Tear lithium concentration: a measurement of dubious clinical value

A mean tear/serum lithium ratio of 0.77 +/- 0.06 was found in 13 volunteers who were given lithium carbonate for 7 days. This finding differs considerably from those of another study, which reported tear and plasma lithium levels to be quite similar. It is suggested that measurement of tear lithium concentration has no clinical utility and that further research along these lines should be discouraged.