<s>
Cyclovergence	B-Algorithm
is	O
the	O
simultaneous	O
occurring	O
cyclorotation	O
(	O
torsional	O
movement	O
)	O
of	O
both	O
eyes	O
which	O
is	O
performed	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>
In	O
particular	O
,	O
in	O
the	O
presence	O
of	O
cyclodisparity	B-Algorithm
(	O
that	O
is	O
,	O
when	O
two	O
images	O
are	O
presented	O
which	O
would	O
need	O
to	O
be	O
rotated	O
in	O
relation	O
to	O
each	O
other	O
in	O
order	O
to	O
allow	O
visual	O
fusion	O
to	O
take	O
place	O
)	O
,	O
the	O
eyes	O
perform	O
cyclovergence	B-Algorithm
,	O
rotating	O
around	O
their	O
gaze	O
directions	O
in	O
opposite	O
directions	O
,	O
as	O
a	O
motor	O
response	O
to	O
cyclodisparity	B-Algorithm
.	O
</s>
<s>
Such	O
additional	O
,	O
visually	O
evoked	O
cyclovergence	B-Algorithm
appears	O
to	O
superimpose	O
linearly	O
onto	O
the	O
cycloversion	O
due	O
to	O
Listing	O
's	O
law	O
.	O
</s>
<s>
Visually	O
induced	O
cyclovergence	B-Algorithm
of	O
up	O
to	O
8	O
degrees	O
has	O
been	O
observed	O
in	O
normal	O
subjects	O
.	O
</s>
<s>
Together	O
with	O
the	O
8	O
degrees	O
that	O
can	O
usually	O
be	O
compensated	O
by	O
sensory	O
means	O
,	O
this	O
means	O
that	O
the	O
normal	O
human	O
observer	O
can	O
achieve	O
binocular	O
image	O
fusion	O
in	O
presence	O
of	O
cyclodisparity	B-Algorithm
(	O
also	O
called	O
orientation	O
disparity	O
in	O
the	O
case	O
of	O
a	O
line	O
image	O
)	O
of	O
up	O
to	O
approximately	O
16	O
degrees	O
.	O
</s>
<s>
Larger	O
cyclodisparity	B-Algorithm
normally	O
results	O
in	O
double	O
vision	O
.	O
</s>
<s>
It	O
has	O
been	O
shown	O
that	O
the	O
tolerance	O
of	O
human	O
stereopsis	O
to	O
cyclodisparity	B-Algorithm
of	O
lines	O
(	O
orientation	O
disparity	O
)	O
is	O
greater	O
for	O
vertical	O
lines	O
than	O
for	O
horizontal	O
lines	O
.	O
</s>
<s>
The	O
visually	O
evoked	O
cyclovergence	B-Algorithm
relaxes	O
once	O
the	O
cyclodisparity	B-Algorithm
is	O
reduced	O
to	O
zero	O
.	O
</s>
<s>
The	O
effect	O
also	O
relaxes	O
when	O
the	O
eyes	O
are	O
presented	O
with	O
darkness	O
;	O
however	O
,	O
experiments	O
show	O
that	O
in	O
the	O
latter	O
case	O
the	O
cyclovergence	B-Algorithm
does	O
not	O
disappear	O
completely	O
straight	O
away	O
.	O
</s>
<s>
Cyclovergence	B-Algorithm
can	O
also	O
be	O
evoked	O
by	O
cyclodisparity	B-Algorithm
of	O
the	O
visual	O
field	O
;	O
the	O
cyclodisparity	B-Algorithm
can	O
be	O
introduced	O
by	O
dove	O
prisms	O
.	O
</s>
<s>
Conversely	O
,	O
the	O
range	O
of	O
cyclovergence-based	O
cyclofusion	O
can	O
be	O
trained	O
using	O
dove	O
prisms	O
that	O
actively	O
rotate	O
the	O
field	O
of	O
view	O
:	O
"	O
The	O
patient	O
fixates	O
a	O
vertical	O
line	O
target	O
,	O
and	O
the	O
dove	O
prism	O
is	O
rotated	O
in	O
the	O
direction	O
to	O
increase	O
the	O
action	O
of	O
the	O
insufficient	O
muscle	O
while	O
fusion	O
is	O
maintained.	O
"	O
</s>
<s>
However	O
,	O
for	O
a	O
long	O
time	O
the	O
mechanism	O
of	O
the	O
compensation	O
was	O
unclear	O
:	O
many	O
thought	O
that	O
cyclofusion	O
was	O
due	O
exclusively	O
to	O
high-level	O
processing	O
of	O
the	O
visual	O
images	O
,	O
while	O
others	O
suggested	O
a	O
motor	O
cyclovergence	B-Algorithm
response	O
.	O
</s>
<s>
In	O
1975	O
,	O
motor	O
cyclovergence	B-Algorithm
was	O
demonstrated	O
for	O
the	O
first	O
time	O
with	O
photographic	O
methods	O
.	O
</s>
<s>
Cyclovergence	B-Algorithm
,	O
and	O
more	O
generally	O
torsional	O
eye	O
positions	O
,	O
can	O
be	O
measured	O
using	O
scleral	O
coils	O
or	O
using	O
video-oculography	B-Algorithm
.	O
</s>
<s>
There	O
have	O
been	O
contradictory	O
statements	O
on	O
whether	O
cyclovergence	B-Algorithm
can	O
be	O
measured	O
subjectively	O
,	O
that	O
is	O
,	O
by	O
an	O
evaluation	O
of	O
the	O
subjects	O
 '	O
own	O
statements	O
on	O
whether	O
lines	O
in	O
a	O
scene	O
appear	O
at	O
an	O
angle	O
in	O
the	O
two	O
eyes	O
.	O
</s>
<s>
Recent	O
evidence	O
based	O
on	O
an	O
analysis	O
of	O
the	O
empirical	O
horopter	O
suggests	O
that	O
subjective	O
estimates	O
of	O
cyclovergence	B-Algorithm
are	O
accurate	O
if	O
they	O
are	O
performed	O
using	O
horizontal	O
lines	O
to	O
the	O
left	O
and	O
to	O
the	O
right	O
of	O
the	O
fixation	O
,	O
not	O
vertical	O
lines	O
above	O
and	O
below	O
it	O
which	O
would	O
be	O
affected	O
by	O
shear	B-Algorithm
of	O
retinal	O
correspondence	O
points	O
.	O
</s>
