**3.5 Ocular surface disease index (OSDI)**

OSDI (Allergan, Inc., Irvine, CA) is a frequently used instrument to assess DE and provides a quantifiable assessment of DE symptom frequency and the impact of these symptoms on vision-related functioning. It contains 12 items, and the score can range from 0 (no symptoms) to 100 (severe symptoms) points; 0 to 12 represents normal, 13 to 22 represents mild DED, 23 to 32 represents moderate DED, and greater than 33 represents severe DED.
