Intraoperative 5-fluorouracil Augmentation of Trabeculectomy

Inclusion Criteria: * A measured intraocular pressure \> or equal to 22 mm Hg on at least one visit before the time of listing for surgery and while on the current drop regime. * The ability to complete a Humphrey 24-2 visual field test with \<20% false positives, \<33% false negatives and \<20% fixation losses, and the presence of 2 locations \> 5decibels (dB) less than normal or one location \>10 dB less than normal. * The presence of a focal or diffuse area of optic disc rim loss, as shown by a reduction of optic rim thickness to less than one tenth of disc diameter at any point on the disc. (alternatively, optic disc which in the opinion of the patient's consultant shows glaucomatous changes as shown by focal or diffuse optic rim thinning) Exclusion Criteria: * Anterior segment neovascularisation * Any intraocular epithelial ingrowth * Retinal or optic nerve neovascularisation * Aphakia * Previous glaucoma filtering surgery * Uveitis * Any previous intraocular surgery * Inability or unwillingness to give informed consent * Inability or unwillingness to return for postoperative follow-up as prescribed in the trial regimen * Unwillingness to accept randomisation * Patient less than 40 years of age * Chemotherapy in the 6 weeks prior to surgery * Any other disease causing visual field loss or likely to cause field loss over the next three years e.g. diabetic retinopathy, pituitary disease or stroke. * Pregnancy or female of childbearing age who may be pregnant at time of treatment. A pregnancy test will be performed on all women of childbearing age to rule out pregnancy. * Cataract that is deemed significant enough to require surgery during the course of the trial or that makes field testing or optic disc recording by either photography or the scanning laser ophthalmoscope unreliable or not technically possible. * Any medical condition likely to prevent the patient from regularly attending for the next three years * Previous conjunctival surgery at proposed site of trabeculectomy * Chronic use of topical or systemic steroids * Previous squint surgery