Ophthalmology Phenol red thread test is used for dry eye. This test- 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 💡 Explanation Phenol red thread test is used for dry eye. This test- ✓ Correct Answer: B. Volume of tears isn't measured as it changes color on contact with tears