Tear histamine levels in vernal conjunctivitis and other ocular inflammations.

Histamine levels were measured in tears from normal volunteers (geometric mean, 5 ng/ml), patients with vernal conjunctivitis (16 ng/ml), and patients with a wide variety of external ocular inflammatory disease (3 ng/ml). Histamine levels were significantly higher in patients with vernal conjunctivitis than in normal subjects (P < 0.01) or patients with other types of ocular inflammation (P < 0.001). We postulate that histamine is an important mediator in the expression of the inflammatory response in vernal conjunctivitis, and that its elevation may be caused by abnormalities in the number of mast cells, the stability of the mast cells or in the system that regulates histamine.