trokes often affect vision and processing of visual
information. The most common visual deficit is
hemianopia (hem-ee-a-NO-pia) or visual field cut.
Our visual field is the whole area that we
see in front of us — left to right, top to bottom.
Each eye has its own visual field, but the brain combines
the information from both eyes so we only see the world
as one visual field. Like so many processes in the brain,
vision is processed on the opposite side, but it isn’t as
simple as the left eye is handled by the right brain. Instead,
visual stimulation from the left side of each eye is handled
in the right visual cortex. Right-side stimulation of each
eye is processed in the left visual cortex. The visual cortex
is located in the back part of the brain (see How Vision
Works on p. 31). A stroke that injures either the optic nerves
running from the back of the eyeballs through the brain
to the visual cortex or the visual cortex itself will cause
a deficit of vision in the same area of both eyes. Thus, a
stroke in the visual processing area of the right side of the
brain causes a problem with the left visual field of the right
eye and the left visual field of the left eye.
If the blindness involves the same half of the visual field
of each eye, it is called a homonymous hemianopia. There
are variations of field cuts that are much less common.
For example, a field cut may involve less than half, say the
upper left quadrant of both eyes. The top or bottom of the
visual field might be gone or maybe a person can only see
the center of the visual field (the edges are missing); or the
center of the visual field is absent but the edges can be seen.
Further, many of these other types of visual field defects can
be caused by problems other than stroke.
It is not hard to imagine how vision loss would affect
By Jon Caswell
your life. “I think it’s fair to say that vision impacts your
ability to be mobile, to be independent, to read, to drive
and just be productive,” said neuro-ophthalmologist
Adam Cohen, neurology inpatient medical director and
teleneurology director at Massachusetts General Hospital.
“So having vision problems, particularly severe ones like
If you can only see things in the right or left half of the
visual field, why not just move your head to the left or right?
Called ‘scanning,’ this is a basic lesson in the rehabilitation
Half a World Away:
VISUAL FIELD CUTS