The lecture provides a detailed description of the development of retinal vessels, vasculogenesis and angiogenesis. The cascade of protective mechanisms of the organism of the system of combating hyperoxia, the system of combating circulatory hypoxia and the key growth factors of the vascular endothelium during angiogenesis are shown. The pathogenesis of retinopathy of prematurity is described and the first phase of ROP development is analyzed in detail, the reasons for the delay in the maturation of vascular autoregulation are explained. The author proposed to distinguish the first preclinical phase in the ROP classification. In contrast to the modern concentration of attention of ophthalmologists on the active and cicatricial stages, the author proposes to pay special attention to the study of the preclinical stage of ROP, where its pathogenesis is formed.