Blindness is often caused by ophthalmic diseases, neurological diseases, systemic diseases, poisoning, side effects of medications, trauma and other factors, of which ophthalmic disease factors are the most common. Patients may experience changes in vision slowly or suddenly, such as blurred vision, diplopia and rapid loss of vision, with or without accompanying precursors such as eye pain, headache, nausea and vomiting, red eyes and tearing.