Acute primary angle glaucoma: It occurs due to a sudden total angle closure leading to severe rise in intraocular pressure (IOP). Typically acute attack is characterized by sudden onset of very severe pain in the eye which radiates along the branches of 5th nerve. Nausea, vomiting and prostrations are frequently associated with pain. Ref: Comprehensive Ophthalmology by A K Khurana, 4th edition, Page 229.