A tear osmolarity greater than what value is considered diagnostic for dry eye disease?

• A. > 308 mOsm/L
• B. > 300 mOsm/L
• C. > 320 mOsm/L
• D. > 290 mOsm/L

Answer: (A)

Tear osmolarity is an objective measure of how concentrated the tear film is, and dry eye disease tends to produce a hyperosmolar tear film.

Normal tear osmolarity is around 300 mOsm/L. When the tear film becomes hyperosmolar, the ocular surface experiences stress and inflammation, which are hallmarks of dry eye. A threshold around 308 mOsm/L is used clinically as a diagnostic cutoff because values at or above this level best distinguish dry eye from a normal tear film, offering good specificity. In practice, this means that tear osmolarity above this value supports a dry eye diagnosis, while lower values are less likely to indicate the condition. Keep in mind that larger inter-eye differences can further reinforce the diagnosis if one eye is markedly more hyperosmolar.