Dark haze is a clinical symptom in which the eyes are unable to see and are darkened. Dark haze appears as a transient blackout, which is a sudden, painless visual disturbance that lasts for a few seconds to a few minutes. It is sometimes the first or only symptom of carotid stenosis. Black haze is also seen in postural hypotension, especially for those who are usually weak, in squatting position or lying position, sitting position, if suddenly get up quickly, it is likely to induce postural hypotension, resulting in insufficient cerebral perfusion, then blackness and black haze symptoms can occur. Black haze can also be seen in heart disease patients, such as arrhythmia, cardiac insufficiency, etc., also due to the impact of cerebral perfusion and the emergence of darkness before the eyes, black haze symptoms. It is recommended to consult a doctor in time to clarify the cause of the problem and then treat it.