View photos of the edible and medicinal plant Prosopis glandulosa var. torreyana (Western honey mesquite), profiled in Medicinal Plants of the American Southwest and Southern California Food Plants.

A passage from Medicinal Plants of the American Southwest:

The liquid or hardened sap, mixed with water and salt is soothing to conjunctivitis. The solution’s antimicrobial activity will increase if mixed equally with Prickly poppy tea. Even though the sap has some inherent mucilage, over time the tannins can prove drying to the eyes. Therefore it is best to use it for several days at a time, then alternate to Prickly poppy or Desert anemone alone.