A small number of patients have lost eyesight in one eye after taking tadalafil. This type of vision loss is called non-arteritic anterior ischemic optic neuropathy (NAION). NAION causes a sudden loss of eyesight because blood flow is blocked to the optic nerve. It is not clear at this time if tadalafil causes NAION. NAION also happens in patients who do not take this medicine. People who have a higher chance for NAION include those who: CIAL1S - From a pharmacy that believes in providing excellent services and the cheapest pr1ces special pri.ces