However, memantine experience highlights the difficulty in conducting neuroprotection studies 6 Two phase 3 trials (n=2298); primary endpoint - visual field progression over 48 months, with decade - long duration ClinicalTrials.gov identifiers, NCT00141882 and NCT00168350; Ophthalmology. 2018 Dec;125(12):1874 - 1885. Key challenges: • Slow and prolonged disease course • Variable progression rates among patients • High variability in visual field measurements • Need to test neuroprotective agent on top of standard of care (IOP lowering eyedrops)