Phenol red thread test is used for dry eye. This test-
*Phenol red dye test measures the production of tears without topical anesthesia, as the dye changes its color to red on contact with tears. It doesn't require pH meter for reading the result. Ref: Ophthalmology Yanoff and Duker 4th/e p.277
Requires topical anaesthetic agent
Volume of tears isn't measured as it changes color on contact with tears
If the color changes to blue, it depicts surface mucin deficiency
Requiras pH meter for reading result
Diseases of orbit, Lids and lacrimal apparatus