ken vs visual acuity

ken

noun
  • Knowledge, perception, or sight. 

  • Youth or children's group. 

  • A Japanese unit of length equal to six shakus 

  • Range of sight. 

  • The tsurugi 

verb
  • To know, perceive or understand. 

visual acuity

noun
  • The sharpness of vision or sight. 

  • Strength of vision expressed on some definite scale. 

How often have the words ken and visual acuity occurred in a corpus of books? (source: Google Ngram Viewer )