What are the most reliable tests to diagnose dry eyes?

Reliability is a key word. Tear volume can be subjectively ascertained by observation with a slit lamp or one can attempt to quantify with a Schirmer's test strip. The quality of the tear and how long it remains stable on the cornea is more critical so we can look at the surface of the cornea for clues to dryness. Low tear volume does not always equate to dry eye and certainly some RS patients complain of dry eye symptoms when the tear volume appears to be adequate. Similarly, punctal occlusion to prevent tear drainage does not always reduce dry eye symptoms.