Correlation of morphologic features of the iridocorneal angle to intraocular pressure in Samoyeds


Ekesten, B.; Narfström, K.

American Journal of Veterinary Research 52(11): 1875-1878

1991


The iridocorneal angle of the left eye was investigated in 203 Samoyeds. Comparison was made of judgements of the width of the anterior opening of the ciliary cleft when performing gonioscopy with an objective method of estimation based on measurements on goniophotographs. Results indicated high degree of correlation. Various degrees of narrowness of the iridocorneal angle width were revealed and clinical glaucoma with total-angle closure was found in 6 of 203 dogs. The intraocular pressure was significantly (P less than 0.01) higher in eyes with closed iridocorneal angles than in eyes with any other width of the angle. Appearance of the structures of the iridocorneal angle, particularly the pigment bands, indicated extensive individual variation. In approximately 25% of the eyes, dysplasia of the pectinate ligaments of variable degree existed, indicating that this anomaly is common in the Samoyed breed. Significant difference was not evident in intraocular pressure in eyes with different degrees of dysplasia of the pectinate ligaments.

Correlation
of
morphologic
features
of
the
iridocorneal
angle
to
intraocular
pressure
in
Samoyeds
Bjorn
Ekesten,
DVM,
and
Kristina
Narfstrom,
DVM,
PhD
SUMMARY
The
iridocorneal
angle
of
the
left
eye
was
investigated
in
203
Samoyeds.
Comparison
was
made
of
judgements
of
the
width
of
the
anterior
opening
of
the
ciliary
cleft
when
performing
gonioscopy
with
an
objective
method
of
estimation
based
on
measurements
on
goniophotographs.
Results
indicated
high
degree
of
correlation.
Various
de-
grees
of
narrowness
of
the
iridocorneal
angle
width
were
revealed
and
clinical
glaucoma
with
total-angle
closure
was
found
in
6
of
203
dogs.
The
intraocular
pressure
was
significantly
(P
<
0.01)
higher
in
eyes
with
closed
irido-
corneal
angles
than
in
eyes
with
any
other
width
of
the
angle.
Appearance
of
the
structures
of
the
iridocorneal
angle,
particularly
the
pigment
bands,
indicated
exten-
sive
individual
variation.
In
approximately
25%
of
the
eyes,
dysplasia
of
the
pectinate
ligaments
of
variable
de-
gree
existed,
indicating
that
this
anomaly
is
common
in
the
Samoyed
breed.
Significant
difference
was
not
evi-
dent
in
intraocular
pressure
in
eyes
with
different
de-
grees
of
dysplasia
of
the
pectinate
ligaments.
Intraocular
pressure
(Kw)
is
maintained
by
a
dynamic
equilibrium
between
production
and
outflow
of
aqueous
humor.
The
major
route
of
aqueous
drainage
in
mammals
is
through
the
iridocorneal
angle
in
the
anterior
chamber
of
the
eye,
and
only
small
volumes
are
eliminated
through
other
means.
1
'
2
The
iridocorneal
angle
in
dogs
is
limited
by
the
base
of
the
iris,
the
anterior
part
of
the
ciliary
body,
the
anterior
inner
surface
of
the
sclera,
and
the
interior
of
the
peripheral
cornea.
A
row
of
thin
processes,
the
pectinate
ligaments,
spans
the
anterior
opening
of
the
iridocorneal
angle.
Between
these
ligaments
are
distinct
spaces,
which
lead
to
the
more
posterior
parts
of
the
cil-
iary
cleft.
3,4
Aberrations
in
the
iridocorneal
angle
are
of
great
importance
because
it
is
postulated
that
they
may
impair
the
outflow
of
the
aqueous
humor
and
cause
in-
traocular
hypertension,
which
will,
if
permanent,
result
in
glaucoma.
5,5-7
Primary
glaucomas
associated
with
an-
gle
closure,
dysplastic
pectinate
ligaments,
or
combina-
tions
of
these
anomalies
have
been
reported
in
several
breeds.
3,6-10
In
the
Samoyed
breed,
primary
glaucoma
is
considered
to
develop
because
of
angle
closure
or
a
congenital
defect
in
the
iridocorneal
angle,
goniodysgenesis.
11,12
The
ap-
Received
for
publication
June
11,
1990,
From
the
Department
of
Medicine
and
Surgery,
Faculty
of
Veterinary
Medicine,
Swedish
University
of
Agricultural
Sciences,
S-750
07
Uppsala,
Sweden.
Supported
in
part
by
a
grant
from
the
Thure
F
and
Karin
Forsberg
Foundation,
Stockholm,
Sweden,
The
authors
thank
Swedish
breeders
and
owners
of
Samoyed
dogs
for
assistance,
pearance
of
the
anterior
parts
the
canine
iridocorneal
angle
can
easily
be
viewed.
and
documented
in
vivo
by
gonioscopy
and
goniophotography.
13
'
14
The
degree
of
de-
flection
in
width
of
the
anterior
opening
of
the
ciliary
cleft
and
appearance
of
the
pectinate
ligaments
is
judged
sub-
jectively
by
the
examiner.
A
method
of
estimating
the
width
of
the
anterior
opening
of
the
ciliary
cleft
by
com-
paring
the
width
of
the
anterior
opening
of
the
ciliary
cleft
to
the
peripheral
thickness
of
the
cornea
is
used
in
human
ophthalmology.
This
comparison
between
2
dis-
tances
at
the
same
level
in
the
eye
simplifies
the
esti-
mation
of
the
width
of
the
anterior
opening
of
the
ciliary
cleft.
15
The
distribution
of
dysplastic
pectinate
ligaments
can
be
estimated
in
fractions
of
the
circumference.
16
The
purposes
of
the
study
reported
here
were
to
inves-
tigate
the
possibilities
of
measuring
the
width
of
the
ca-
nine
iridocorneal
angle
(ie,
the
width
of
the
anterior
opening
of
the
ciliary
cleft)
in
an
objective
way
and
to
map
the
appearance
of
the
iridocorneal
angle
in
Sa-
moyeds.
Also,
we
wished
to
elucidate
whether
correlation
exists
between
high
IOP
and
narrow
or
dysplastic
irido-
corneal
angle.
Materials
and
Methods
Dogs
and
ophthalmic
examinations—The
study
in-
cluded
203
purebred
Samoyeds,
111
female
and
92
male,
aged
4
months
to
13
years.
After
general
clinical
exam-
ination
of
the
dogs,
direct
and
indirect
ophthalmoscopy,
slit-lamp
biomicroscopy,
and
tonometrya
were
performed
on
both
eyes
(nondilated
pupils)
in
the
order
mentioned.
Gonioscopyb
was
performed
as
the
last
procedure,
for
practical
reasons,
only
on
the
left
eye
of
each
dog.
In
3
dogs,
the
left
eye
had
been
enucleated
because
of
high
IOP
and
gonioscopy
was,
therefore,
performed
on
the
right
eye.
Results
were
documented
in
writing,
and
goniopho-
tographsa
were
taken
of
the
nasal
aspect
of
the
iridocor-
neal
angle.
In
cases
of
heterogeneous
appearance
of
the
angle,
other
parts
were
documented
as
well.
All
exami-
nations
were
performed
on
conscious,
nonsedated
dogs.
Measurements—The
width
of
the
iridocorneal
angle,
as
well
as
the
distribution
of
dysplastic
pectinate
ligaments,
was
estimated
subjectively.
The
anterior
width
of
the
cil-
iary
cleft
(the
distance
from
the
origin
to
the
insertion
of
the
pectinate
ligamentss)
and
the
total
distance
from
the
origin
of
the
pectinate
ligaments
to
the
anterior
corneal
surface
was
measured
from
the
goniophotographs.
The
ratio
between
these
2
variables
was
then
calculated.
The
basis
for
grading
the
anterior
width
was
determined
(Fig
Tono-Pen
2,
Oculab
Inc,
Glendale,
Calif.
b
Barkan
Lovac,
Medical
Workshop,
Groningen,
The
Netherlands.
Kowa
RC-2,
Kowa
Co
Ltd,
Tokyo,
Japan.
Am
J
Vet
Res,
Vol
52,
No.
11,
November
1991
1875
„,,
I
I
BA
A
BA
BA
BA
Terminology
Closed
Numerical
grade
0
Relabye
interval
(x=A/B)
,
x50.15
Narrow
0.15<x0.30
Slightly
narrow
II
0.80<x50.45
Open
III
0
45.0
55
Wide
open
Iv
0.55.‘x
EFGH
a
Figure
1
—Schematic
drawing
representing
the
grading
system
for
width
of
the
iridocorneal
an-
gle.
The
width
of
the
anterior
opening
of
the
ciliary
cleft
(A)
and
the
distance
from
the
origin
of
the
pectinate
ligaments
to
the
anterior
surface
of
the
cornea
(B)
are
measured
from
goniopho-
tographs
and
the
quote
is
calculated.
Pupil
(C);
iris
(D);
pectinate
ligament
(E);
deep
band
of
the
pigment
zone
(F);
superficial
band
of
the
pig-
ment
zone
(G);
and
cornea
(H).
Figure
2—Schematic
drawing
of
dysplastic
pectinate
ligaments
(black).
The
arrow
(with
a
perpendicular
bar
every
1/16
of
the
circumference
of
the
iridocorneal
angle)
indicates
extension
of
the
dysplasia.
1).
A
pectinate
ligament
was
considered
to
be
dysplastic
if
it
extended
over
more
than
1/16
of
the
circumference
without
being
interrupted
by
normal
interligamentary
spaces
(Fig
2).
The
extension
was
subjectively
estimated
by
the
examiner.
Analysis
of
data—The
Student
t
test
was
used
to
de-
termine
statistical
significance.
Results
Major
ophthalmoscopic
and
slit-lamp
biomicroscopic
abnormalities
were
discovered
in
6
dogs
with
clinical
glaucoma.
Secondary
complete
bilateral
cataracts
were
observed
in
a
6-year-old
bitch
with
chronic
diabetes
mel-
litus.
The
degree
of
pigmentation
in
the
superficial
and
Figure
3—Normal
iridocorneal
angle
in
a
6-month-old
normotensive
male
Samoyed.
The
origin
of
the
pectinate
ligaments
is
conical
and
lateral
branching
can
be
observed
frequently
near
the
insertion.
Notice
distinct
interligamentary
spaces.
Neither
the
superficial
nor
deep
band
of
the
pig-
ment
zone
is
discernible
in
this
part
of
the
eye.
Arrows
indicate
the
anterior
border
of
the
peripheral
corneal
transaction.
deep
bands
of
the
pigment
zone,
as
well
as
pigmentation
of
the
structures
in
the
iridocorneal
angle,
varied
exten-
sively
between
eyes
of
various
dogs,
but
often
a
difference
was
apparent
between
parts
of
the
circumference
within
the
same
eye.
The
pectinate
ligaments
were
generally
more
heavily
pigmented
than
the
peripheral
part
of
the
iris.
The
site
of
insertion
on
the
cornea
was
usually
marked
by
a
distinct
deep
band
of
pigment.
In
one
dog,
the
par-
tially
blue
iris
was
extremely
poorly
pigmented
and
bands
of
pigment
were
not
discernible.
The
pectinate
ligaments
had
extensive
variation
in
width
and
form,
not
only
in
different
dogs,
but
also
in
different
parts
of
the
same
eye.
Lateral
branching
(except
at
the
site
of
insertion)
and
crossing
over
of
primary
pectinate
ligaments
were
seen
in
a
few
eyes
(Fig
3).
Iridal
strands
anterior
to
the
rows
of
pectinate
ligaments
were
seen
in
one
dog.
Dysplasia
of
the
pectinate
ligaments
was
seen
in
many
dogs.
Multiple
minor
areas
of
dysplasia
spread
around
the
1876
Am
J
Vet
Res,
Vol
52,
No.
11,
November
1991
Figure
4—The
anterior
opening
of
the
iridocorneal
angle
in
a
5.6-year-old
normotensive
Samoyed
bitch.
Partial
dysplasia
of
the
pectinate
ligaments
can
be
observed.
Only
a
single
crater-shaped
opening
(arrow)
can
be
found
in
the
dysplastic
area.
The
pigmegt
bands
cannot
be
seen
in
this
part
of
the
eye.
Figure
5—Closed
iridocorneal
angle
in
a
3.9-year-old
male
Samoyed
with
glaucoma.
The
anterior opening
of
the
iridocorneal
angle
cannot
be
ex-
amined.
Arrows
indicate
the
borders
of
the
peripheral
corneal
transection.
The
photograph
is
indistinct
owing
to
corneal
edema.
circumference
were
observed,
as
well
as
larger,
continu-
ous
bands
(Fig
4).
Dysplastic
pectinate
ligaments
were
found
in
49
of
198
eyes
examined
(24.7%).
In
16
(8.1%)
of
these
eyes
more
than
half
the
circumference
was
covered
by
dysplastic
ligaments.
In
6
eyes,
the
iridocorneal
angle
was
so
narrow
that
the
anterior
region
of
the
angle
could
not
be
thoroughly
examined
(Fig
5).
The
open
spaces
between
the
pectinate
ligaments
often
varied
substantially
within
an
eye.
Distinct
openings
of
the
same
length
as
the
pectinate
ligaments
were
usually
seen
in
areas
without
dysplastic
pectinate
ligaments.
In
areas
with
dysplasia,
the
interligamentary
spaces
were
slit-like,
or
more
commonly,
were
crater-shaped,
round
holes
(Fig
6).
The
diameter
of
these
holes
was
often
con-
siderably
less
than
the
width
of
the
angle.
In
2
dogs,
the
Figure
6—Narrow
iridocorneal
angle
(grade
1)
and
generalized
dysplasia
of
the
pectinate
ligaments
in
a
9.8-year-old
normotensive
male
Samoyed.
Several
slit-like
openings
can
be
observed
(arrows).
A
pigmented
zone
Is
seen
anterior
to
the
insertion
of
the
dysplastic
sheath,
but
distinct
division
into
a
superficial
and
a
deep
band
is
not
possible.
Table
1—Width
of
the
iridocorneal
angle
in
203
Samoyeds
(204
eyes)
estimated
by
subjective
judgement
and
as
a
ratio
between
the
width
of
the
anterior
opening
and
the
distance
from
the
origin
of
the
pectinate
ligaments
to
the
peripheral
anterior
surface
of
the
cornea
Measurement
(numerical
grade)
Subjective
judgement
o
I
II
III
ry
6
0
0 0 0
0
12
1
0 0
II
0
0
47
4
0
III
0
0
1
112
1
IV
0
0 0
1
18
pectinate
ligaments
were
normally
differentiated,
but
an
almost
solid
sheath
of
tissue
was
located
caudal
to
the
rows
of
pectinate
ligaments.
This
sheath
did
not
appear
to
encircle
the
whole
circumference
in
any
case
and
it
was
interrupted
by
a
small
number
of
large
flow
holes.
The
diameter
of
the
flow
holes
varied
from
a
third
to
two-
thirds
the
length
of
the
pectinate
ligaments.
Results
of
grading
the
anterior
width
of
ciliary
clefts
were
obtained
in
5
groups,
using
both
methods
of
esti-
mation
(Table
1).
Comparison
of
these
methods
indicates
that
dissimilarities
developed
in
approximately
4.4%
of
the
dogs.
Furthermore,
statistical
analysis
proved
that
dissimilarities
between
the
methods
were
not
significant.
All
dogs
with
clinical
glaucoma
were
found
in
group
0,
using
both
methods
of
estimation.
Intraocular
pressure
of
the
gonioscopically
examined
eyes
was
related
to
the
anterior
width
of
the
ciliary
cleft
and
a
comparison
of
the
intraocular
pressure
was
made
between
the
5
numerical
grades
(Fig
1).
Mean
SD)
IOP
was
significantly
higher
(P
<
0.01)
in
eyes
with
closed
iridocorneal
angles
(40
±
11
mm
of
Hg)
than
in
any
of
the
other
groups
(15
±
3.8
mm
of
Hg).
Significant
differ-
ences
in
IOP
were
not
evident
when
the
groups
graded
1
to
4
were
compared.
To
determine
whether
relationship
existed
between
IOP
and
the
degree
of
dysplasia
of
pec-
tinate
ligaments
in
gonioscopically
examined
eyes,
the
Am
J
Vet
Res,
Vol
52,
No.
11,
November
1991
1877
aforementioned
variables
were
compared.
Significant
dif-
ferences
were
not
found,
however.
Discussion
The
iridocorneal
angle
in
Samoyeds
has
great
morpho-
logic
variation
between
eyes
of
individuals
and
between
different
parts
of
the
circumference
in
the
same
eye.
In-
dividual
variation
included
essentially
the
degree
and
distribution
of
pigmentation,
width
of
the
pectinate
lig-
aments,
and
width
and
frequency
of
the
openings
to
the
ciliary
cleft.
The
anterior
width
of
the
ciliary
cleft
was
considerably
more
constant
within
the
same
eye,
but
var-
iation
between
dogs
was
pronounced.
We
also
docu-
mented
that
dysplasia
of
pectinate
ligaments
is
a
common
finding
in
Samoyeds
in
Sweden.
Minor
dysplastic
strands
could
be
seen
in
most
dogs
5
and
were
considered
normal
in
this
study.
Correlation
was
not
found
between
the
ex-
tension
of
pectinate
ligaments
and
IOP.
Thus,
dysplasia
of
pectinate
ligaments,
even
in
cases
of
comprehensive
extension,
is
not
sufficient
to
cause
permanent
intraocu-
lar
hypertension.
Narrowed
and
closed
iridocorneal
angles,
the
latter
in
cases
of
acute
clinical
glaucoma,
indicate
that
angle-clo-
sure
glaucomas
do
develop
in
this
breed.
The
IOP
was
significantly
higher
only
in
eyes
with
closed
iridocorneal
angles
and
not
in
eyes
with
variation
in
the
anterior
width
of
the
ciliary
cleft,
with
or
without
dysplasia
of
the
pec-
tinate
ligaments.
Lack
of
high
IOP
in
cases
of
narrow,
but
still
open,
iridocorneal
angles
indicates
that
other
initi-
ating
factors
must
be
present
to
further
impair
the
out-
flow
of
aqueous,
resulting
in
clinical
glaucoma.
It
is,
however,
important
to
know
the
normal
variation
of
the
iridocorneal
angle
in
a
breed
and
to
be
able
to
observe
alterations
of
this
structure
in
dogs
of
predisposed
breeds.
Our
results
indicate
that
a
method
based
on
calculating
the
ratio
between
the
length
of
the
pectinate
ligaments
and
the
distance
from
the
origin
of
the
pectinate
liga-
ments
to
the
anterior
surface
of
the
peripheral
part
of
the
cornea
after
measurements
on
goniophotographs
agrees
well
with
the
grading
method
obtained
by
direct,
subjec-
tive
estimation
of
the
width
of
the
iridocorneal
angle.
One
advantage
of
the
former
method
is
that
a
minimum
of
experience
is
needed
to
measure
the
aforementioned
structures
by
means
of
goniophotographs.
The
calculated
value
is
a
ratio
between
2
structures
at
the
same
level,
which
then
becomes
almost
independent
of
different
mag-
nifications
and
the
angle
between
the
film
and
the
iri-
docorneal
angle.
References
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KP,
Gum
GG,
Samuelson
DA,
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al.
Quantitation
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Beagles
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3
H-la-
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