surgical control of secondary glaucoma and primary glaucoma in eyes that have
      undergone previous ocular surgery.

      Objective

      The objective of this study is to compare the long-term safety and efficacy of the Ahmed FP-7
      implant and the 350-mm2 Baerveldt implant in patients who are undergoing aqueous shunt
      implant surgery. Patients who qualify for the study are randomized to receive either an Ahmed
      FP-7 or Baerveldt BG-101-350 implant. Only one eye of a patient may be enrolled in the study.

      Outcome discrimination between the two treatment groups will be made using typical measures
      of visual function (visual acuity and visual field), intraocular pressure, number of glaucoma
      medications, and glaucoma reoperations. Emphasis will also be placed on complication rates,
      including suprachoroidal hemorrhage, endophthalmitis, choroidal effusion, diplopia, corneal
      edema, and shunt/tube erosion.

      Assignment

      Since the purpose of this study is to compare the safety and efficacy of two surgical
      procedures used in the management of glaucoma, randomization techniques are used to assure an
      unbiased treatment assignment to patients.

      Stratification:

      Patients will be stratified by clinical center. At each Clinical Center, half of the patients
      will receive an Ahmed and half will receive a Baerveldt implant. Randomization takes place at
      the time the patient is enrolled in the study after informed consent is obtained.

      Randomization:

      A permuted variable block randomization scheme stratified by clinical center and type of
      glaucoma will be performed.

      The following scenarios will constitute a failure in the ABC Study for the purposes of
      survival analysis:

        -  IOP > 21mmHG or < 6mmHg on 2 consecutive study visits at visits > 3 months

        -  IOP reduced by < 20% on 2 consecutive study visits at visits > 3 months

        -  Reoperation for glaucoma

        -  Loss of light perception vision

        -  Removal of implant for any reason

      Clinical Procedures

      Visual Acuity

      Visual acuity is an important outcome variable in the ABC Study. Visual acuity is measured
      before pupil dilation, tonometry, gonioscopy, or any other technique that could affect
      vision. Refraction is performed prior to formal measurement of visual acuity by either
      technique at the Qualifying Assessment and at the annual follow-up visits. Snellen visual
      acuity is measured at the Qualifying Assessment and at every follow-up visit.

      Subjective refraction must be performed at the Qualifying Assessment and at the annual
      follow-up visits in order to determine best-corrected visual acuity. It is permissible to use
      a phoropter or trial frame to determine best-corrected Snellen visual acuity.

      Slit Lamp Biomicroscopy Conjunctiva examination Cornea examination An assessment is made of
      the position and length of the tube in the eye. Anterior Chamber examination Iris examination
      Lens examination Tonometry Goldmann applanation tonometry is used to measure the intraocular
      pressure, except when irregular corneal astigmatism, corneal scarring, or corneal edema
      precludes accurate readings. In these cases, the Tono-Pen (Mentor) is used. The intraocular
      pressure is measured prior to pupillary dilation. Whenever possible, the intraocular pressure
      should be checked at the same time of the day as the Qualifying Assessment to minimize the
      effect of diurnal fluctuation The Tono-Pen (Mentor) is used in cases of corneal edema,
      corneal scarring, or irregular corneal astigmatism.

      Central corneal thickness will be measured in each eye, by ultrasound pachymetry. A minimum
      of 5 measurements will be taken and the lowest recorded.

      Motility Evaluation Gonioscopy Ophthalmoscopy Perimetry Visual field assessment is an
      important outcome measure in the ABC Study. Quantitative automated perimetry is performed
      using the Humphrey Field Analyzer. Visual field testing is performed before tonometry,
      gonioscopy, or any other technique that could affect vision. A visual field should be
      attempted in any eye that has sufficient vision to permit finger counting at two feet. Eyes
      with poor central vision may have an intact, off-center island of vision which may be
      measured with perimetry.

      For the ABC Study, a 24-2 threshold test is performed in all patients using a size III white
      stimulus. Visual field testing may be performed with the Swedish Interactive Thresholding
      Algorithm (SITA) or full threshold strategy, but the same testing strategy must be used
      throughout the duration of the study. The pupil diameter should be 3 mm or greater before
      visual field testing is undertaken, and this may require pharmacologic dilation. Standardized
      refraction is performed to determine the patient's distance refraction and best-corrected
      visual acuity prior to visual field testing. The age appropriate plus lens is added to the
      distance refraction. Patient education is provided, and the instrument is set up for the
      test. The technician should monitor the patient during testing. Visual fields are performed
      preoperatively (within one month of enrollment in the study) and annually thereafter. Copies
      of all visual fields are faxed to the Statistical Coordinating Center for evaluation.

      Surgical Procedures

      The type of anesthesia is at the surgeon's discretion.

      Conjunctival Flap:

      An Ahmed FP-7 is used in all cases and implantation is performed in the superotemporal
      quadrant. A limbus-based or fornix-based conjunctival flap may be used depending on the
      surgeon's preference. Sufficient exposure is obtained in the superotemporal quadrant to
      permit placement of the Ahmed plate. A corneal traction suture or episcleral traction suture
      may be used to rotate the globe inferonasally to improve exposure.

      Priming the Implant

      A 28- or 30- gauge cannula is used to prime the Ahmed valve. Occlusion of the tube with a
      ligature is not permitted.

      Attachment of Episcleral Plate:

      The Ahmed plate is sutured to the sclera at a measured distance of 8 - 10 mm posterior to the
      limbus using the two fixation holes on the plate. The type of nonabsorbable suture used is of
      the surgeon's choice.

      Preparation of Tube:

      The tube is trimmed bevel-up to extend 2 to 3 mm into the anterior chamber.

      Insertion of Tube into the Anterior Chamber:

      A 23-gauge needle is used to enter the anterior chamber at the posterior limbus parallel to
      the iris plane. The Ahmed tube is inserted through this entry incision and should be well
      positioned in the anterior chamber away from the corneal endothelium and just above the iris.
      A 23-gauge needle produces an adequate entry incision for the tube without causing aqueous
      leakage around the tube.

      Coverage of Tube:

      A donor patch graft composed of donor sclera, donor cornea, or pericardium is used to cover
      the limbal portion of the tube. The suture selected to fixate the patch graft is of the
      surgeon's choice.

      Conjunctival Closure:

      Tenon's and conjunctiva are reapproximated to the limbus. The suture used for the
      conjunctival closure is determined by the surgeon in keeping with his or her usual practice.

      At the surgeons discretion, a viscoelastic of his or her choice may be inserted into the
      anterior chamber, especially if the anterior chamber shallows after balanced salt solution is
      inserted.

      The use of intraoperative medications is at the surgeon's discretionBaerveldt Implantation
      The type of anesthesia is at the surgeon's discretion.

      Conjunctival Flap:

      A 350-mm2 Baerveldt is used in all cases and implantation is performed in the superotemporal
      quadrant. A limbus-based or fornix-based conjunctival flap may be used depending on the
      surgeon's preference.

      Scleral Exposure:

      Sufficient exposure is obtained in the superotemporal quadrant to permit placement of the
      Baerveldt plate. A corneal traction suture or episcleral traction suture may be used to
      rotate the globe inferonasally and improve exposure.

      Insertion of Episcleral Plate:

      The 350-mm2 Baerveldt plate may be positioned under or over the superior rectus and lateral
      rectus muscles, depending on the surgeon's usual practice. The implant is sutured to the
      sclera at a measured distance of 8 - 10 mm posterior to the limbus using the two fixation
      holes on the plate. The type of nonabsorbable suture used is of the surgeon's choice.

      Occlusion of Tube:

      The Baerveldt tube must be completely occluded in all cases in order to restrict aqueous flow
      to the plate until it becomes encapsulated. This is done to minimize the incidence of
      postoperative hypotony. The method of tube occlusion is left to the discretion of the
      surgeon. Ligation of the tube with a polyglactin suture near the tube-plate junction,
      ligation with a polypropylene suture which is inserted into the anterior chamber with the
      tube, or internal occlusion of the tube using a "rip-cord" technique have all been used
      effectively. A 30-gauge cannula is used to cannulate the end of the tube and confirm complete
      occlusion of the tube. Following tube occlusion, the surgeon may fenestrate the tube if
      desired. The method of tube fenestration is left to the discretion of the surgeon.

      Preparation of Tube:

      The tube is trimmed bevel-up to extend 2 to 3 mm into the anterior chamber.

      Insertion of Tube into the Anterior Chamber:

      A 23-gauge needle is used to enter the anterior chamber at the posterior limbus parallel to
      the iris plane. The Baerveldt tube is inserted through this entry incision and should be well
      positioned in the anterior chamber away from the corneal endothelium and just above the iris.
      A 23-gauge needle produces an adequate entry incision for the tube without causing aqueous
      leakage around the tube.

      Coverage of Tube:

      A donor patch graft composed of donor sclera, dura mater, or pericardium is used to cover the
      limbal portion of the tube. The suture selected to fixate the patch graft is of the surgeon's
      choice.

      Conjunctival Closure:

      Tenon's and conjunctiva are reapproximated to the limbus. The suture used for the
      conjunctival closure is determined by the surgeon in keeping with his or her usual practice.

      The use of intraoperative medications is at the surgeon's discretion.

      Multicenter clinical trials require an organizational structure that provides efficient
      operations and facilitates communication. The following resource centers work together in
      this study:

        -  Clinical Centers (CC)

        -  Statistical Coordinating Center (SCC)

        -  Safety and Data Monitoring Committee (SDMC)

        -  Steering Committee (SC)
    

Intervention name(s): Ahmed implant; Baerveldt implant
Intervention type(s): Device; Device
Intervention description(s): placement of glaucoma drainage device to control intraocular pressure; placement of glaucoma drainage device to control intraocular press
Other intervention name(s): Ahmed fp7; Baerveldt 350
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: glaucoma; Ahmed implant; Baerveldt implant