This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Diseases of orbit, Lids and lacrimal apparatus, Subject name: Ophthalmology
Phenol red thread test is used for dry eye. This test- 
Select and explain. 
A. Requires topical anaesthetic agent, B. Volume of tears isn't measured as it changes color on contact with tears, C. If the color changes to blue, it depicts surface mucin deficiency, D. Requiras pH meter for reading result
B: Volume of tears isn't measured as it changes color on contact with tears
Answer: B: Volume of tears isn't measured as it changes color on contact with tears 
Explanation: *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