Glaucoma is a progressive optic neuropathy with features similar to nonarteritic anterior ischemic optic neuropathy (NAION), the most common optic neuropathy causing acute vision loss. Glaucoma has an annual incidence rate of 240 per capita, while NAION has an annual incidence of 2.3 per capita among individuals older than 50 years.1,2 Early diabetes mellitus (DM)—defined as an absence of clinically visible diabetic retinopathy—may be associated with upregulation and downregulation of intraocular interferon, interleukins, and other cytokines promoting neuroprotection.3 The initial Ocular Hypertension Treatment Study report documented a protective effect of early DM in glaucoma development, but reanalysis showed no effect.4,5 Studies have shown DM to be a risk factor for NAION, but it is possible that early DM could have neuroprotective effects in NAION. Hayreh and Zimmerman6 had documented less severe visual field loss for diabetic patients with NAION. However, 11% of their participants had juvenile diabetes, 36% had diabetic retinopathy, and the investigators had used manual kinetic perimetry. To discern the role of early DM in NAION, we have studied patients aged 50 years or older without diabetic retinopathy using automated static perimetry.