Toxic amblyopia, or nutritional optic neuropathy, is a condition where a toxic reaction in the optic nerve results in visual loss. Various poisonous substances may cause the condition as well as nutritional factors.Tobacco amblyopia is a form of toxic amblyopia caused by tobacco containing cyanide. Tobacco amblyopia is marked by a gradual impairment of vision characterised by visual field defects and hindered central vision. Methyl alcohol amblyopia occurs through acute poisoning by methyl alcohol and may lead to complete blindness. Since the term toxic amblyopia is a misnomer according to modern definition of amblyopia, it is now more accurately termed as toxic retinopathies or neuropathies. == References ==
Like other flukes, the liver flukes need intermediate hosts and as a result, the transmission from animals to humans happens in three phases. The first phase is the infection of the snail (the first intermediate host) via feces. They complete their gestation and hatch as cercariae. They leave their snail hosts and infect fish who are their second intermediate host. Lastly, humans ingest the metacercariae in raw and undercooked fish. In humans, the metacercariae complete their life cycle and become full grown liver flukes. Infections
Human infections are most common in Asia, Africa and Latin America. However, trematodes can be found anywhere where untreated human waste is used as fertilizer. Humans can be infected by trematodes either by consuming undercooked contaminated fish or plants, or by ingesting contaminated water. The metacercariae of trematodes attach to fish and plants. In addition, humans can be infected by certain species through swimming in contaminated water. Humans cannot get infected by trematodes directly, trematodes require an intermediate host to do so.Schistosomiasis (also known as bilharzia, bilharziosis or snail fever) is an example of a parasitic disease caused by one of the species of trematodes (platyhelminth infection, or "flukes"), a parasitic worm of the genus Schistosoma. Clonorchis, Opisthorchis, Fasciola and Paragonimus species, the foodborne trematodes, are another. Other diseases are caused by members of the genus Choledocystus. Medically, trematodes are often classed by which organ they invade, which can include blood vessels, the gastrointestinal tract, lungs, or liver.