Ophthalmology Phenol red thread test is used for dry eye: A In the test, volume of tears is measured as it changes color on contact with tears B If the color changes to blue, it depicts surface mucin deficiency C Requires pH meter for reading the result D Requires topical anesthetic agent 💡 Explanation Phenol red thread test is used for dry eye: ✓ Correct Answer: A. In the test, volume of tears is measured as it changes color on contact with tears