Rose bengal staining test

The purpose of this test is to ascertain indirectly the presence of reduced tear volume through detection of damaged epithelial cells.

The eye is anesthetized topically with proparacaine 0.5%. Tetracaine or cocaine may give false-positive tests because of their softening effect on corneal epithelium.

One drop of 1% rose bengal solution or a drop from a saline-wetted rose bengal strip is instilled in each conjunctival sac. Rose bengal is a vital stain taken up by dead and degenerating cells that have been damaged by the reduced tear volume, particularly in the exposed interpalpebral area. This test is particularly useful in early stages of conjunctivitis sicca and keratoconjunctivitis sicca syndrome.

A positive test will show triangular stipple staining of the nasal and temporal bulbar conjunctiva in the interpalpebral area and possible punctate staining of the cornea, especially in the lower two-thirds.

False-positive staining may occur in conditions such as chronic conjunctivitis, acute chemical conjunctivitis secondary to hair spray use and drugs such as tetracaine and cocaine, exposure keratitis, superficial punctate keratitis secondary to toxic or idiopathic phenomena, and foreign bodies in the conjunctiva.

The stain will also color mucus and epithelial debris, which may mask the results. Certain patients who are normal will show some positive staining to rose bengal on the cornea.

Because of this, conjunctival as well as corneal staining should be present before the diagnosis of keratoconjunctivitis sicca is made. 

See this: http://www.dryeyesummit.org/articles/pros-and-cons-dry-eye-tests