Visual Fields (Chapter 1 of 7)

Visual Fields (Chapter 1 of 7)


NARRATOR: The name “Perkins”
carved in stone. Below a gothic tower,
a boy navigates with a cane. LUISA MAYER:
We do differentiate between visual acuity and visual field, visual acuity being the
centermost part of vision where we focus on things,
we fixate, we see details. Everything else is
the visual field. Even though it’s really one
continuous surface, there really is no separation
in our vision or in our minds between visual acuity
and visual field. Some important things about the
visual field is first of all, as I showed you, if you do this,
you hold your finger when you can’t see it,
you bring it forward. And you see it, you’re aware
of it out in your field, and out here. That’s the fullest extent
of your field. And it’s actually a little
more than 180. It’s actually a little more than
90 degrees from fixation, which is where we really like
to count in this field. NARRATOR: We see a pencil sketch
of an adult male face head-on, with the left eye covered
by the left hand. A shaded, semi-circular
wedge shape depicting the horizontal range
of the right visual field extends from the eye
along a horizontal plane and is bisected by a line,
dividing the wedge into the nasal and temporal
fields. The nasal field is described
by an arc of 60 degrees. The temporal field on the other
side of the axis is 100 degrees for a total range of 160 degrees
in the right eye. MAYER: And then when you’re
thinking about the upper field, the farthest position up you see
is about 60 to 70 degrees. And the farthest position
you could see out, the farthest amount of degrees,
is actually way down here, but I’ll bring it up
so my finger is seen. It’s 80 to 90 degrees,
so it’s very big. NARRATOR: A second sketch shows
an adult male head in profile. A shaded, semi-circular
wedge shape extends from the eye in a vertical plane,
and is bisected by a line representing the
horizontal axis, dividing the wedge into
upper and lower fields. The upper field limit
is 60 degrees from the axis, the lower field 75 degrees, for a total range
of 135 degrees. MAYER: Your vision off to the
side is coarser or rougher, and you don’t see colors
as well, you don’t see details really very well at all. You do see big, gross patterns,
you see contrast differences. So, for example, I can see
the wall contrast over there when I’m just looking
at your face. And that’s really important
for understanding what peripheral vision is for
and what it does. NARRATOR: A third sketch shows
a male figure looking at a chart of concentric circles
that intersect horizontal and vertical axes
at ten degree increments. It is a Goldmann
perimeter chart. A dotted line describes
a rough, oval shape and marks the plotted limits
of the right visual field. The elongated and largest part
of the field is to the right
of the vertical axis. MAYER:
So if we think about what the peripheral field
does do for us, we can think about
when we move around. When we move around through
obstacles, go downstairs, reach for something,
do any physical activity, sports, ride a bicycle. All those things of daily life
that take physical movement, we’re using peripheral vision. It’s really important for that. It’s not that we are not also
using our detail vision, because we are. Because we’re scanning around. We see something to the side,
we scan to it. That’s being cued
by peripheral vision to a target out to the side. So that’s really important. There’s another aspect
of peripheral vision that’s very important, too, and
it’s for doing detailed tasks. For example, for reading,
when you’re reading a page, you fixate on a word,
and you’re anticipating… you’re reading off to the right, and that’s in
your peripheral vision. So you have to be aware
of those word images. You may even see some of them
as you’re scanning to the right. You really need
peripheral vision for fluent reading as well. And it’s one of the problems
with people who have visual field loss,
particularly on the right side. They don’t scan very easily
to the right. And so what they’ll do is
they’ll jump their eye way off, and then scan back,
and then jump way off. Because they don’t see
just to the right of fixation. They don’t see that word
just to the right. NARRATOR:
Fade to black.

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