optical illusion vs phantasm

optical illusion

noun
  • An image that is visually deceptive or misleading. 

phantasm

noun
  • Something seen but having no physical reality; a phantom or apparition. 

  • A impression as received by the senses, especially an image, often prior to any interpretation by the intellect. 

How often have the words optical illusion and phantasm occurred in a corpus of books? (source: Google Ngram Viewer )