Visual apparatus compression can occur from giant AComA aneurysm directed posteriorly and inferiorly 3).
The pattern of visual loss in these cases is variable. The common pattern of visual loss is bilateral field deficits.
The other patterns of visual loss due to AComA aneurysms are central scotoma, bilateral heteronymous deficits, monocular or binocular inferior field loss, asymmetrical bitemporal hemianopsia, and incongruous homonymous hemianopsia 4).
Since internal carotid artery aneurysms and anterior communicating artery aneurysms are located closely to the optic nerve, it is frequently observed during surgery that aneurysm compresses the optic nerve 5) 6) 7).
In most cases, visual symptoms are uncommon in patients, even though intracranial aneurysm may compress the optic pathway. However, in case of large intracranial aneurysm, such visual impairment may be observed due to the pressure from the aneurysm 8) 9) , which are anatomically close to the anterior optic pathway and the arteries from the Circle of Willis (prevalent site of the intracranial aneurysm). Accompanied symptoms include unilateral scotoma or blindness owing to the pressure on the nerve, bitemporal hemianopsia caused by the pressure on the optic chiasm or homonymous hemianopsia due to compression on the optic tract. Such symptoms progress slowly, as with the increasing size of intracranial aneurysm, repeating multiple cycles of improvement and deterioration that are explained by development of a thrombus in the intracranial aneurysm as well as its expansion 10).