Development of a standardized internet-based system to self-assess skills in optic disc examination for glaucoma risk assessment.Prospective internet-based observational study.Total of 197 participants (glaucoma subspecialists, general ophthalmologists and trainees) from 22 countries.Forty-two optic disc images demonstrating a range of features were selected from 2500 monoscopic disc photographs of normal and glaucomatous eyes. Images were presented to clinicians via website (http://www.gone-project.com). Participants were asked to assess nine topographic features and make a subjective assessment of glaucoma likelihood.Inter-observer agreement using kappa (κ) or weighted kappa (κ(w) ).There was substantial level of inter-observer agreement between glaucoma subspecialists for assessment of glaucoma likelihood (κ(w) = 0.63). Inter-observer agreement was high for haemorrhage (κ= 0.83) and substantial for disc size, disc shape, cup:disc ratio, peripapillary atrophy and cup shape (κ(w) = 0.59-0.68). Subspecialists had stronger inter-observer agreement for glaucoma likelihood and for most disc characteristics than did trainees: the greatest difference being the assessment for retinal nerve fibre layer loss. Analysis of individual disc answers from ophthalmology trainees showed that discs leading to lower agreement of glaucoma likelihood tend to produce lower agreement for the assessment of cup:disc ratio, cup shape, cup depth and retinal nerve fibre layer. Discs with features of moderate to deep cup or cup:disc ratio between 0.6 and 0.8 also lead to lower agreement in glaucoma likelihood.This internet-based system is a readily accessible and standardized tool, for clinicians globally, that permits self-assessment and benchmarking of skills in optic disc examination.