**1. Introduction**

Diabetic retinopathy (DR) is a progressive microvascular disease considered as the most important cause of acquired vision loss in the world [1]. World Health Organization (WHO) estimated that in 2030 about 366 millions of adults will be affected with diabetes mellitus (DM) and 191 million with DR [2].

DR is characterized by functional and structural alterations on retinal microcirculation. Ischemia is one of the most important factors for progression of DR. Retinal ischemia is responsible of oxygen defect in retinal tissues because retinal neurons need high levels of oxygen, and this supposes an increased production of pro-angiogenic factor such as vascular endothelial growth factor (VEGF) [3, 4].

Histopathological findings show the existence of structural changes in vascular wall that preceded the visible changes on fundus [5, 6].

On the last decade, optical coherence tomography (OCT) and its recent evolution to the OCT angiography (OCT-A) have drastically improved the diagnosis and follow-up of DR [7].

OCT-A is a technic that allows analysis i*n vivo*, is painless, and separates the different retinal vascular plexus, something impossible with the traditional techniques. Currently, it has recognized four vascular plexus: superficial capillary plexus (SCP),

intermediate capillary plexus(ICP), deep capillary plexus (DCP), and peripapillary radial plexus (PRP) (localized in the peripapilar retinal nervous fiber layer) [8].

The OCT-A shows alterations in these plexus before changes in the fundus will be visible. The earlier stage of DR is defined for the presence of microaneurysm (MA) on the fundus but before that already exist histopathological changes on retinal capillaries. Thus, OCT-A would allow to identify patients affected with DR without fundus changes.
