pair of eyeglasses vs trifocals

pair of eyeglasses

noun
  • A pair of lenses set in a frame worn on the nose and ears in order to correct deficiencies in eyesight or to ornament the face. 

trifocals

noun
  • Spectacles with corrective lenses that have three different powers per eye. 

How often have the words pair of eyeglasses and trifocals occurred in a corpus of books? (source: Google Ngram Viewer )