<prompt> Typical field defect observed in anterior ischaemic optic neuropathy isHomonymous hemianopiaBaring of the blind spotAltitudinal hemianopiaParacentral scotoma  <response>: 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 