Early detection of progression of glaucoma, and escalating treatment is vital to maintain vision in patients. In this paper from the Early Manifest Glaucoma Trial (EMGT) group they compared the earliest detection of progression in visual fields and monoscopic optic disc photographs at different stages of manifest glaucoma. The study evaluated 306 eyes in 249 patients with manifest open angle glaucoma included in the EMGT. All patients in the trial were followed up regularly by standard automated perimetry and monoscopic optic disc photography, and the median follow-up time was eight years. Progression was assessed in series of optic disc photographs and in series of visual fields using glaucoma change probability maps and the predefined EMGT progression criterion. The proportion of progressions detected first in visual fields and the proportion detected first in optic disc photographs were compared at different stages of glaucoma severity defined by the perimetric mean deviation (MD) of the baseline visual field. The assessment of 210 eyes with early visual field loss, 83 eyes with moderate field loss, and 13 eyes with advanced field loss showed that, among the eyes exhibiting progression, the progression was detected first in the visual field in 80%, 79% and 100%, respectively. In the EMGT material on eyes with manifest open-angle glaucoma, the initial progression was detected much more often in the visual field series than in the optic disc photographs at all stages of disease. This highlights the importance of regular visual fields in addition to disc assessments for glaucoma.