Hemianopia (without an s) and hemianopsia (with an s) are one and the same condition. In Australia and the United Kingdom, web searches are done almost entirely using hemianopia. In the rest of the world, hemianopsia is the preferred spelling. In the interest of catering to the entire world’s internet inquiries, we will be using both spellings interchangeably.
Homonymous hemianopsia is a common vision condition, affecting 1 in 3 stroke patients. It can also be a side effect of certain brain surgeries and abnormalities.
While the normal person has about 180 degrees of field, a patient with homonymous hemianopia has their visual field cut roughly in half.