Over the last 20 years, the number of people suffering from diabetes or prediabetes has doubled. Retinal microvascular changes (i.e. microaneurysms and haemorrhages) and neurodegenerative changes (i.e. degeneration of ganglion cells and axons) are a result of diabetes. These changes can cause vision loss, impaired dark adaptation and colour blindness. Due to diabetes, neurodegenerative changes of the corneal subbasal nerve plexus may occur as well, including reduced nerve fibre length. Therefore, diabetes is associated with delayed corneal epithelial healing, impaired corneal sensitivity and corneal erosions. This dissertation shows that neurodegenerative changes may also occur in the absence of microvascular changes. Approximately 50 percent of neuronal damage of retina, optic nerve and cornea is already present in prediabetes. Early diagnosis of and regular follow-up appointments with people with prediabetes can have a major impact on public health and public health costs.