semblance vs visual acuity

semblance

noun
  • the way something looks; appearance; form 

  • likeness, similarity; the quality of being similar. 

visual acuity

noun
  • The sharpness of vision or sight. 

  • Strength of vision expressed on some definite scale. 

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