This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anatomy, Development and clinical examination, Subject name: Ophthalmology
True for diurnal variation of intraocular pressure (IOP) is 
Select and explain. 
A. IOP is usually low in the morning hours, B. IOP is usually higher in the morning hours, C. IOP variation is related to plasma acetylcholine level, D. In normal eye lOP fluctuation is <10 mm of Hg.
B: IOP is usually higher in the morning hours
Answer: B: IOP is usually higher in the morning hours 
Explanation: Diurnal variation of IOP: Usually, there is a tendency of higher IOP in the morning and lower in the evening. This has been related to diurnal variation in the levels of plasma coisol. Normal eyes have a smaller fluctuation (< 5 mm of Hg) than glaucomatous eyes (> 8 mm of Hg). Reference :- A K KHURANA; pg num:-210