Detection of occludable angles with the Pentacam and the anterior segment optical coherence tomography.

Abstract

To assess efficacy of the Pentacam (PTC) and the anterior segment optical coherence tomography (AOCT) for detection of occludable angles.
Fourty-one eyes with gonioscopically diagnosed occludable angles and 32 normal open-angle eyes were included. Anterior chamber angle (ACA) and anterior chamber depth (ACD) were measured with PTC and AOCT. Receiver operating characteristic (ROC) curve was constructed for each parameter and the area under the ROC curve (AUC) was calculated.
Values of ACA and ACD measured by PTC and AOCT were similar not only in normal open angle eyes but also in occludable angle eyes. For detection of occludable angle, the AUCs of PTC with ACA and ACD were 0.935 and 0.969, respectively. The AUCs of AOCT with ACA and ACD were 0.904 and 0.947, respectively.
Both PTC and AOCT allow accurate discrimination between open and occludable angle eyes, so that they may aid to screening the occludable angles.

Full text

Page 1

Yonsei Med J http://www.eymj.org Volume 50 Number 4 August 2009
525
Primary angle closure glaucoma (PACG) is known to be highly prevalent among
some ethnic groups, especially those of Mongolian descent.1-5Foster and Johnson2
have estimated that 1.7 million people in China are bilaterally blind from glaucoma
and 91% of them are attributable to PACG. The number of people with a
predisposing risk of anatomically occludable angles is estimated to be 28.2 million,
and 9.1 million with significantly closed angle.3For several decades, it is believed
that proper prophylactic laser peripheral iridotomy prevents occludable angles
from the angle closure attack.6,7As damage by acute angle closure is irreversible;
screening for occludable angles in endemic areas of angle closure is important.
PACG is diagnosed in cases that have an occludable angles combined with
glaucomatous optic neuropathy and consistent visual field defect. Gonioscopy is
the gold standard for identifying occludable angles, but it requires expertise of a
highly skilled examiner. In addition, it is a relatively subjective technique, and
intra- and inter-observer reproducibility is poor. There are no uniform gonioscopic
criteria to identify angles that require treatment.8,9
The Pentacam (PTC, Oculus Inc., Wetzlar, Germany) and the anterior segment
optical coherence tomography (AOCT; SL-OCTTM, Heidelberg Engineering,
GmbH, Germany) can provide more rapid and quantitative images compared to
the conventional gonioscopy. Their cross-sectional images of the anterior chamber
angle (ACA) and anterior chamber depth (ACD) may be used to screen for
occludable angles.
Original Article
DOI 10.3349/ymj.2009.50.4.525
pISSN: 0513-5796, eISSN: 1976-2437
Yonsei Med J 50(4): 525-528, 2009
Detection of Occludable Angles with the Pentacam and
the Anterior Segment Optical Coherence Tomography
Samin Hong,* Jeong-Ho Yi,* Sung Yong Kang, Gong Je Seong, and Chan Yun Kim
Institute of Vision Research, Department of Ophthalmology, Yonsei University College of Medicine, Seoul, Korea.
Purpose: To assess efficacy of the Pentacam (PTC) and the anterior segment optical coherence tomography
(AOCT) for detection of occludable angles. Materials and Methods: Fourty-one eyes with gonioscopically
diagnosed occludable angles and 32 normal open-angle eyes were included. Anterior chamber angle (ACA) and
anterior chamber depth (ACD) were measured with PTC and AOCT. Receiver operating characteristic (ROC)
curve was constructed for each parameter and the area under the ROC curve (AUC) was calculated. Results:
Values of ACA and ACD measured by PTC and AOCT were similar not only in normal open angle eyes but also
in occludable angle eyes. For detection of occludable angle, the AUCs of PTC with ACA and ACD were 0.935 and
0.969, respectively. The AUCs of AOCT with ACA and ACD were 0.904 and 0.947, respectively. Conclusion:
Both PTC and AOCT allow accurate discrimination between open and occludable angle eyes, so that they may aid
to screening the occludable angles.
Key Words :Pentacam, anterior segment optical coherence tomography, occludable angle, anterior chamber angle,
anterior chamber depth
Received: September 22, 2008
Revised: December 9, 2008
Accepted: December 9, 2008
Corresponding author: Dr. Chan Yun Kim,
Department of Ophthalmology,
Yonsei University College of Medicine,
250 Seongsan-ro, Seodaemun-gu,
Seoul 120-752, Korea.
Tel: 82-2-2228-3580, Fax: 82-2-312-0541
E-mail: kcyeye@yuhs.ac
*They equally contributed to this work.
∙Presented: 8th European Glaucoma Society
Congress, June 1-6, 2008, Berlin, Germany.
∙The authors have no financial conflicts of
interest.
© Copyright:
Yonsei University College of Medicine 2009
INTRODUCTION

Page 2

Samin Hong, et al.
Yonsei Med J http://www.eymj.org Volume 50 Number 4 August 2009
526
In the present study, we evaluated the efficacy of PTC
and AOCT as a screening tool for the detection of occlu-
dable angles.
After obtaining approval of the Institutional Review Board,
seventy-three participants were enrolled in this study.
Informed consent was obtained from each subject. Subjects
with any history of previous ocular trauma or intraocular
disease/surgery were excluded. One eye in each subject
was randomly chosen for the analysis. Occludable angle
was defined when the trabecular meshwork was seen in
less than 90 degrees of the angle circumference by gonios-
copy without indentation.10
For each subject, ACA and ACD were measured by the
PTC and AOCT, respectively, under the uniform dim illu-
mination. Angle images were captured using the horizontal
linear scan protocol (from 3-o’clock to 9-o’clock direction)
because images of the temporal and nasal angles, can be
taken more easily than those of superior and inferior angles
and they need no eyelid manipulation to expose the lim-
bus.11ACA was measured automatically by PTC and AOCT
[angle at the angle recess area at 500 µm (ARA 500)].12
ACD was defined as the distance from the posterior vertex
of the corneal endothelium to the anterior surface of the
crystalline lens along the optical axis. All measurements
were repeated twice by single investigator, and an average
of 2 measurements was used to further analyses.
The receiver operating characteristic (ROC) curve was
constructed for each parameter, and the area under the
ROC curve (AUC) was calculated to compare the discri-
minating ability of each parameter of each instrument.
Statistical analyses other than ROC curves were carried
out using SPSS for Windows, version 11.0 (SPSS Inc,
Chicago, Il, USA), and statistical analysis for the ROC
curves was performed using Medcalc for Windows,
version 7.6.0.0 (Medcalc Software, Mariakerke, Belgium).
Among all 73 eyes, 41 eyes had an occludable angle and
32 eyes showed normal open angle by gonioscopy without
indentation. Mean ages for occludable angle patients and
MATERIALS AND METHODS
RESULTS
Table 1. Anterior Chamber Angle and Anterior Chamber Depth by Pentacam and Anterior Segment Optical
Coherent Tomography in Occludable Angle and Open Angle Subjects
PTC
ACA (degrees)
All eyes30.21 ±8.94
Open angle eyes 37.72 ±6.71
Occludable angle eyes24.35 ±5.35
p value< 0.001
ACD (mm)
All eyes2.26 ±0.61
Open angle eyes2.83 ±0.46
Occludable angle eyes1.86 ±0.30
p value < 0.001
ACA, anterior chamber angle; ACD, anterior chamber depth; AOCT, anterior segment optical coherent tomography; PTC, pentacam.
Values given as means±standard deviation.
*Student t-test between PTC and AOCT.
�Student t-test between open angle and occludable angle eyes.
AOCT
p value*
27.33 ±9.97
35.26 ±8.34
21.15 ±5.97
< 0.001
0.070
0.200
0.012
-
�
2.36 ±0.58
2.88 ±0.34
1.95 ±0.36
< 0.001
0.300
0.630
0.180
-
�
Table 2. Cut-Off Points of the Receiver Operating Characteristic Curves to Discriminate Occludable Angles
and Open Angles
Cut-off value
Anterior chamber angle
PTC 29.5 degrees
AOCT31.8 degrees
Anterior chamber depth
PTC 2.27 mm
AOCT 2.45 mm
AOCT, anterior segment optical coherent tomography; PTC, pentacam.
Sensitivity (%) Specificity (%)
87.5
75.0
90.2
97.6
92.9
87.5
95.0
97.6

Page 3

normal controls were 67.5 ± 8.0 years (range, 54 to 81
years) and 62.2 ± 11.5 years (range, 48 to 84 years),
respectively (p = 0.024). Thirteen (31.7%) patients in the
occludable angle group and 10 (31.3%) patients in the
control group were men.
ACA and ACD data obtained by PTC and AOCT are
shown in Table 1. Values of ACA measured by PTC and
AOCT were similar within each of the two populations
(occludable angles; p = 0.012, open angles; p = 0.200).
ACD measured by PTC and AOCT showed also similar
results in both study groups (occludable angles; p = 0.180,
open angles; p = 0.630).
Fig. 1 shows the ROC curves of ACA and ACD,
measured by PTC and AOCT. The AUCs of PTC with
ACA and ACD were 0.935 (cut-off, 29.5 degrees) and
0.969 (cut-off, 2.27 mm), respectively. The AUCs of AOCT
with ACA and ACD were 0.904 (cut-off, 31.8 degrees)
and 0.947 (cut-off, 2.45 mm), respectively. Data at these
cut-off points are listed in Table 2. With fixed sensitivity of
80.0%, the PTC showed 92.7% (ACA) and 100% (ACD)
specificity, and the AOCT showed 85.4% (ACA) and
97.6% (ACD) specificity.
In the present study, anterior chamber images were taken
by PTC and AOCT to evaluate their discriminating ability
to detect an occludable angle. These two instruments had
large AUCs for both ACA and ACD. Especially, ACD by
PTC had the largest AUC (0.969), so that ACD measure-
ment by PTC might have the most powerful discriminating
ability for the occludable angle detection.
Even though the conventional gonioscopy has been used
as a standard method to examine the angle structure, it has
several weak points. It requires expertise of a highly skilled
Occludable Angles with Pentacam and AS OCT
Yonsei Med J http://www.eymj.org Volume 50 Number 4 August 2009
527
DISCUSSION
0
20
40
60
80
100
02040
100-specificity
60
Sensitivity
80 100
0
20
40
60
80
100
02040
100-specificity
60
Sensitivity
80100
0
20
40
60
80
100
0 2040
100-specificity
60
Sensitivity
80100
0
20
40
60
80
100
02040
100-specificity
60
Sensitivity
80100
Fig. 1.Receiver operating characteristic curves. (A) Anterior chamber angle by Pentacam. (B) Anterior chamber angle by Anterior segment optical
coherent tomography. (C) Anterior chamber depth by Pentacam. (D) Anterior chamber depth by anterior segment optical coherent tomography.
AB
CD

Page 4

Samin Hong, et al.
Yonsei Med J http://www.eymj.org Volume 50 Number 4 August 2009
528
examiner, and it uses a relatively subjective classification
of angle structure. For these reasons, there have been several
attempts to develop new imaging techniques. Redhakri-
shnan, et al.6,7reported that there was no significant
difference between OCT and ultrasound biomicroscopic
parameters of anterior chamber angles. Nolan, et al.13
examined ACA by gonioscopy as well as AOCT. Winifred
and associates evaluated sensitivity of OCT in detecting
angle closure compared with gonioscopy.14Using gonios-
copy as reference standard, results in AOCT showed a
sensitivity of 81.5% and a specificity of 68.5% in the nasal
quadrant; 66.1% and 77.2% in the temporal area. How-
ever, it was a qualitative comparison of anterior chamber
angles. In the present study, these two instruments (AOCT
and PTC) showed good results. Therefore, not only AOCT
but also PTC may be excellent candidates for screening of
occludable angles.
As for inter-device agreement and cut-off value distin-
guishing occludable angle, ACD was better than ACA
using both PTC and AOCT. And, even though statistically
not significant, ACA in occludable angle patients showed
slight differences between PTC and AOCT (p = 0.012).
There are some possible explanations for these findings. It
is possible that the contact gonioscopy lens for conven-
tional gonioscopy, when placed on the globe, causes some
displacement of anterior segment structures, while the use
of Zeiss-type gonioscopic lens causes no pressure on the eye,
resulting in opening of the angles. Furthermore, although
gonioscopy, PTC, and AOCT examinations are underta-
ken under dim lighting conditions, the intensity of light
illuminated during each examinations is different from
each other. This is inevitable for both the production of
Scheimpflug images in PTC and the slit beam in case of
gonioscopy. Light of varying intensity can open the angle
to a different degree, especially in patients with an occlu-
dable angle. Ultrasound biomicroscopic studies demonst-
rate the dramatic changes in angle width that take place
when going from dark to light.15However, unlike ACA;
ACD is less influenced by light. This suggests that the
difference in light intensity used during each examination
could be an important factor for the difference in range of
agreement between ACA and ACD.
In conclusion, we have shown that the quantitative angle
parameters and anterior chamber depths, as measured by
PTC, have similar mean values, reproducibility, and sensi-
tivity-specificity profiles when compared with measure-
ments obtained by AOCT. In this limited data set, these
parameters showed discriminative cut-off value in the scre-
ening of occludable angles. The ease of image acquisition
and the non-contact nature of PTC and AOCT are highly
desirable. ACA and ACD using both modalities could
have a novel potential application for screening of eyes with
occludable instead of gonioscopic examination. Further
study with a larger sample size is required to clearly define
the utility of PTC and AOCT parameters (ACA, ACD) in
screening of occludable angle and angle-closure glaucoma.
1. Bonomi L, Marchini G, Marraffa M, Bernardi P, De Franco I,
Perfetti S, et al. Epidemiology of angle-closure glaucoma: preva-
lence, clinical types, and association with peripheral anterior
chamber depth in the Egna-Neumarket Glaucoma Study. Oph-
thalmology 2000;107:998-1003.
2. Foster PJ, Johnson GJ. Glaucoma in China: how big is the pro-
blem? Br J Ophthalmol 2001;85:1277-82.
3. Alsbirk PH. Anterior chamber depth and primary angle-closure
glaucoma. I. An epidemiologic study in Greenland Eskimos. Acta
Ophthalmol (Copenh) 1975;53:89-104.
4. Chew PT, Aung T. Primary angle-closure glaucoma in Asia. J
Glaucoma 2001;10:S7-8.
5. Dandona L, Dandona R, Mandal P, Srinivas M, John RK, McCarty
CA, et al. Angle-closure glaucoma in an urban population in
southern India. The Andhra Pradesh eye disease study. Ophthal-
mology 2000;107:1710-6.
6. Radhakrishnan S, Goldsmith J, Huang D, Westphal V, Dueker
DK, Rollins AM, et al. Comparison of optical coherence tomo-
graphy and ultrasound biomicroscopy for detection of narrow
anterior chamber angles. Arch Ophthalmol 2005;123;1053-9.
7. Radhakrishnan S, Huang D, Smith SD. Optical coherence tomo-
graphy imaging of the anterior chamber angle. Ophthalmol Clin
North Am 2005;18:375-81, vi.
8. Foster PJ, Buhrmann R, Quigley HA, Johnson GJ. The definition
and classification of glaucoma in prevalence surveys. Br J Oph-
thalmol 2002;86:238-42.
9. Friedman DS. Who needs an iridotomy? Br J Ophthalmol 2001;
85:1019-21.
10. Foster PJ, Devereux JG, Alsbirk PH, Lee PS, Uranchimeg D,
Machin D, et al. Detection of gonioscopically occludable angles
and primary angle closure glaucoma by estimation of limbal
chamber depth in Asians: modified grading scheme. Br J Oph-
thalmol 2000;84:186-92.
11. Lackner B, Schmidinger G, Skorpik C. Validity and repeatability
of anterior chamber depth measurements with Pentacam and
Orbscan. Optom Vis Sci 2005;82:858-61.
12. Gazzard G, Foster PJ, Friedman DS, Khaw PT, Seah S. Light to
dark physiological variation in irido-trabecular angle width. Br J
Ophthalmol 2004;88:1357-482. Video report. http://bjo.
bmjjournals.com/cgi/content/full/88/11/DC1/1.
13. Nolan WP, See J, Aung T, Ce Z, Radhakrishnan S, Friedman DS,
et al. Detection of patients at risk of angle-closure using anterior
segment OCT. Invest Ophthalmol Vis Sci 2005;46:E-Abstract 145.
14. Nolan WP, See JL, Chew PT, Friedman DS, Smith SD, Radha-
krishnan S, et al. Detection of primary angle closure using anterior
segment optical coherence tomography in Asian eyes. Ophthal-
mology 2007;114:33-9.
15. Ishikawa H, Liebmann JM, Ritch R. Quantitative assessment of
the anterior segment using ultrasound biomicroscopy. Curr Opin
Ophthalmol 2000;11:133-9.
REFERENCES