<s>
In	O
biology	O
,	O
binocular	B-Algorithm
vision	I-Algorithm
is	O
a	O
type	O
of	O
vision	O
in	O
which	O
an	O
animal	O
has	O
two	O
eyes	O
capable	O
of	O
facing	O
the	O
same	O
direction	O
to	O
perceive	O
a	O
single	O
three-dimensional	B-Algorithm
image	I-Algorithm
of	O
its	O
surroundings	O
.	O
</s>
<s>
Binocular	B-Algorithm
vision	I-Algorithm
does	O
not	O
typically	O
refer	O
to	O
vision	O
where	O
an	O
animal	O
has	O
eyes	O
on	O
opposite	O
sides	O
of	O
its	O
head	O
and	O
shares	O
no	O
field	O
of	O
view	O
between	O
them	O
,	O
like	O
in	O
some	O
animals	O
.	O
</s>
<s>
It	O
can	O
give	O
stereopsis	B-Algorithm
in	O
which	O
binocular	O
disparity	O
(	O
or	O
parallax	B-Device
)	O
provided	O
by	O
the	O
two	O
eyes	O
 '	O
different	O
positions	O
on	O
the	O
head	O
gives	O
precise	O
depth	O
perception	O
.	O
</s>
<s>
It	O
allows	O
the	O
angles	O
of	O
the	O
eyes	O
 '	O
lines	O
of	O
sight	O
,	O
relative	O
to	O
each	O
other	O
(	O
vergence	B-Algorithm
)	O
,	O
and	O
those	O
lines	O
relative	O
to	O
a	O
particular	O
object	O
(	O
gaze	O
angle	O
)	O
to	O
be	O
determined	O
from	O
the	O
images	O
in	O
the	O
two	O
eyes	O
.	O
</s>
<s>
This	O
advantage	O
was	O
pointed	O
out	O
by	O
Leonardo	B-Application
da	I-Application
Vinci	I-Application
,	O
who	O
noted	O
that	O
a	O
vertical	O
column	O
closer	O
to	O
the	O
eyes	O
than	O
an	O
object	O
at	O
which	O
a	O
creature	O
is	O
looking	O
might	O
block	O
some	O
of	O
the	O
object	O
from	O
the	O
left	O
eye	O
but	O
that	O
part	O
of	O
the	O
object	O
might	O
be	O
visible	O
to	O
the	O
right	O
eye	O
.	O
</s>
<s>
Other	O
phenomena	O
of	O
binocular	B-Algorithm
vision	I-Algorithm
include	O
utrocular	B-Algorithm
discrimination	I-Algorithm
(	O
the	O
ability	O
to	O
tell	O
which	O
of	O
two	O
eyes	O
has	O
been	O
stimulated	O
by	O
light	O
)	O
,	O
eye	O
dominance	O
(	O
the	O
habit	O
of	O
using	O
one	O
eye	O
when	O
aiming	O
something	O
,	O
even	O
if	O
both	O
eyes	O
are	O
open	O
)	O
,	O
allelotropia	O
(	O
the	O
averaging	O
of	O
the	O
visual	O
direction	O
of	O
objects	O
viewed	O
by	O
each	O
eye	O
when	O
both	O
eyes	O
are	O
open	O
)	O
,	O
binocular	B-Algorithm
fusion	I-Algorithm
or	O
singleness	O
of	O
vision	O
(	O
seeing	O
one	O
object	O
with	O
both	O
eyes	O
despite	O
each	O
eye	O
having	O
its	O
own	O
image	O
of	O
the	O
object	O
)	O
,	O
and	O
binocular	O
rivalry	O
(	O
seeing	O
one	O
eye	O
's	O
image	O
alternating	O
randomly	O
with	O
the	O
other	O
when	O
each	O
eye	O
views	O
images	O
that	O
are	O
so	O
different	O
they	O
cannot	O
be	O
fused	O
)	O
.	O
</s>
<s>
Binocular	B-Algorithm
vision	I-Algorithm
helps	O
with	O
performance	O
skills	O
such	O
as	O
catching	O
,	O
grasping	O
,	O
and	O
locomotion	O
.	O
</s>
<s>
Optometrists	O
and	O
orthoptists	O
are	O
eyecare	O
professionals	O
who	O
fix	O
binocular	B-Algorithm
vision	I-Algorithm
problems	O
.	O
</s>
<s>
Some	O
animalsusually	O
,	O
but	O
not	O
always	O
,	O
prey	B-Application
animalshave	O
their	O
two	O
eyes	O
positioned	O
on	O
opposite	O
sides	O
of	O
their	O
heads	O
to	O
give	O
the	O
widest	O
possible	O
field	O
of	O
view	O
.	O
</s>
<s>
Examples	O
include	O
rabbits	B-Algorithm
,	O
buffalo	O
,	O
and	O
antelopes	O
.	O
</s>
<s>
Some	O
other	O
animalsusually	O
,	O
but	O
not	O
always	O
,	O
predatory	O
animalshave	O
their	O
two	O
eyes	O
positioned	O
on	O
the	O
front	O
of	O
their	O
heads	O
,	O
thereby	O
allowing	O
for	O
binocular	B-Algorithm
vision	I-Algorithm
and	O
reducing	O
their	O
field	O
of	O
view	O
in	O
favor	O
of	O
stereopsis	B-Algorithm
.	O
</s>
<s>
However	O
,	O
front-facing	O
eyes	O
are	O
a	O
highly	O
evolved	O
trait	O
in	O
vertebrates	O
,	O
and	O
there	O
are	O
only	O
three	O
extant	O
groups	O
of	O
vertebrates	O
with	O
truly	O
forward-facing	O
eyes	O
:	O
primates	O
,	O
carnivorous	O
mammals	O
,	O
and	O
birds	B-Application
of	I-Application
prey	I-Application
.	O
</s>
<s>
These	O
are	O
usually	O
animals	O
that	O
need	O
fine	O
depth	O
discrimination/perception	O
;	O
for	O
instance	O
,	O
binocular	B-Algorithm
vision	I-Algorithm
improves	O
the	O
ability	O
to	O
pick	O
a	O
chosen	O
fruit	O
or	O
to	O
find	O
and	O
grasp	O
a	O
particular	O
branch	O
.	O
</s>
<s>
The	O
angle	O
between	O
the	O
line	O
of	O
sight	O
of	O
the	O
two	O
eyes	O
when	O
fixating	O
a	O
point	O
is	O
called	O
the	O
absolute	O
disparity	O
,	O
binocular	O
parallax	B-Device
,	O
or	O
vergence	B-Algorithm
demand	O
(	O
usually	O
just	O
vergence	B-Algorithm
)	O
.	O
</s>
<s>
The	O
relation	O
between	O
the	O
position	O
of	O
the	O
two	O
eyes	O
,	O
version	O
and	O
vergence	B-Algorithm
is	O
described	O
by	O
Hering	O
's	O
law	O
of	O
visual	O
direction	O
.	O
</s>
<s>
Or	O
they	O
are	O
disjunctive	O
(	O
in	O
opposite	O
direction	O
)	O
,	O
vergence	B-Algorithm
eye	I-Algorithm
movements	O
.	O
</s>
<s>
The	O
relation	O
between	O
version	O
and	O
vergence	B-Algorithm
eye	I-Algorithm
movements	O
in	O
humans	O
(	O
and	O
most	O
animals	O
)	O
is	O
described	O
by	O
Hering	O
's	O
law	O
of	O
equal	O
innervation	O
.	O
</s>
<s>
A	O
starling	B-Application
,	O
for	O
example	O
,	O
has	O
laterally	O
placed	O
eyes	O
to	O
cover	O
a	O
wide	O
field	O
of	O
view	O
,	O
but	O
can	O
also	O
move	O
them	O
together	O
to	O
point	O
to	O
the	O
front	O
so	O
their	O
fields	O
overlap	O
giving	O
stereopsis	B-Algorithm
.	O
</s>
<s>
A	O
remarkable	O
example	O
is	O
the	O
chameleon	B-Device
,	O
whose	O
eyes	O
appear	O
as	O
if	O
mounted	O
on	O
turrets	O
,	O
each	O
moving	O
independently	O
of	O
the	O
other	O
,	O
up	O
or	O
down	O
,	O
left	O
or	O
right	O
.	O
</s>
<s>
Nevertheless	O
,	O
the	O
chameleon	B-Device
can	O
bring	O
both	O
of	O
its	O
eyes	O
to	O
bear	O
on	O
a	O
single	O
object	O
when	O
it	O
is	O
hunting	O
,	O
showing	O
vergence	B-Algorithm
and	O
stereopsis	B-Algorithm
.	O
</s>
<s>
Accommodation	O
and	O
vergence	B-Algorithm
.	O
</s>
<s>
Fusion	O
of	O
images	O
(	O
commonly	O
referred	O
to	O
as	O
'	O
binocular	B-Algorithm
fusion	I-Algorithm
 '	O
)	O
occurs	O
only	O
in	O
a	O
small	O
volume	O
of	O
visual	O
space	O
around	O
where	O
the	O
eyes	O
are	O
fixating	O
.	O
</s>
<s>
As	O
a	O
result	O
of	O
this	O
overlap	O
of	O
vision	B-Algorithm
,	I-Algorithm
binocular	I-Algorithm
vision	O
provides	O
depth	O
.	O
</s>
<s>
Stereopsis	B-Algorithm
(	O
from	O
stereo	O
-	O
meaning	O
"	O
solid	O
"	O
or	O
"	O
three-dimensional	O
"	O
,	O
and	O
opsis	O
meaning	O
“	O
appearance	O
”	O
or	O
“	O
sight	O
”	O
)	O
is	O
the	O
impression	O
of	O
depth	O
that	O
is	O
perceived	O
when	O
a	O
scene	O
is	O
viewed	O
with	O
both	O
eyes	O
by	O
someone	O
with	O
normal	O
binocular	B-Algorithm
vision	I-Algorithm
.	O
</s>
<s>
There	O
are	O
two	O
aspects	O
of	O
stereopsis	B-Algorithm
:	O
the	O
nature	O
of	O
the	O
stimulus	O
information	O
specifying	O
stereopsis	B-Algorithm
,	O
and	O
the	O
nature	O
of	O
the	O
brain	O
processes	O
responsible	O
for	O
registering	O
that	O
information	O
.	O
</s>
<s>
Retinal	B-Algorithm
disparity	I-Algorithm
is	O
the	O
separation	O
between	O
objects	O
as	O
seen	O
by	O
the	O
left	O
eye	O
and	O
the	O
right	O
eye	O
and	O
helps	O
to	O
provide	O
depth	O
perception	O
.	O
</s>
<s>
Retinal	B-Algorithm
disparity	I-Algorithm
provides	O
relative	O
depth	O
between	O
two	O
objects	O
,	O
but	O
not	O
exact	O
or	O
absolute	O
depth	O
.	O
</s>
<s>
The	O
closer	O
objects	O
are	O
to	O
each	O
other	O
,	O
the	O
retinal	B-Algorithm
disparity	I-Algorithm
will	O
be	O
small	O
.	O
</s>
<s>
If	O
the	O
objects	O
are	O
farther	O
away	O
from	O
each	O
other	O
,	O
then	O
the	O
retinal	B-Algorithm
disparity	I-Algorithm
will	O
be	O
larger	O
.	O
</s>
<s>
To	O
maintain	O
stereopsis	B-Algorithm
and	O
singleness	O
of	O
vision	O
,	O
the	O
eyes	O
need	O
to	O
be	O
pointed	O
accurately	O
.	O
</s>
<s>
Move	O
the	O
finger	O
around	O
;	O
this	O
is	O
to	O
break	O
the	O
reflex	O
that	O
normally	O
holds	O
a	O
covered	O
eye	O
in	O
the	O
correct	O
vergence	B-Algorithm
position	O
.	O
</s>
<s>
The	O
cover-uncover	O
test	O
can	O
also	O
be	O
used	O
for	O
more	O
problematic	O
disorders	O
of	O
binocular	B-Algorithm
vision	I-Algorithm
,	O
the	O
tropias	O
.	O
</s>
<s>
Binocular	B-Algorithm
vision	I-Algorithm
anomalies	O
include	O
:	O
diplopia	O
(	O
double	O
vision	O
)	O
,	O
visual	O
confusion	O
(	O
the	O
perception	O
of	O
two	O
different	O
images	O
superimposed	O
onto	O
the	O
same	O
space	O
)	O
,	O
suppression	O
(	O
where	O
the	O
brain	O
ignores	O
all	O
or	O
part	O
of	O
one	O
eye	O
's	O
visual	O
field	O
)	O
,	O
horror	O
fusionis	O
(	O
an	O
active	O
avoidance	O
of	O
fusion	O
by	O
eye	O
misalignment	O
)	O
,	O
and	O
anomalous	O
retinal	O
correspondence	O
(	O
where	O
the	O
brain	O
associates	O
the	O
fovea	O
of	O
one	O
eye	O
with	O
an	O
extrafoveal	O
area	O
of	O
the	O
other	O
eye	O
)	O
.	O
</s>
<s>
Binocular	B-Algorithm
vision	I-Algorithm
anomalies	O
are	O
among	O
the	O
most	O
common	O
visual	O
disorders	O
.	O
</s>
<s>
About	O
20%	O
of	O
patients	O
who	O
come	O
to	O
optometry	O
clinics	O
will	O
have	O
binocular	B-Algorithm
vision	I-Algorithm
anomalies	O
.	O
</s>
<s>
This	O
could	O
lead	O
to	O
various	O
binocular	B-Algorithm
vision	I-Algorithm
anomalies	O
(	O
such	O
as	O
reduced	O
amplitudes	O
of	O
accommodation	O
,	O
accommodative	O
facility	O
,	O
and	O
positive	O
fusional	O
vergence	B-Algorithm
both	O
at	O
near	O
and	O
distance	O
)	O
.	O
</s>
<s>
If	O
,	O
however	O
,	O
defects	O
of	O
binocular	B-Algorithm
vision	I-Algorithm
are	O
too	O
great	O
–	O
for	O
example	O
if	O
they	O
would	O
require	O
the	O
visual	O
system	O
to	O
adapt	O
to	O
overly	O
large	O
horizontal	O
,	O
vertical	O
,	O
torsional	O
or	O
aniseikonic	O
deviations	O
–	O
the	O
eyes	O
tend	O
to	O
avoid	O
binocular	B-Algorithm
vision	I-Algorithm
,	O
ultimately	O
causing	O
or	O
worsening	O
a	O
condition	O
of	O
strabismus	O
.	O
</s>
