This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Neuro-ophthalmology, Subject name: Ophthalmology
Typical field defect observed in anterior ischaemic optic neuropathy is 
Select and explain. 
A. Homonymous hemianopia, B. Baring of the blind spot, C. Altitudinal hemianopia, D. Paracentral scotoma
C: Altitudinal hemianopia
Answer: C: Altitudinal hemianopia 
Explanation: ANTERIOR ISCHAEMIC OPTIC NEUROPATHY (AION) It refers to the segmental or generalised infarction of anterior pa of the optic nerve. Etiology: The AION results from occlusion of the sho posterior ciliary aeries. Depending upon the etiology it may be typified as follows: 1. Idiopathic AION: It is the most common entity, thought to result from the atherosclerotic changes in the vessels. 2. Aeritic AION: It is the second common variety. It occurs in association with giant cell aeritis. 3. AION due to miscellaneous causes. Clinical features: Visual loss is usually marked and sudden. Fundus examination during acute stage may reveal segmental or diffuse oedematous, pale or hyperaemic disc, usually associated with splinter haemorrhages. Visual fields show typical altitudinal hemianopia involving the inferior (commonly) or superior half. Ref:- A K KHURANA; pg num:-297