Download Anterior chamber depth measurement

UPDATE/REVIEW
Anterior chamber depth measurement:
interchangeability between Pentacam and other devices
Alberto Domínguez-Vicent, MSc1; Daniel Monsálvez-Romín, OD1; Vicent Sanchis, MSc1;
Santiago García-Lázaro, OD, PhD1; Robert Montés-Micó, OD, PhD1.
ABSTRACT: We reviewed a series of recently published studies in which the anterior
chamber depth (ACD) distance was measured by Pentacam or Pentacam HR and compared
with other measuring devices. Since some published studies reach contradictory conclusions
regarding device interchangeability and include different ocular conditions, for instance,
phakic eyes, pseudophakic eyes, cataractous eye, and so on, this review was carried out to
try to clarify which clinical devices can or cannot be considered as interchangeable with
Pentacam or Pentacam HR for the measurement of ACD distance in clinical practice.
J Emmetropia 2012; 3: 215-220
Nowadays, the measurement of anterior chamber
depth (ACD) distance has become increasingly important
in ophthalmic practice, for instance, in the planning
of cataract1-5 and refractive1-9 surgery, calculation of
phakic or pseudophakic IOL power and diameter4,5,10-14,
screening for glaucoma risk factors2,3,14-16, and so on.
Many papers focusing on device interchangeability for
the measurement of ACD distance have been published.
However, the studies published include different ocular
conditions.
For this reason, we decided to review all studies
published in Medline before August 2012. The inclusion
criterion was that the study had to evaluate device
interchangeability between Pentacam or Pentacam
HR and other devices that measure ACD distance.
The devices included in this review were Pentacam
(Oculus, Wetzlar, Germany), Pentacam HR (Oculus,
Wetzlar, Germany), A-Scan, Ultrasound Biomicroscopy
(UBM), Orbscan (Bausch&Lomb Surgical Inc., San
Dimas, California, USA), Orbscan II (Bausch&Lomb
Surgical Inc., San Dimas, California, USA), Galilei
(Ziemer, Switzerland), Visante OCT (Carl Zeiss
Meditec Inc., Dublin, California, USA), IOLMaster
(Carl Zeiss Meditec, Jena, Germany) and Lenstar LS
900/Biograph (Haag-Streit AG, Koeniz, Switzerland/
Alcon Laboratories Inc., Ft Worth, Texas, USA). In
this context, the purpose of this paper was to clarify
which devices are interchangeable with Pentacam or
Pentacam HR in the measurement of ACD distances.
We also included a brief description of the measurement
principle used by the devices included in this review.
MEASUREMENT PRINCIPLES
1
Optometry Research Group (GIO), Department of Optics.
University of Valencia. Spain.
Financial disclosure: This research was supported in part by Research
Grant #SAF2009-13342-E# awarded by the Ministry of Science and
Innovation (Ministerio de Ciencia e Innovación) and by a BAF research
scholarship (Generalitat Valenciana) awarded to Alberto Domínguez
Vicent. The authors have no proprietary interest in any of the products
or devices mentioned in this article.
Corresponding Author: Alberto Domínguez Vicent.
Department of Optics - University of Valencia. C/ Dr. Moliner, 50
46100 - Burjassot. Spain. Phone: +34 963544764 - Fax: +34963544715
Email: [email protected]
© 2010 SECOIR
Sociedad Española de Cirugía Ocular Implanto-Refractiva
Pentacam
The Pentacam is a non-contact device using a
rotating Scheimpflug camera. It uses a monochromatic
slit light source to measure anterior segment topography.
Up to 50 slit images with 500 measurement points on
the front and back of the corneal surface are acquired
in 2 seconds over a 180-degree rotation. The internal
software creates a three-dimensional reconstruction of
the anterior segment by using the elevation data of these
images, which gives information about the anterior
and posterior surface of the cornea, and ACD from
endothelium to crystalline lens.
ISSN: 2171-4703
215
216
COMPARISON OF ANTERIOR CHAMBER DEPTH MEASUREMENT DEVICES
Figure 1. Pentacam HR (left) and Galilei (right).
Figure 2. Orbscan II (left) and Visante OCT (right).
Pentacam HR
Pentacam HR (Figure 1 left) is one of the latest
developments in three-dimensional topographers and is
based on the Scheimpflug principle. The rotating camera
rotates around the optical axes of the eye to calculate a
three-dimensional model of the anterior segment. The
system has two different three-dimensional modes. One
is a regular three-dimensional scan that takes 50 images
in 2 seconds. The other is a special three-dimensional
high-resolution corneal mode, in which the camera
takes 50 images per second. The internal software creates
a three-dimensional reconstruction of the anterior
segment by using the elevation data of these images,
giving information about the anterior and posterior
surface of the cornea, and ACD from endothelium to
crystalline lens.
different techniques: a Placido disk system, which screens
anterior corneal topography and creates an elevation
map; and a horizontally moving scanning camera,
which acquires slit images. After image reconstruction,
a mathematical three-dimensional model of the cornea
and the anterior segment is calculated. To calculate the
ACD, the system software automatically detects the
corneal endothelium surface and anterior surface of the
crystalline lens on the acquired images.
A-Scan
This ultrasound contact device, which works at
10-MHz, is used to measure eye biometric dimensions,
i.e. axial length, anterior chamber depth, posterior
chamber depth and corneal and lens thickness. It
calculates ACD on the basis of the difference in the
time taken for ultrasound waves to reflect back to its
receiver from the posterior corneal surface and anterior
lens surface.
Ultrasound Biomicroscopy
This ultrasound contact device, which works at 50
MHz, is used to image ocular tissue depths up to 4
to 5 mm with lateral and axial physical resolution of
approximately 50 and 25 µm. ACD is measured with a
ruler over the sonogram.
Orbscan
The Orbscan is a noncontact topography system
that is used for anterior segment evaluation. It uses two
Orbscan II
The Orbscan II (Figure 2 left) is a non-invasive
topography system that scans the anterior segment,
combining a three-dimensional scanning slit beam
system with an added Placido attachment for evaluating
corneal surfaces. This device calculates ACD in the same
manner as Orbscan.
Galilei
The Galilei (Figure 1 right) is a non-invasive
diagnostic system designed for the analysis of the
anterior eye segment. The system is based on a rotating
dual-Scheimpflug camera integrated with a Placido
topographer. This device captures slit images from
opposite sides of the illuminated slit and averages the
elevation data obtained from corresponding opposite
slit images. This dual Scheimpflug imaging technique
improves the detection of the posterior corneal surface
and provides outstanding accuracy in pachymetry across
the entire cornea, even when the camera is decentered
because of eye movements.
Visante OCT
Visante OCT (Figure 2 right) is a time-domain
non-invasive system that employs high-resolution
images. The light source is a superluminescent
light-emitting diode with a short wavelength that has
JOURNAL OF EMMETROPIA - VOL 3, OCTOBER-DECEMBER
COMPARISON OF ANTERIOR CHAMBER DEPTH MEASUREMENT DEVICES
217
Pentacam vs. A-Scan
Németh et al.7, Elbaz et al.17 and Su et al.18 studied
the interchangeability of Pentacam and A-Scan. These
authors included normal eyes in their sample but reached
different conclusions: while Németh et al.7 obtained
comparable ACD values, Elbaz et al.17 and Su et al.18
obtained significantly lower ACD values with A-Scan.
However, in these two latter studies the mean difference
lay within clinical tolerance limits. Németh et al.7 and Su
et al.18 also included pseudophakic eyes in their sample
and in these cases the ACD values provided by A-Scan
and Pentacam were not comparable. Therefore, it can
be concluded that A-Scan and Pentacam can be used
interchangeably in clinical practice for phakic subjects,
but not for pseudophakic eyes.
Figure 3. Lenstar (left) and IOLMaster (right).
a limited penetration depth into the eye. By moving
the scanning spot laterally across the eye, this device
acquires multiple A-Scans and aligns them to construct
two-dimensional images analogous to an ultrasound
B-scan. The scanning speed is 4,000 axial scans/second
and each image frame has 500 axial scans/image. It can
be used to measure central corneal thickness and ACD.
IOLMaster
The IOLMaster (Figure 3 right) is designed to
measure the parameters used in intraocular lens (IOL)
calculation, including axial length, corneal curvature,
ACD and WTW distance. The IOLMaster emits
780-nm infrared light and uses partial coherence
interferometry to measure axial length. Keratometry
and ACD are determined automatically using a lateral
slit illumination of the corneal and crystalline lens and
a white-light-emitting diode of 590 nm as the light
source. The lateral slit illumination is 0.7 mm wide
and employed at an angle of 30 degrees during ACD
measurements.
Lenstar
The Lenstar (Figure 3 left) optical biometer is based
on low coherence reflectometry, with an 820-mm
superluminescent diode. The Lenstar detects anterior
and posterior corneal and anterior crystalline lens peaks
in the optical low coherence reflectometry waveform to
measure the ACD and corneal thickness. In addition to
ACD and corneal thickness, the Lenstar also measures
axial length.
ANTERIOR CHAMBER DEPTH
Each study included in this study compared
Pentacam or Pentacam HR with one of the following
devices: A-Scan, UBM, Orbscan, Orbscan II, Galilei,
Visante OCT, IOLMaster, Lenstar and MRI.
Pentacam HR vs. A-Scan
Szalai et al.19 compared ACD measures provided by
Pentacam HR and A-Scan. They observed that A-Scan
yielded significantly higher ACD values than Pentacam
HR, thus concluding that these two devices cannot
be assumed to be interchangeable in clinical practice.
However, for IOL power calculation these devices can be
used interchangeably, since the mean difference between
these two devices is within clinical tolerance limits.
Pentacam vs. Orbscan
Lackner et al.12, Kiraly et al.20 and Yazici et al.21
compared Orbscan with Pentacam, but the results
they achieved were rather contradictor. Lackner et al.11
obtained significantly higher ACD values with Orbscan,
while in contrast, in the study of Yazici et al.21, it was
Orbscan that produced significantly lower ACD values.
However, the mean difference observed by Lackner et
al.11 and by Yazici et al.21 was within clinically acceptable
levels, which is why these two authors concluded that
these devices can be used interchangeably.
Pentacam vs. Orbscan II
Five studies8,15,16,23,24 evaluated the interchangeability
between Orbscan II and Pentacam. Doors et al.8, Dinc
et al.16, Hashemi et al.23 and Kim et al.24 obtained
statistically significant differences between the values
produced by these two devices, thus concluding
that they should not be used as though they were
interchangeable. In contrast, Utine et al.15 did not
observe any statistically significant differences between
Orbscan II and Pentacam, thus assuming their
interchangeability. It is worth mentioning that the mean
difference between Orbscan II and Pentacam was within
clinically acceptable tolerance limits in four8,15,16,24 out
of these five studies, which suggests that further studies
should be carried out to clarify whether or not these
two devices are interchangeable for the measurement of
ACD in normal eyes.
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COMPARISON OF ANTERIOR CHAMBER DEPTH MEASUREMENT DEVICES
Moreover, Doors et al.8 measured ACD in phakic eyes
following IOL implantation and Hashemi et al.23 and
Kim et al.24 following laser refractive surgery. While in all
three cases the authors observed statistically significant
differences between Orbscan II and Pentacam, the mean
difference was within clinically acceptance levels, except
for the Doors et al.8 study. Thus, we can conclude that
these are interchangeable after refractive surgery but not
after phakic IOL implantation.
Pentacam HR vs. Orbscan II
Salouti et al.22 compared Pentacam HR with Orbscan
II, obtaining significantly higher ACD values with
Orbscan II, thus concluding that these devices should
not be used interchangeably.
Pentacam vs. Galilei
Kiraly et al.20 compared the ACD values obtained
with Pentacam and Galilei. They did not find any
statistically significant differences between the two
devices, thus concluding that Pentacam and Galilei can
be employed interchangeably in clinical practice.
Pentacam vs. Visante OCT
Doors et al.8, Dinc et al.16, Kiraly et al.20, Yazici et
21
al. and O’Donnell et al.25 compared ACD measured
with Pentacam and with Visante OCT. No statistically
significant differences were found either by Kiraly et
al.20 or by Yazici et al.21, thus concluding that these
two devices can be used interchangeably in clinical
practice. On the contrary, Door et al.8, Dinc et al.16 and
O’Donnell et al.25 obtained significantly higher ACD
values with Visante OCT than with Pentacam, thus
concluding that these devices cannot be assumed to be
interchangeable. However, since the mean difference
obtained in these studies was within clinically acceptable
limits, we believe that Pentacam and Visante OCT can
be used interchangeably in normal eyes.
Doors et al.8 also included in their study a
comparison of patients that had undergone phakic IOL
implantation. In this group they also found statistically
significant differences but the mean difference was again
within clinical tolerance limits. Consequently, this study
suggests that Pentacam and Visante OCT can be also
used interchangeably to measure ACD in eyes that have
undergone phakic IOL implantation.
Pentacam vs. IOLMaster
Eight studies6,10,11,15-18,20 have so far compared
Pentacam with IOLMaster for the measurement of
ACD, all reaching similar conclusions. Savant et al.6,
Woodmass et al.10, and Kiraly et al.20 did not obtain any
statistically significant differences between Pentacam
and IOLMaster, and they concluded that these two
devices may be used interchangeably in clinical practice.
On the other hand, Reuland et al.11, Utine et al.15,
Dinc et al.16, Elbaz et al.17 and Su et al.18 observed
statistically significant differences between Pentacam
and IOLMaster, but they concluded that Pentacam and
IOLMaster can be considered as interchangeable for
use in clinical practice to calculate IOL power since the
mean difference between these two devices lay within
clinical tolerance levels. However, contradictory results
were found for the estimation of IOL vaulting: while
Reuland et al.11, Utine et al.15, Elbaz et al.17 and Su et
al.18 obtained mean differences within clinical tolerance
limits, Dinc et al.16 did not.
Moreover, Su et al.18 also compared Pentacam with
IOLMaster in pseudophakic subjects. Since the authors
did not obtain any statistically significant differences,
we may conclude that Pentacam and IOLMaster can be
used interchangeably for the measurement of ACD in
pseudophakic eyes.
Pentacam vs. Lenstar
Only two studies so far (O’Donnell et al.25 and
Huang et al.26) have compared Pentacam with Lenstar
for the measurement of ACD. Although O’Donnell et
al.25 found statistically significant differences between
these devices, as the mean difference was acceptable from
a clinical point of view, it was concluded that they were
interchangeable. However, Huang et al.26 did not find
statistically significant differences between Pentacam
and Lenstar. These studies, then, suggest that these two
devices can be used interchangeably in clinical practice.
Pentacam HR vs. Galilei
Salouti et al.22 also studied the interchangeability
between Pentacam HR and Galilei. They did not obtain
significantly differences and concluded that these
devices could be used interchangeably.
Pentacam HR vs. IOLMaster
Németh et al.27 studied the interchangeability
of Pentacam HR and IOLMaster in phakic eyes.
These authors did not find any statistically significant
differences between these two devices. This study, then,
suggests that Pentacam HR and IOLMaster can be used
interchangeably in the clinical practice.
DISCUSSION
After these reviews, it can be concluded that
the following devices can be used interchangeably
with Pentacam or Pentacam HR in clinical practice:
Pentacam-A-Scan7,17,18 for phakic patients, Pentacam
HR-A-Scan19 to calculate IOL power, PentacamOrbscan12,20,21 for phakic patients, Pentacam-Orbscan
II24 after laser refractive surgery, Pentacam-Galilei20 for
phakic patients, Pentacam-Visante OCT8,16,20,21,25 for
JOURNAL OF EMMETROPIA - VOL 3, OCTOBER-DECEMBER
COMPARISON OF ANTERIOR CHAMBER DEPTH MEASUREMENT DEVICES
phakic patients and after phakic IOL implantation,
Pentacam-IOLMaster6,10,11,15-18,20 to calculate IOL
power and after pseudophakic IOL implantation,
Pentacam-Lenstar25,26 for phakic patients, Pentacam
HR-Galilei22 for phakic patients and Pentacam
HR-IOLMaster26 for phakic patients.
The device pair whose interchangeability is still
unclear is Pentacam-Orbscan II8,15,16,20,23,24 for phakic
patients. Moreover, the device pairs that cannot be used
interchangeably in clinical practice are Pentacam-AScan7,18 for pseudophakic patients, Pentacam-Orbscan
II8 after phakic IOL implantation and Pentacam
HR-Orbscan II22 for healthy subjects.
The present review clarifies the interchangeability of
ACD measurements between Pentacam or Pentacam
HR and other devices. However, discrepancies between
studies may be due to the differences in the measurement
method upon which each device is based. For instance,
A-Scan and UBM rely on ultrasound; Orbscan and
Orbscan II rely on scanning-slit topography; Pentacam,
Pentacam HR and Galilei use Scheimpflug photography;
Visante OCT uses low coherence interferometry;
IOLMaster uses a lateral slit illumination and is based
on partial coherence interferometry; whereas Lenstar
measures ACD with optical biometry. Other sources
of discrepancies may be the age group included in each
study and the ability of the researcher to control the
accommodation state during measurement in those
studies that included young subjects.
Finally, further studies should be undertaken, aimed
as studying the interchangeability of ACD measurements
across different age groups, ocular conditions and
interchangeability with other devices. It would also be
interesting to define a relationship between the gold
standard for ACD and the rest of the devices that are
able to measure these distances. This would be useful
for surgeons who could then know the ACD that a gold
standard would yield without the need for having the
device in the ophthalmology clinic. As a result, some
postsurgical problems, such as those related to IOL
power, could be avoided.
To conclude, Pentacam (for phakic eyes) and
Pentacam HR (for cataractous eyes) can be used
interchangeably with the two gold standards used to
measure ACD (IOLMaster and A-Scan). This review
also reveals that the interchangeability of the device
depends on the patients’ ocular condition and this must
be taken into consideration in clinical practice.
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JOURNAL OF EMMETROPIA - VOL 3, OCTOBER-DECEMBER
First author:
Alberto Domínguez Vicent, MSc
Optometry Research Group (GIO),
Valencia (Spain)