- Diagnosis and classification: all patients should have the symptoms and signs of severe dry eye (conforming to grade 3 or 4 in DEWS2007). Should have at least two positive symptoms such as dryness, foreign body sensation, burning, asthenopia, red eye or secretion. Tear film breakup time (TFBUT) shorter than 5 seconds and/or Schirmer I less than 5 mm/5 min. Corneal fluorescein staining more than 6 scores and (or) more than 3 scores of bulbar conjunctiva lissamine green liquor.