Osmolarity comes top

The best way to diagnose and classify dry eye is by measurement of osmolarity, according to a study published in this month's American Journal of Ophthalmology.

The research compared tear osmolarity with tear break-up time, corneal staining, conjunctival staining, Schirmer test and meibomian gland grading. Three hundred and fourteen subjects aged between 18 and 82 years were assessed and the diagnostic scores for each technique were measured against a composite index for dry eye classification.

Of the tests, tears osmolarity was found to have the best diagnostic performance. Using a cut-off value of 312mOsm/l tear hyperosmolarity had a sensitivity of 73 per cent and specificity of 92 per cent. By comparison, corneal staining had poor sensitivity (54 per cent), as had conjunctival staining (60 per cent) and meibomian gland grading (61 per cent). Specificity was poor for tear break-up time (45 per cent) and Schirmer (51 per cent).