Histamine in human tears.

Tear samples from 13 normal volunteers and nine patients with vernal conjunctivitis were assayed for histamine. Tears in both groups contained histamine. The normal subjects had values ranging from 2.2 to 36 ng/ml with a mean of 10.3 ng/ml. The vernal patients had histamine values ranging from 0 to 125 ng/ml with a mean of 3,.2 ng/ml. The presence of histamine in tears indicates a role for this important mediator in both the physiologic and immunologic processes of the external eye.