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
[{'content': 'A patient with ptosis, upper 4 mm of cornea is covered by upper eyelid. Grade of Ptosis is - \nSelect and explain. \nA. Mild, B. Moderate, C. Severe, D. Profound', 'role': 'user'}, {'content': 'Answer: A \nExplanation: It is measured by the amount of cornea covered by the lid and subtracting 2mm. Mild 2mm moderate 3mm severe 4mm Ref :ak khurana 6th edition', 'role': 'assistant'}]