This study is evaluating possible non-intraocular pressure (IOP) related effects of the alpha-1 agonist brimonidine in human subjects affected by a progressive glaucomatous optic neuropathy. Brimonidine was proven as neuroprotective in several pre-clinical animal studies.

Patients with open angle glaucoma and a history of relative stability of the visual field are followed for 18 months. A visual field is measured every 3 months for a total number of n = 6 eligible fields at the end of this phase. Then, those eyes showing progression of the field (i.e. deterioration of th eexisting glaucoma), are randomized to receive either 0.2% brimonidine tartrate eyedrops b.i.d. or 360° argon laser trabeculoplasty in one session. Either treatment will be put "on top" of the pre-existing anti-glaucoma therapy. Then, a further 18-month phase is planned, with a sequnece of field taken at the same pace as the previous phase. Progression is detected (and measured) acording to a trend-analysis (i.e. regression vs time of single points and of clusters of adjacent points).

Inclusion Criteria:

• Glaucomatous visual field defect on achromatic perimetry (24/2 Humphrey full threshold,abnormal GHT and CPSD, p<0.01) considered clinically "unstable"
• IOP < 20 mmHg on repeated readings with no more than 2 medications,
• Open angle on gonioscopy,
• Glaucomatous optic neuropathy (HRTII, Moorfields regression analysis),
• Clear lens (LOCS2 score < C1, N0, P0)
• Best corrected visual acuity better than 0.2 LogMAR (ETDRS chart),
• No previous bulbar surgery
• Manifest refraction within - 5 and + 2 diopters
• No comorbidity (AMD and diabetic retinopathy.and negative history for neurological diseases)

Exclusion Criteria:

• Closed angle
• Previous bulbar surgery
• Unstable IOP
• Unreliable visual fields on historic data