International Journal of Clinical Medicine, 2013, 4, 548-555
Published Online December 2013 (http://www.scirp.org/journal/ijcm)
http://dx.doi.org/10.4236/ijcm.2013.412095
Open Access IJCM
Evaluation of Nasal and Temporal Anterior Chamber
Angle with Four Different Techniques
Fredrik P. Källmark, Mezghan Sakhi
Unit of Optometry, Section of Ophthalmology and Vision, Department of Clinical Neurosience, Karolinska Instetutet, Stockholm,
Sweden.
Received October 8th, 2013; revised November 5th, 2013; accepted December 2nd, 2013
Copyright © 2013 Fredrik P. Källmark, Mezghan Sakhi. This is an open access article distributed under the Creative Commons At-
tribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is prop-
erly cited.
ABSTRACT
Background: Anterior chamber angle (ACA) can be measured by many different techniques. In order for a technique
to be a part of the routine eye examination, it has to be quick and easy in good agreement with gonioscopy both nasally
and temporally. Aim: To investigate variation in ACA measurement between gonioscopy, van Herick technique, ante-
rior segment optical coherence tomography (AS-OCT) and Sirius Scheimpflug-Camera both nasally and temporally.
Method: The ACA of 50 eyes of 25 healthy subjects was measured with gonioscopy, van Herick technique, AS-OCT
and Sirius Scheimpflug-Camera. The angle was measured both nasally and temporally. Results: No statistically sig-
nificant difference could be found between gonioscopy, van Herick technique and AS-OCT either nasally or temporally.
The Sirius Scheimpflug-Camera on the other hand showed statistically significant difference to gonioscopy (p < 0.0001),
van Herick technique (p < 0.0001) and AS-OCT (p < 0.0001) both nasally (p = 0.03, p = 0.001, p < 0.0001) and tempo-
rally (p = 0.0002, p = 0.001, p < 0.0001). Conclusion: This study showed good agreement between three of the four
techniques. ACA measurements obtained by the Sirius Scheimpflug-Camera should therefore not be considered inter-
changeable with those obtained by the remaining three methods.
Keywords: Anterior Chamber Angle (ACA); Gonioscopy; Van Herick Technique; Sirius Scheimpflug Camera;
AS-OCT; Angle Closure Glaucoma
1. Introduction
Angle Closure Glaucoma (ACG), a sight threatening eye
disease, is a major cause of blindness throughout the
world [1].
ACG is caused by the abnormal positioning of the pe-
ripheral iris towards the trabecular meshwork which
hinders the aqueous outflow resulting in an increased
intraocular pressure (IOP), eventually leading to glauco-
matous optic neuropathy and irreversible blindness [2-4].
Eyes with narrow angles and at risk of ACG can be
prevented from the disease if they are identified prior to
the disease’s onset [5]. It is therefore very important to
measure and evaluate the anterior chamber angle (ACA),
Figure 1, of all the patients in a routine eye examination.
One should also evaluate the ACA of elderly patients as
the prevalence of ACG increases with age due to the
gradual increase of the crystalline lens [1,2,6]. Evalua-
tion of ACA should also be performed at patients who
take medication that can cause pupil dilation [7]. For
ACA evaluation in a routine eye examination, a quick
and easy method is needed.
ACA can be measured by many different methods: e.g.
gonioscopy, ultra sound biomicroscopy (UBM), van He-
rick technique, Scheimpflug photography, anterior seg-
ment optical coherence tomography (AS-OCT) and the
Sirius Scheimpflug-Camera [1].
1.1. Gonioscopy
Gonioscopy, the current gold standard method, makes
use of a slit lamp and a contact lens (gonioscopy lens) to
view the ACA structures. When describing the angle
with gonioscopy, several systems have been developed
as Scheie, Shaffer, Becker and Spaeth [8,10,11]. Pressure
on the gonioscopy lens and illumination used during the
examination can alter the angle configuration. Further-
more, it is a time consuming subjective method that re-

Evaluation of Nasal and Temporal Anterior Chamber Angle with Four Different Techniques 549
Figure 1. Diagram of the anatomical structures forming the
iridocorneal angle.
quires considerable skill, knowledge and experience in
order to achieve reliable measurements [1,3,4,12]. These
limitations make gonioscopy less suitable as a quick
evaluation method for ACA in a routine eye examination.
1.2. Van Herick
Van Herick technique, Sirius Scheimpflug-Camera and
AS-OCT on the other hand can be part of a routine eye
checkup as they all are quick and easy to perform and do
not contact the cornea [1,7].
The van Herick technique uses a slit lamp to subjec-
tively estimate the ACA whilst Sirius Scheimpflug-
Camera and AS-OCT provide objective measurement of
the ACA.
1.3. AS-OCT
AS-OCT is a tomographic and biomicroscopic device of
high resolution designed for imaging and measuring the
anterior segment of the eye [3]. Measurement of the
ACA by the AS-OCT takes less than a second. The AS-
OCT takes cross sectional images of the anterior segment
that are analyzed by a semiautomatic software program
that is connected to the device. The examiner marks the
apex of the angle, the posterior surface of the cornea and
the anterior surface of the iris and the software calculates
the ACA in degrees [3,13].
1.4. Sirius Scheimpflug-Camera
Sirius Scheimpflug-Camera is a combination of a 3D
rotating Scheimpflug camera with a placido disc topog-
rapher that gives a detailed evaluation of the entire ante-
rior eye segment including ACA. The scanning process
takes less than one second and acquires about 25 Sch-
eimpflug images, which are analyzed by the computer
software program that is connected to the device and the
ACA is presented in degrees [14].
2. Previous Comparisons
Good agreement between gonioscopy and the van Herick
technique is reported in a study by Kashiwagi et al. and
in another study by Foster et al. [15,16]. Conversely, in a
study by Thomas et al. the van Herick technique is said
to be in disagreement with gonioscopy because it meas-
ures the angle wider than gonioscopy [17]. AS-OCT is
reported to detect more closed ACAs than gonioscopy in
a study by Sakata et al. [18]. Patients with narrow angle
and those at risk of ACG can be missed if the angle is
measured wider than its real size. If the angle on the
other hand is measured narrower than its actual size, ad-
ditional evaluation by gonioscopy is required, which will
incur unnecessarily costs to the health care system. A
quick and accurate ACA evaluation method is therefore
necessary.
Since the Sirius Scheimpflug-Camera is a recently de-
veloped device, limited number of studies has been per-
formed on it. High repeatability for the anterior segment
measurement by the Sirius Scheimpflug-Camera is re-
ported in a study by Savini et al. [19]. However, the
study does not state anything about the repeatability of
the ACA measurement by the device. In addition, to the
best of our knowledge, no study comparing the Sirius
Scheimpflug-Camera to gonioscopy, the van Herick tech-
nique and the AS-OCT has yet been performed.
Most of the previous studies compare the temporal
ACA findings of van Herick technique to that of gonio-
scopy [5,12,13]. In a study by Pettersson and Källmark
and in another study by Friedman et al. significant dif-
ference between temporal and nasal ACA is reported
[1,20]. For an accurate comparison of ACA measuring
techniques, the angle should therefore be measured both
nasally and temporally as the techniques can be in
agreement nasally but in disagreement temporally or vice
versa.
Aims
The aim of this study was to investigate variation in
ACA measurement between gonioscopy, van Herick
technique, AS-OCT and Sirius Scheimpflug-Camera
both nasally and temporally
3. Methods and Material
3.1. Patients and Clinical Investigation
ACA of both eyes of 25 randomly selected subjects
(mean age 24.28 ± 3.77) were measured with all the four
methods (i.e. gonioscopy, van Herick technique, Sirius
Scheimpflug-Camera and AS-OCT). The study was per-
formed at S:t Erik Eye hospital and in accordance with
the declaration of Helsinki. Informed consent was ob-
tained from all the participants after they were well in-
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Evaluation of Nasal and Temporal Anterior Chamber Angle with Four Different Techniques
550
formed of the study’s nature. The ACA measurement
obtained with van Herick technique and gonioscopy was
carried out by an experienced optometrist masked to the
test results obtained by the Sirius Scheimpflug-Camera
and the AS-OCT. The Sirius Scheimpflug-Camera and
the AS-OCT measurements were performed by another
optometrist who was unaware of the gonioscopy and the
van Herick results. On the day the angle measures were
carried out, subjects had been free from contact lens
wear.
3.2. Van Herick Technique
ACA was measured both nasally and temporally with the
slit lamp using van Herick technique. The ACA was es-
timated by comparing the limbal anterior chamber depth
(LACD) (which was observed as an empty space be-
tween the corneal endothelium and the anterior iris) to
the corneal thickness. ACA was graded according to the
van Herick’s grading system which is illustrated in Table
1 [1,3,7,21].
3.3. Gonioscopy
Gonioscopy was performed using a Goldman 3-mirror
lens. The cornea was anesthetized using one drop of
0.4% oxybuprocaine hydrochloride. Two drops of 2%
methylcellulose were used as a coupling medium for the
gonioscopy lens. Care was taken to avoid accidental in-
dentation of the angle by direct illumination of the pupil
during the examination. Slight tilting of the lens was al-
lowed to gain view over the convexity of the iris. The
ACA was graded using Shaffer grading system which is
illustrated in Table 2 [1,4,6,13,22].
3.4. AC-OCT
The AS-OCT used in this study was Visante OCT manu-
factured by Carl Zeiss Meditec. The nasal and temporal
ACA can be measured simultaneously by the AS-OCT.
Images of the ACA were acquired with the subject seated
and fixating an internal fixation target. The subject was
instructed to blink and open his/her eye widely before
Table 1. ACA grading system as described by van Herik.
Width of the empty space
(LACD*) as compared to the
corneal thickness
van Herick
Grade Angle status
No black space observed 0 Closed
<1/4 Corneal thickness 1 Extremely narrow
1/4 of corneal thickness 2 Narrow
>1/4 to 1/2 of corneal thickness 3 Open
≥1 of corneal thickness 4 Wide open
*LACD = Limbal Anterior Chamber Depth.
Table 2. ACA grading system as described by Shaffer.
ACA*
in degrees ACA gradeAngle status Visible structures
0 0 Closed No structures visible
≤10 1 Extremely narrow Schwalbe’s line
11 - 19 2 Narrow Trabecular meshwork
20 - 34 3 Open Scleral spur
35 - 45 4 Wide open Ciliary body
*ACA = Anterior Chamber Angle.
each measurement. Acquired images were then analysed
using the semi-automated software programme provided
by the device.
3.5. Sirius Scheimpflug-Camera
The Sirius Scheimpflug-Camera gives values of both the
nasal and the temporal ACA in a single measurement.
The central fixation target of the device was used to align
the subject’s eye along the visual axis and to bring the
device into focus. The subject was instructed to blink and
open his/her eye widely before each measurement. Three
consecutive measurements were carried out per eye and a
mean value of the ACA was calculated which was taken
as the single measured value that was compared to the
values obtained by the other methods. Phoenix Software-
Suite was used by the device in this study to analyse the
obtained Scheimpflug images.
3.6. Angle Conversion
As stated before, both the AS-OCT and the Sirius
Scheimpflug-Camera measure the ACA in degrees and
can therefore not be directly compared to the van Herick
technique and gonioscopy. Hence the ACA values ob-
tained with these two devices were converted to the van
Herick’s grading system using Shaffer’s anterior cham-
ber angle grading system (illustrated in Table 2). Never-
theless, both AS-OCT and the Sirius Scheimpflug-
Camera measure the ACA in degrees so comparisons
between them were performed in degrees.
3.7. Statistical Analysis
The Graph pad Instat for windows (Version 3.10) was
used for statistical analysis. The Friedman test with post-
test was used for comparison between two different me-
thods. The Wilcoxon matched pair test was used for ei-
ther nasal or temporal data comparison between two me-
thods. A p value less than 0.05 (p < 0.05) was considered
statistically significant and indicated a difference be-
tween the measurements.
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Evaluation of Nasal and Temporal Anterior Chamber Angle with Four Different Techniques 551
4. Results
The descriptive statistics for nasal and temporal measure-
ments is shown in Table 3.
The mean ACA measured by gonioscopy and the van
Herick technique differed by 0.12 nasally and by 0.04
temporally. No statistically significant difference could
be found between these two methods (p = 0.45) either
nasally (p = 0.20) or temporally (p = 0.68). Figure 1
compares measurements obtained by gonioscopy to that
obtained by van Herick technique.
On comparison of the mean ACA values obtained by
gonioscopy to that obtained by the AS-OCT a difference
of 0.14 was observed nasally and a difference of 0.08
was observed temporally. But no statistically significant
difference could be found between the two methods (p =
0.09) neither nasally (p = 0.15) nor temporally (p = 0.36).
A comparison of AS-OCT findings to that of gonioscopy
is shown in Figure 2.
When the mean ACA value obtained by gonioscopy is
compared to that obtained by the Sirius Scheimpflug-
Camera a difference of 0.18 was seen between nasal val-
ues and a difference of 0.30 was seen between temporal
11132132
6244
31
6
33
0
10
20
30
40
GN2GN3GN4GT2GT3 GT4
Number of eyes
VH1 VH2 VH3 VH4
Figure 2. Compares the measured ACA grading’s obtained
by gonioscopy to that obtained by van Herick technique.
Numbers over the bars; show the number of eyes, GN2 (go-
nioscopy nasal grade 2), GN3 (gonioscopy nasal grade 3),
GN4 (gonioscopy nasal grade 4), GT2 (gonioscopy temporal
grade 2), GT3 (gonioscopy temporal grade 3), GT4 (gonio-
scopy temporal grade 4), VH1, 2, 3 and 4 (van Herick grade
1, 2, 3 and 4).
Table 3. Descriptive statistics for nasal and temporal meas-
urements.
Gonio-scopy van Herick AS-OCT* Sirius**
Mean 3.66/3.66 3.54/3.62 3.52/3.58 3.84/3.96
SD*** 0.56/0.56 0.79/0.78 0.50/0.50 0.37/0.20
95%
confidence
interval
0.159/0.159 0.224/0.222 0.144/0.142 0.105/0.056
Range 2 - 4 1 - 4 3 - 4 3 - 4
*Anterior segment optical coherence tomography. **Sirius scheimpflug-
Camera. ***Standard deviation.
values. A statistically significant difference was found
between these two methods (p < 0.0001) both nasally (p
= 0.03) and temporally (p = 0.0002). Values obtained by
Sirius Scheimpflug-Camera are compared to that ob-
tained by gonioscopy in Figure 3.
A difference of 0.02 between the mean nasal meas-
urements and a difference of 0.04 between the mean
temporal measurements of the van Herick technique and
the AS-OCT was found. No statistically significant dif-
ference was found to exist between the two methods (p =
0.39) either nasally (p = 0.86) or temporally (p = 0.71).
Figure 4 shows a comparison of these two methods.
The mean ACA value obtained nasally by the van
Herick technique and the Sirius Scheimpflug-Camera
differed by 0.30 whilst that obtained temporally differed
by 0.34. The two methods were found to be significantly
different from each other (p < 0.0001) both nasally (p =
0.001) and temporally (p = 0.001). A comparison be-
tween these two methods.
The mean ACA value obtained nasally by the van
22
10
3
10
3
12
23
9
26
0
5
10
15
20
25
30
AS-OCTN3AS-OCTN4 AS-OCTT3AS-OCTT4
Number of eyes
G2 G3 G4
Figure 3. Compares the measured ACA grading’s obtained
by AS-OCT to that obtained by gonioscopy. Numbers over
the bars, show the number of eyes AS-OCTN3 (AS-OCT
nasal grade 3) AS-OCTN4 (AS-OCT nasal grade 4) AS-
OCTT3 (AS-OCT temporal grade 3) AS-OCTT4 (AS-OCT
temporal grade 4) G2, 3 and 4 (gonioscopy grade 2, 3 and 4).
11 2
582
11
2
33 35
0
10
20
30
SN3 SN4 ST3ST4
Number of eyes
G2 G3 G4
Figure 4. Compares the measured ACA grading obtained by
Sirius Scheimpflug-Camera to that obtained-by gonioscopy.
Numbers over the bars, show the number of eyesSN3 (Sirius
Scheimpflug-Camera nasal grade 3) SN4 (Sirius Scheimp-
flug-Camera nasal grade 4) ST3 (Sirius Scheimpflug-Cam-
era temporal grade 3) ST4 (Sirius Scheimpflug-Camera tem-
poral grade 4.
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Evaluation of Nasal and Temporal Anterior Chamber Angle with Four Different Techniques
552
Herick technique and the Sirius Scheimpflug-Camera
differed by 0.30 whilst that obtained temporally differed
by 0.34. The two methods were found to be significantly
different from each other (p < 0.0001) both nasally (p =
0.001) and temporally (p = 0.001). A comparison be-
tween these two methods is illustrated in Figure 5.
Table 4 shows the descriptive statistic in degrees for
nasal and temporal measurements obtained by the AS-
OCT and the Sirius Scheimpflug-Camera. When com-
paring the mean ACA value obtained by the AS-OCT to
that obtained by the Sirius Scheimpflug-Camera a dif-
ference of 7.840 was observed nasally and a difference of
10.880 was observed temporally. Thus a statistically sig-
nificant difference was found to exist between these two
methods (p < 0.0001) both nasally (p < 0.0001) and tem-
porally (p < 0.0001). Values obtained by these two
methods are compared to each other in Figure 6.
5. Discussion
To decrease the risk for irreversible blindness due to
ACG, a quick and easy ACA evaluation method is
needed that should be a part of the routine eye examina-
tion.
11
66
84
9
26
10
29
0
10
20
30
AS-
OCTN3 AS - OCTN4 AS - OCTT3 AS- OCTT4
Number o f eyes
VH1 VH2 VH3 VH4
Figure 5. Compares the measured ACA grading’s obtained
by the AS-OCT to that obtained by van Herick technique.
Numbers on the bars, show the number of eyes. AS-OCTN3
(AS-OCT nasal grade 3) AS-OCTN 4 (AS-OCT nasal grade
4) AS-OCTT3 (AS-OCT temporal grade 3) AS-OCTT4
(AS-OCT temporal grade 4) VH1, 2, 3 and 4 (van Herick
grade 1, 2, 3 and 4).
Table 4. ACA measurement in degrees obtained by AS-
OCT and the Sirius Scheimpflug-came r a.
AS-OCT*
nasal
(in degrees)
Sirius**
nasal
(in degrees)
AS-OCT*
temporal
(in degrees)
Sirius** temporal
(in degrees)
Mean 35.86 43.70 37.66 48.53
SD*** 7.059 5.819 5.793 7.042
95%
confidence
interval
1.66 2.01 2.00 1.64
Range 26 - 49.2 30 - 61.67 27 - 53.3 34 - 65
11
3324444
35 39
0
10
20
30
40
SN3 SN4ST3ST4
Number of eyes
VH1 VH2VH3 VH4
Figure 6. Compares the measured ACA grading’s obtained
by Sirius Scheimpflug-Camera to that obtained by van
Herick technique. Numbers on the bars, show the number of
eyes. SN3 (Sirius Scheimpflug-Camera nasal grade 3) SN4
(Sirius Scheimpflug-Camera nasal grade 4) ST3 (Sirius Sch-
eimpflug-Camera temporal grade 3) ST4 (Sirius Scheimp-
flug-Camera temporal grade 4) VH1, 2, 3 and 4 (van Herick
grade 1, 2, 3 and 4).
The van Herick technique, AS-OCT and Sirius Sch-
eimpflug-Camera can be used for this purpose as they all
are quick and easy to perform. But we need to know
which one of these is the most accurate one to be used.
To answer this question they have to be compared to
gonioscopy which is the current reference standard for
ACA measurement. This study was therefore carried out
to investigate variation between these four different
methods in measuring the ACA.
Our study showed good agreement between gonio-
scopy and the van Herick technique since no statistically
significant difference could be found between the two
methods (p = 0.45) either nasally (p = 0.20) or tempo-
rally (p = 0.68). Best agreement was shown for angles
that had grade 4 since the majority of the eyes graded as
4 by gonioscopy were also graded as 4 by van Herick
technique both nasally and temporally (Figure 1). This
finding is in good agreement with the results of the study
by Foster et al. where they also show good agreement
between gonioscopy and van Herick technique especially
for eyes having grade 4 [15].
Good agreement between gonioscopy and van Herick
technique is also reported in a study by Park et al. and in
another study by Kashiwagi et al. and in one other study
by Foster et al. [3,15,16]. However, the result of our
study disagrees with that of the study by Thomas et al.
where poor agreement between gonioscopy and van
Herick technique is reported. Difference in the study
population between the two studies may explain this
disagreement. Most of the subjects enrolled in their study
had narrow angles whilst most of the subjects enrolled in
our study had normal angles.
Both gonioscopy and the van Herick technique make
use of the slit lamp to measure the ACA and both are
subjective methods. These similarities can be the reason
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Evaluation of Nasal and Temporal Anterior Chamber Angle with Four Different Techniques 553
for good agreement between the two methods.
Our findings suggest poor agreement between gonio-
scopy and the Sirius Scheimpflug-Camera (p < 0.0001)
both nasally (p = 0.03) and temporally (p = 0.0002). No
studies comparing Sirius Scheimpflug-Camera to gonio-
scopy has been performed before. Though, in a study by
Friedman et al., the ACA measured by Scheimpflug
camera is compared to the measurements obtained by
gonioscopy and poor agreement between the two is re-
ported [23].
Statistically significant difference between the results
obtained by the Sirius Scheimpflug-Camera and the van
Herick technique exists according to this study, indicat-
ing poor agreement between the two methods (p <
0.0001) both nasally (p = 0.001) and temporally (p =
0.001).
Sirius Scheimpflug-Camera is in disagreement with
gonioscopy and the van Herick technique may be be-
cause of its different nature compared to the other two
methods. Both gonioscopy and the van Herick technique
are subjective methods whilst the Sirius Scheimpflug-
Camera gives an objective measurement of the ACA. As
stated before, both gonioscopy and the van Herick tech-
nique make use of the slit lamp whilst the Sirius Sch-
eimpflug-Camera uses the 3D rotating Scheimpflug ca-
mera and bases its measurement results on the pictures
obtained by that camera. In addition, the illumination
used by the topographic rings and the fixation target of
the Sirius Scheimpflug-Camera is a bit bright. This
brightness can cause pupil constriction, which increases
the angle width and there by a wider angle measure is
given.
This study also showed good agreement between the
results obtained by gonioscopy and the AS-OCT (p =
0.09) for both nasal (p = 0.15) and temporal data (p =
0.36). In a study by Sakata et al. poor agreement between
gonioscopy and AS-OCT is reported for superior and
inferior angles, but the agreement for nasal and temporal
angle is reported to be good [18]. They also stated that
AS-OCT tends to detect more closed ACAs than gonio-
scopy which can partly be seen in our study too. When
comparing the mean ACA values obtained by gonio-
scopy to that obtained by AS-OCT, it can be seen that
AS-OCT measures the angle 0.14 nasally and 0.08 tem-
porally narrower than gonioscopy.
Our study showed good agreement between the AS-
OCT and the van Herick technique (p = 0.39) both na-
sally (p = 0.86) and temporally (p = 0.71). However,
AS-OCT is reported to be in disagreement with gonio-
scopy and van Herick technique in a study by Park et al.
[3]. Eyes with narrow angles were used in their study
whilst eyes with normal angles were used in our study.
This difference in the selection of eyes in the two studies
might be the reason for the disagreement between them.
AS-OCT also measures the ACA objectively but
unlike Sirius Scheimpflug-Camera, it is in good agree-
ment with both gonioscopy and the van Herick technique.
This can partly be explained by the fact that both gonio-
scopy and the AS-OCT make a direct view of the ACA
configuration to measure it. Also the AS-OCT makes use
of an internal fixation target of low illumination to com-
pensate for the subject’s refractive error as well as pre-
vent pupil constriction. Compensation of the refractive
error is essential for prevention of the pupil constriction
and lens disposition which normally occurs as a result of
accommodation [24].
According to this study the results obtained by the
AS-OCT differ significantly from those obtained by the
Sirius Scheimpflug-Camera (p < 0.0001) both nasally (p
< 0.0001) and temporally (p < 0.0001) showing dis-
agreement between the two devices.
The Sirius Scheimpflug-Camera makes use of visible
light to measure the angle and can thus alter the angle
configuration whilst the AS-OCT makes use of infrared
light for its angle measurement. Besides, the Sirius
Scheimpflug-Camera does not make any adjustment for
the subject’s refractive error and makes use of quite
bright illumination in its fixation target and in its topog-
raphic rings. The AS-OCT on the other hand takes all of
these factors in to account, which may thus explain the
existence of poor agreement between the two devices.
To state which one of the three methods (i.e. van
Herick technique, AS-OCT and Sirius Scheimpflug-
Camera) is the most accurate one to be used, is difficult
because all of these methods have their own strengths
and weaknesses. For instance, although the van Herick
technique is a quick method that makes use of a slit lamp
(which is available to all the optometrists and does not
cost very much), it requires experience and good meas-
uring skill to get reliable measurements [1]. Furthermore,
it is a subjective method that gives an estimation of the
angle as well as affected by the corneal thickness [4].
In contrast, measuring the ACA with the AS-OCT and
Sirius Scheimpflug-Camera is not only quick but also
easy to perform. In addition, they do not require much of
experience and measuring skill and are objective meth-
ods. Nevertheless, the weakness of these devices is their
high cost.
This study did have limitations. The illumination of
the room which plays a vital role on the pupil constric-
tion and dilation was not controlled in this study. At
times the ACA was measured in a totally dark room and
at times it was measured in a dimly illuminated room.
This should, however, not affect the results enormously
since light falling directly on the pupil affects its size
more than the room illumination. And the light directly
falling on the pupil was from the illumination used by the
slit lamp and the fixation target used by the Sirius
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Evaluation of Nasal and Temporal Anterior Chamber Angle with Four Different Techniques
554
Scheimpflug-Camera and the AS-OCT. The measure-
ments by gonioscopy and the van Herick technique were
carried out by the same examiner which might have pro-
duced systemic bias. The number of subjects used in this
study was not very big, so in order to get more reliable
results the study should be performed on a larger group
of people. In spite of these limitations, this study to the
best of our knowledge is the first one to compare the
Sirius Scheimpflug-Camera with gonioscopy, the van
Herick technique and the AS-OCT.
6. Conclusion
In summary, this study showed good agreement between
gonioscopy, the van Herick technique and the AS-OCT.
The agreement between the Sirius Scheimpflug-Camera
and the other three methods (i.e. gonioscopy, van Herick
technique and AS-OCT) on the other hand was poor. It
should therefore be noted that the ACA measurements
obtained by the Sirius Scheimpflug-Camera, which can-
not be considered interchangeable with those obtained by
gonioscopy, the van Herick technique and the AS-OCT.
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