Inclusion Criteria:  Capable to provide informed consent Diagnosis of optic neuropathy either glaucoma or NAION or optic disc drusen. Only one eye per patient will be selected as the study eye - if both eyes meet the inclusion criteria, the eye with the worse acuity and /or visual field will be selected. The contralateral eye will be left untouched.  Exclusion Criteria:  Pregnant or breastfeeding woman Presence of any ocular pathologies other than glaucoma that contributes to the severe vision loss (retinopathy / maculopathy, severe uveitis, keratopathy, etc.) Diagnosis of glucose intolerance, type 1 or 2 diabetes mellitus Inability to perform reliable visual field Unable to provide informed consent Unable to complete the tests and follow-ups required by the study