Ophthalmology Phenol red thread test dry eye, true is A Colour change on contact with tears to assess the volume of tears B Uses a pH meter for measurement and interpretation C Measures ocular surface mucin deficiency if thread colour changes to blue D Requires instillation of topical anesthesia before the procedure 💡 Explanation Phenol red thread test dry eye, true is ✓ Correct Answer: A. Colour change on contact with tears to assess the volume of tears