This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Errors of Refraction, Subject name: Ophthalmology
[{'content': 'Phenol red thread test dry eye, true is \nSelect and explain. \nA. 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', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. (a) Colour change on contact with tears to assess the volume of tearsRef: Yanoff 4/e, p. 277Phenol red thread test was developed by Hamano et al to obviate the disadvantages of Schirmer's test by eliminating the need for anesthesia.3 mm. of fine dye-impregnated 75mm cotton thread is placed in the lateral one-fifth of the inferior palpebral lid margin for 15 seconds, alkalinity changes its color bright orange to red from tear contact.", 'role': 'assistant'}]