Reliability of the wetting value of tears.

The wetting value is the length of a Schirmer strip wetted in millimetres for a 5 min test period plus the length of time in seconds for dry spots to appear and has been suggested as a better prognostic test than its components in isolation (Fanti and Holly, 1980). Parameters of these procedures are examined and important shortcomings in the derivation of wetting value discussed. Reliability figures are presented for the Schirmer, tear break-up and wetting value tests. The norms obtained for the tear break-up test are substantially different from those usually assumed and we recommend that practitioners should therefore rely on their own norms rather than published values.