Table 1.

 Comparison of the biochemical properties of normal, unstimulated human tears, and serum^51,52

	Tears	Serum
pH	7.4	7.4
Osmolality (SD)	298 (10)	296
EGF (ng/ml)	0.2–3.0	0.5
TGF-β (ng/ml)	2–10	6–33
Vitamin A (mg/ml)	0.02	46
Lysozyme (mg/ml) (SD)	1.4 (0.2)	6
SIgA (μg/ml) (SD)	1190 (904)	2
Fibronectin (μg/ml)	21	205

EGF, epidermal growth factor; TGF-β, transforming growth factor beta; SIgA, surface immunoglobulin A.