This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Ophthalmology
A woman complains of coloured haloes around lights in the evening, with nausea and vomiting, IOP is normal Diagnosis is – 
Select and explain. 
A. Incipent stage glaucoma open angle, B. Prodromal stage, closed angle glaucoma, C. Migraine, D. Cluster Headache
B: Prodromal stage, closed angle glaucoma
Answer: B: Prodromal stage, closed angle glaucoma 
Explanation: Features of latent PACG (Prodromal stage) are :-


Shallow anterior chamber
Occasionally complain of halos around light
Sometimes slight-haziness or blurring of vision
Normal IOP


It is the only phase of glaucoma, where IOP pressure is normal at all the time. Whereas in incipient stage, there is recurrent elevation of IOP by predisposing factors like dim light.