Hemianopsia or hemianopia is visual field loss that respects the vertical midline, and usually affects both eyes, but can involve one eye only. Homonymous hemianopsia, or homonymous hemianopia occurs when there is hemianopic visual field loss on the same side of both eyes. Hemianopias occur because the right half of the brain has visual pathways for the left hemifield of both eyes, and the left half of the brain has visual pathways for the right hemifield of both eyes.
Read more about Homonymous Hemianopsia: Causes, Effects, Vision Restitution Therapy, Help With Mobility, Etymology