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
A patient with ptosis, upper 4 mm of cornea is covered by upper eyelid. Grade of Ptosis is - 
Select and explain. 
A. Mild, B. Moderate, C. Severe, D. Profound
A: Mild
Answer: A: Mild 
Explanation: 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