Tear histamine during allergic conjunctivitis challenge.

Tear histamine was measured in 14 patients with allergic conjunctivitis during a challenge test performed at a symptom-free point in time. The allergen challenge caused a rapid increase in the amount of tear histamine in only two-thirds of the patients, but there was a clinical reaction in all. The increase in the tear histamine content occurred in both the challenged and contralateral non-challenged eye, and the increase was also equally high in both. It is probable that the histamine release in the challenged eye takes place in the conjunctiva, whereas in the contralateral eye it is possibly induced by some sympathetic mechanism in the lacrimal gland.