<s>
A	O
vergence	B-Algorithm
is	O
the	O
simultaneous	O
movement	O
of	O
both	O
eyes	O
in	O
opposite	O
directions	O
to	O
obtain	O
or	O
maintain	O
single	B-Algorithm
binocular	I-Algorithm
vision	I-Algorithm
.	O
</s>
<s>
When	O
a	O
creature	O
with	O
binocular	B-Algorithm
vision	I-Algorithm
looks	O
at	O
an	O
object	O
,	O
the	O
eyes	O
must	O
rotate	O
around	O
a	O
vertical	O
axis	O
so	O
that	O
the	O
projection	O
of	O
the	O
image	O
is	O
in	O
the	O
centre	O
of	O
the	O
retina	O
in	O
both	O
eyes	O
.	O
</s>
<s>
Vergence	B-Algorithm
movements	O
are	O
closely	O
connected	O
to	O
accommodation	O
of	O
the	O
eye	O
.	O
</s>
<s>
Under	O
normal	O
visual	O
conditions	O
,	O
looking	O
at	O
an	O
object	O
at	O
a	O
different	O
distance	O
will	O
automatically	O
cause	O
changes	O
in	O
both	O
vergence	B-Algorithm
and	O
accommodation	O
,	O
sometimes	O
known	O
as	O
the	O
accommodation-convergence	O
reflex	O
.	O
</s>
<s>
When	O
under	O
non-typical	O
visual	O
conditions	O
like	O
when	O
looking	O
at	O
a	O
stereogram	B-Algorithm
,	O
the	O
vergence	B-Algorithm
and	O
accommodation	O
of	O
the	O
eyes	O
will	O
not	O
match	O
,	O
resulting	O
in	O
the	O
viewer	O
experiencing	O
the	O
vergence-accommodation	O
conflict	O
.	O
</s>
<s>
As	O
opposed	O
to	O
the	O
500°	O
/s	O
velocity	O
of	O
saccade	O
movements	O
,	O
vergence	B-Algorithm
movements	O
are	O
far	O
slower	O
,	O
around	O
25°	O
/s	O
.	O
</s>
<s>
The	O
following	O
types	O
of	O
vergence	B-Algorithm
are	O
considered	O
to	O
act	O
in	O
superposition	O
:	O
</s>
<s>
Tonic	O
vergence	B-Algorithm
:	O
vergence	B-Algorithm
due	O
to	O
normal	O
extraocular	O
muscle	O
tone	O
,	O
with	O
no	O
accommodation	O
and	O
no	O
stimulus	O
to	O
binocular	B-Algorithm
fusion	I-Algorithm
.	O
</s>
<s>
Tonic	O
vergence	B-Algorithm
is	O
considered	O
to	O
move	O
the	O
eyes	O
from	O
an	O
anatomical	O
position	O
of	O
rest	O
(	O
which	O
would	O
be	O
the	O
eye	O
's	O
position	O
if	O
it	O
were	O
not	O
innervated	O
)	O
to	O
the	O
physiological	O
position	O
of	O
rest	O
.	O
</s>
<s>
Accommodative	O
vergence	B-Algorithm
:	O
blur-driven	O
vergence	B-Algorithm
.	O
</s>
<s>
Fusional	O
vergence	B-Algorithm
(	O
also	O
:	O
disparity	O
vergence	B-Algorithm
,	O
disparity-driven	O
vergence	B-Algorithm
,	O
or	O
reflex	O
vergence	B-Algorithm
)	O
:	O
vergence	B-Algorithm
induced	O
by	O
a	O
stimulus	O
to	O
binocular	B-Algorithm
fusion	I-Algorithm
.	O
</s>
<s>
Proximal	O
vergence	B-Algorithm
:	O
vergence	B-Algorithm
due	O
to	O
the	O
awareness	O
of	O
a	O
fixation	O
object	O
being	O
near	O
or	O
far	O
in	O
the	O
absence	O
of	O
disparity	O
and	O
of	O
cues	O
for	O
accommodation	O
.	O
</s>
<s>
This	O
includes	O
also	O
vergence	B-Algorithm
that	O
is	O
due	O
to	O
a	O
subject	O
's	O
intent	O
to	O
fixate	O
an	O
object	O
in	O
the	O
dark	O
.	O
</s>
<s>
Accommodative	O
vergence	B-Algorithm
is	O
measured	O
as	O
the	O
ratio	O
between	O
how	O
much	O
convergence	O
takes	O
place	O
for	O
a	O
given	O
accommodation	O
(	O
AC/A	O
ratio	O
,	O
CA/C	O
ratio	O
)	O
.	O
</s>
<s>
Proximal	O
vergence	B-Algorithm
is	O
sometimes	O
also	O
called	O
voluntary	O
vergence	B-Algorithm
,	O
which	O
however	O
more	O
generally	O
means	O
vergence	B-Algorithm
under	O
voluntary	O
control	O
and	O
is	O
sometimes	O
considered	O
a	O
fifth	O
type	O
of	O
vergence	B-Algorithm
.	O
</s>
<s>
Voluntary	O
vergence	B-Algorithm
is	O
also	O
required	O
for	O
viewing	O
autostereograms	B-Algorithm
as	O
well	O
as	O
for	O
voluntary	O
crossing	O
of	O
the	O
eyes	O
.	O
</s>
<s>
Voluntary	O
convergence	O
is	O
normally	O
accompanied	O
by	O
accommodation	O
and	O
miosis	O
(	O
constriction	O
of	O
the	O
pupil	O
)	O
;	O
often	O
however	O
,	O
with	O
extended	O
practice	O
,	O
individuals	O
can	O
learn	O
to	O
dissociate	O
accommodation	O
and	O
vergence	B-Algorithm
.	O
</s>
<s>
Vergence	B-Algorithm
is	O
also	O
denoted	O
according	O
to	O
its	O
direction	O
:	O
horizontal	O
vergence	B-Algorithm
,	O
vertical	O
vergence	B-Algorithm
,	O
and	O
torsional	O
vergence	B-Algorithm
(	O
cyclovergence	B-Algorithm
)	O
.	O
</s>
<s>
Horizontal	O
vergence	B-Algorithm
is	O
further	O
distinguished	O
into	O
convergence	O
(	O
also	O
:	O
positive	O
vergence	B-Algorithm
)	O
or	O
divergence	O
(	O
also	O
:	O
negative	O
vergence	B-Algorithm
)	O
.	O
</s>
<s>
Vergence	B-Algorithm
eye	I-Algorithm
movements	O
result	O
from	O
the	O
activity	O
of	O
six	O
extraocular	O
muscles	O
.	O
</s>
<s>
Horizontal	O
vergence	B-Algorithm
involves	O
mainly	O
the	O
medial	O
and	O
lateral	O
rectus	O
.	O
</s>
<s>
In	O
ophthalmology	O
,	O
convergence	O
is	O
the	O
simultaneous	O
inward	O
movement	O
of	O
both	O
eyes	O
toward	O
each	O
other	O
,	O
usually	O
in	O
an	O
effort	O
to	O
maintain	O
single	B-Algorithm
binocular	I-Algorithm
vision	I-Algorithm
when	O
viewing	O
an	O
object	O
.	O
</s>
<s>
It	O
is	O
a	O
type	O
of	O
vergence	B-Algorithm
eye	I-Algorithm
movement	O
and	O
is	O
done	O
by	O
extrinsic	O
muscles	O
.	O
</s>
<s>
Convergence	B-Algorithm
insufficiency	I-Algorithm
is	O
a	O
common	O
problem	O
with	O
the	O
eyes	O
,	O
and	O
is	O
the	O
main	O
culprit	O
behind	O
eyestrain	O
,	O
blurred	O
vision	O
,	O
and	O
headaches	O
.	O
</s>
<s>
In	O
ophthalmology	O
,	O
divergence	O
is	O
the	O
simultaneous	O
outward	O
movement	O
of	O
both	O
eyes	O
away	O
from	O
each	O
other	O
,	O
usually	O
in	O
an	O
effort	O
to	O
maintain	O
single	B-Algorithm
binocular	I-Algorithm
vision	I-Algorithm
when	O
viewing	O
an	O
object	O
.	O
</s>
<s>
It	O
is	O
a	O
type	O
of	O
vergence	B-Algorithm
eye	I-Algorithm
movement	O
.	O
</s>
<s>
A	O
number	O
of	O
vergence	B-Algorithm
dysfunctions	O
exist	O
:	O
</s>
<s>
Vergence	B-Algorithm
control	O
,	O
and	O
over-convergence	O
associated	O
with	O
the	O
extra	O
accommodation	O
required	O
to	O
overcome	O
a	O
hyperopic	O
refractive	O
error	O
,	O
play	O
a	O
role	O
in	O
the	O
onset	O
of	O
accommodative	O
esotropia	O
.	O
</s>
<s>
It	O
is	O
an	O
active	O
area	O
of	O
research	O
to	O
understand	O
the	O
reasons	O
why	O
many	O
infants	O
with	O
hyperopia	O
develop	O
accommodative	O
esotropia	O
whereas	O
others	O
do	O
not	O
,	O
and	O
which	O
is	O
the	O
exact	O
influence	O
of	O
the	O
vergence	B-Algorithm
system	O
in	O
this	O
context	O
.	O
</s>
