- The term pseudopia comes from the Greek words pseudos (untruthfulness) and opsis (seeing). It was introduced by the American physician Edward Hammond Clarke (1820-1877) in a book published posthumously in 1878. Clarke used 'pseu-dopia' as an umbrella term for *visual hallucinations, *illusions, and delusions. As he wrote, "The normal process of vision may be appropriately called Orthopia, from op0o ç and ojiroficu: and false perception, or vision, Pseudopia, from ifrev&oç and onroßat." Clarke proposed the following detailed nomenclature of pseudopic phenomena: "According to this nomenclature, false perception, arising from the action of the intracranial visual apparatus, would be called subjective or centric pseudopia; that arising from disturbance of the eye alone, ophthalmic pseu-dopia; and that produced by the presence of external objects, objective or eccentric pseu-dopia. An individual, conscious of the error in his perceptions, would have conscious pseu-dopia; otherwise, unconscious pseudopia." By combining these various terms, Clarke proposed a further distinction into conscious centric pseu-dopia, unconscious centric pseudopia, conscious eccentric pseudopia, etc. Each of these notions was illustrated by him by means of detailed case descriptions. Clarke motivated his proposal for this new nomenclature and classification by asserting that "one advantage ofthese terms over the common ones of hallucination, illusion, and delusion, is that they indicate the precise part of the visual apparatus, whose structural or functional disturbance causes the false perceptions." An additional advantage for Clarke was that these terms had no traditional or preconceived connotations.ReferencesClarke, E.H., Holmes, O.W. (1878). Visions: A study of false sight (pseudopia). Boston, MA: Houghton, Osgood & Company.
Dictionary of Hallucinations. J.D. Blom. 2010.