<prompt> Phenol red thread test is used for dry eye. This test-Requires topical anaesthetic agentVolume of tears isnt measured as it changes color on contact with tearsIf the color changes to blue, it depicts surface mucin deficiencyRequiras pH meter for reading result  <response>: 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 doesnt require pH meter for reading the result. Ref: Ophthalmology Yanoff and Duker 4the p.277 