Most probable cause of red congested painful eye with mild dilated veically oval pupil is:

Signs of acute primary angle closure glaucoma: Lids appears edematous Conjunctiva is chemosed and congested Cornea becomes oedematous and insensitive Anterior chamber is very shallow Angle of anterior chamber is completely closed as seen on gonioscopy Iris may be discoloured Pupil is semi dilated, veically oval and fixed. It is non-reactive to both light and accommodation. IOP is markedly elevated, usually between 40 and 70 mm of Hg Optic disc is oedematous and hyperemic Fellow eye shows shallow anterior and a narrow angle (latent angle closure glaucoma) Ref: Comprehensive Ophthalmology by A K Khurana, 4th edition, Page 229.