The patient sees objects much smaller than they are. It can be a type of perceptual syndrome, or illusion, and is often seen as a symptom of ocular vascular disorders or central nervous system disorders. So, what causes small vision? The following are the causes of diminished visual acuity. 1, severe anemia: the blood with oxygen is reduced; blood viscosity increases, such as erythrocytosis, leukemia, etc. due to the slowing of blood circulation, resulting in optic disc hypoxia. 2, systemic vascular disease: hypertension, atherosclerosis, diabetes, migraine, aortitis, carotid artery obstructive lesions. 3.Increased intraocular pressure of glaucoma: the small blood vessels of the optic disc are pressurized, which causes poor blood flow and insufficient blood supply. 4, acute hemorrhage caused by hemorrhagic shock: make the blood pressure too low, so that the small blood vessels on the optic disc is not enough blood supply, blood circulation disorder occurs, thus infarction occurs, local tissue hypoxia. 5, hematological diseases: true erythrocytosis, sickle cell disease, acute hypotension. 6, hypertension, arteriosclerosis, diabetes, temporal arteritis and other vascular diseases: the vessel wall is changed, the vessel is narrowed or occluded, and the small vessels of the optic disc are also changed due to it, causing local ischemia. 7, vasculitis class: giant cell arteritis, nodular polyarteritis, systemic lupus erythematosus, Buergers disease, allergic vasculitis, post-viral vasculitis, after inoculation immunization, syphilis, radiation necrosis.