<prompt> True for diurnal variation of intraocular pressure IOP isIOP is usually low in the morning hoursIOP is usually higher in the morning hoursIOP variation is related to plasma acetylcholine levelIn normal eye lOP fluctuation is 10 mm of Hg.  <response>: 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 