The disease developed without any prior warning, with patients complaining of a loss of sensation and numbness in their hands and feet. They became unable to grasp small objects or fasten buttons. They could not run or walk without stumbling, their voices changed in pitch, and many patients complained of difficulties seeing, hearing, and swallowing. In general, these symptoms worsened and were followed by severe convulsions, coma, and eventually death. By October 1956, forty patients had been discovered, fourteen of whom had died: an alarming case fatality rate of 35%. Finding the cause
Researchers from Kumadai also began to focus on the cause of the strange disease. They found that the victims, often members of the same family, were clustered in fishing hamlets along the shore of Minamata Bay. The staple food of victims was invariably fish and shellfish from Minamata Bay. The cats in the local area, which tended to eat scraps from the family table, had died with symptoms similar to those now discovered in humans. This led the researchers to believe that the outbreak was caused by some kind of food poisoning, with contaminated fish and shellfish being the prime suspects. On 4 November, the research group announced its initial findings: "Minamata disease is rather considered to be poisoning by a heavy metal, presumably it enters the human body mainly through fish and shellfish." Identification of mercury
As soon as the investigation identified a heavy metal as the causal substance, the wastewater from the Chisso factory was immediately suspected as the origin.
See also
Adelbert Ames, Jr. (Dartmouth Eye Institute, research in the 1930s and 1940s on aniseikonia)
Anisometropia
Macropsia
Micropsia

References
Further reading
Bannon, Robert E.; Neumueller, Julius; Boeder, Paul; Burian, Hermann M. (June 1970), "Aniseikonia and space perception: After 50 years", American Journal of Optometry & Archives of American Academy of Optometry, 47 (6): 423–441, doi:10.1097/00006324-197006000-00001, PMID 4912937, S2CID 37288776
Bisno, David C. (1994), Eyes in the Storm—President Hopkins Dilemma: The Dartmouth Eye Institute, Norwich, Vermont: Norwich Book Press, p. 288

External links
Aniseikonia Calculator, Chadwick Optical (U.S.A.) — a magnification calculator for iseikonic prescriptions or aniseikonia.