<prompt> A 52 year old male with a history of hea disease presents with sudden painless loss of vision in one eye. Examination reveals cherry red spot. Diagnosis is:Central retinal vein occlusionCentral retinal aery occlusionDiabetic retinopathyAcute ischemic optic neuritis  <response>: Central retinal aery occlusion: It occurs due to obstruction at the level of lamina cribrosa. Causes sudden painless loss of vision. Retina becomes white due to oedema a cherry red spot is seen at the fovea. Aerioles become narrow blood column within the retinal vessels is segmented. Resuscitation time of the human retina following retinal ischemia is 112 hours. Ref: Review of Ophthalmology by A.K. Khurana, 5th Edition, Page 113 