·Review··Current Issue· ·Achieve· ·Search Articles· ·Online Submission· ·About IJO· PMC
Device interchangeability on
anterior chamber depth and white-to-white measurements: a thorough literature review
Alberto
Domínguez-Vicent, Cari Pérez-Vives, Teresa Ferrer-Blasco, Santiago García-Lázaro, Robert Montés-Micó
Optometry Research Group (GIO),
Department of Optics and Optometry and Visual Science, University of Valencia,
Valencia 46100, Spain
Correspondence to: Alberto Domínguez-Vicent. Department of
Optics and Optometry and Visual Science, University of
Valencia, C/ Dr Moliner,
50-46100-Burjassot, Spain.
alberto.vicent@uv.es
Received: 2015-09-28
Accepted: 2015-11-03
Abstract
We have reviewed a set of recently published studies
that compared the anterior chamber depth (ACD) and/or white-to-white (WTW)
distance obtained by means of different measuring devices. Since some of those
studies reached contradictory conclusions regarding device interchangeability,
this review was carried out in attempting to clarify which clinical devices can or cannot be considered as
interchangeable in clinical practice to measure ACD and/or WTW distance, among
these devices: A-scan, ultrasound biomicroscopy, Orbscan and Orbscan II
(Bausch&Lomb Surgical Inc., San Dimas, California, USA), Pentacam and
Pentacam HR (Oculus, Wetzlar, Germany), Galilei (Ziemer, Switzerland), Visante
optical coherence tomography (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).
KEYWORDS: anterior camber depth measurement; white to white measurement; device interchangeability; anterior chamber eye
Citation: Domínguez-Vicent A,
Pérez-Vives C, Ferrer-Blasco T, García-Lázaro S, Montés-Micó R. Device interchangeability on anterior chamber depth and white-to-white
measurements: a thorough literature review. Int J Ophthalmol 2016;9(7):1057-1065
INTRODUCTION
Nowadays, the measurement of anterior chamber depth
(ACD) and white-to-white (WTW) distance has become increasingly important in
ophthalmic practice, for instance, when it comes to planning
cataract[1-3] and
refractive[1-6] surgery,
calculating phakic or pseudophakic intraocular lens (IOL)[3,7-10] power and diameter, screening glaucoma risk
factors[2,9,11], and so
on. Many papers have been published focusing on device interchangeability to
measure ACD or WTW distance. However, some of these studies show discrepancies
in their findings.
The inclusion criterion was that the study had to
evaluate device interchangeability across two or more devices for the
measurement of ACD or WTW distance. The devices included in this review were:
A-scan, ultrasound biomicroscopy (UBM), Orbscan and Orbscan II (Bausch&Lomb
Surgical Inc., San Dimas, California, USA), Pentacam and Pentacam HR (Oculus,
Wetzlar, Germany), Galilei (Ziemer, Switzerland), Visante optical coherence
tomography (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 work was to clarify
which devices are interchangeable to measure ACD or WTW distance values. A
brief description of the measuring principle use of each device was also
included. Finally, readers
should consider that a brief description of each study methodology was included
only the first time we mentioned the study.
Method of Literature Search Articles studying device
interchangeability or these ones that compare ACD or WTW distances among the
devices included in this study were identified through a multistage systematic
approach. First, we conducted a computerized search in MEDLINE database using PubMed
(www.pubmed.com). A comprehensive search was made using the terms: ACD
device interchangeability, WTW device interchangeability, ACD measurement, WTW
measurement, and all of those terms followed by “AND”and
the following: A-scan interchangeability, UBM interchangeability, Orbscan
interchangeability, Pentacam interchangeability, Galilei interchangeability,
Visante OCT interchangeability, IOLMaster interchangeability, and Lenstar
interchangeability interchangeability.
Second, all entries were critically reviewed and those
considered to be of significative were used, including those written in
English, Spanish, and Germany, and also those from the non-English literature
if an English abstract was available. Next, we reviewed the reference section
of each article, to detect other studies not captured by the MEDLINE search.
Once these articles were critically reviewed, they were included if there were
considered to add additional data or to refute previous information.
Measuring Principle
A-scan This ultrasound contact device is used
to measure eye biometric dimensions, i.e.
axial length, ACD, 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 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 rule over the echography.
Orbscan The Orbscan is a noncontact topography
system that is used for anterior segment evaluation. It uses the horizontally
moving scanning camera to acquire slit images. After image reconstruction, a
mathematical three-dimensional model of the cornea and the anterior segment is
calculated. To calculate the ACD, the software detects automatically the
corneal endothelium surface and anterior surface of the crystalline lens on the
acquired images.
Orbscan II The Orbscan II 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 as Orbscan.
Pentacam The Pentacam is a non-contact device
using a rotating Scheimpflug camera. It uses a monochromatic slit light source
to measure the anterior segment topography. It takes 50 images in 2s with a
maximum of 25 000 measured points The internal software creates a
three-dimensional reconstruction of the anterior segment by using the elevation
data of these images, which gives information about anterior and posterior
surface of the cornea, and ACD from endothelium to crystalline lens.
Pentacam HR Pentacam HR 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. This device takes
50 images in 2s with a maximum of 138 000 measured points. The internal software creates a three-dimensional
reconstruction of the anterior segment by using the elevation data of these
images, giving information about anterior and posterior surface of the cornea,
and ACD from endothelium to crystalline lens.
Galilei The Galilei 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 optical coherence
tomography Visante OCT is a time domain
non-invasive system that employs high-resolution images. The light source is a
superluminiscent light-emitting diode with a short wavelength that has 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
4000 axial scans/s, and each image frame has 500 axial scans/image. It can be
used to measured central corneal thickness and ACD.
IOLMaster The IOLMaster is designed to measure
the parameters used in 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. ACD is
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 optical biometer is based
on low coherence reflectometry, with an 820-mm superluminiscent diode. The
Lenstar detects the 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.
EyeSys The EyeSys topographer uses a Placido
disc-based data acquisition system designed for rapid and quantitative
photokeratoscopy, to capture the anterior segment’s topographic features. The
computer calculates the corneal diameter automatically.
Anterior Chamber Depth Device Interchangeability Table 1 includes mean difference and 95% limit of
agreement obtained after each device comparison for phakic eyes. Studies
included in this section compared at least two of the following devices:
A-scan, UBM, Orbscan, Orbscan II, Pentacam, Pentacam HR, Galilei, Visante OCT,
IOLMaster, and Lenstar.
Table 1 Mean
difference between each pair device comparison for healthy eyes
mm
|
Anterior segment system |
A-scan |
UBM |
Orbscan |
Orbscan
II |
Pentacam |
Pentacam
HR |
Galilei |
Visante
OCT |
IOLMaster |
Lenstar |
|
A-scan |
|
- |
- |
0.03±0.01[2] |
0.02[5]; 0.10[12] |
0.19[13] |
- |
- |
0.10±0.14[2]; 0.01[12] |
0.27±0.32[14] |
|
UBM |
- |
|
- |
0.08±0.09[15] |
- |
- |
- |
0.07±0.09[16] |
- |
- |
|
Orbscan |
- |
- |
|
- |
0.04±0.06[7]; 0.14[17] |
- |
- |
0.10[17] |
- |
- |
|
Orbscan
II |
0.03±0.01[2] |
0.08±0.09[15] |
- |
|
0.08±0.04[4]; 0.05±0.02[11]; 0.17[18]; 0.05[19] |
0.30±0.04[20] |
0.32±0.05[20] |
0.15±0.05[4] 0.06±0.03[11] |
0.01[1]; 0.12±0.07[2]; 0.04±0.12[9]; 0.16±0.09
[11]; 0.06[19] |
- |
|
Pentacam |
0.02[5]; 0.10[12] |
- |
0.04±0.06[7]; 0.14[17] |
0.08±0.04[4]; 0.05±0.02[11]; 0.17[18]; 0.05[19] |
|
- |
- |
0.07±0.04[4]; 0.02±0.02
[11]; 0.04 [17]; 0.07 [21] |
0.02[6]; 0.05[8]; 0.03[10];0.12±0.09[11]; 0.09[12]; 0.11[19] |
0.03
[21]; 0.02±0.07
[22] |
|
Pentacam
HR |
- |
- |
- |
0.30±0.04[20] |
- |
|
0.02±0.01[20] 0.07±0.11[23] |
- |
0.05[24] |
- |
|
Galilei |
- |
- |
- |
0.32±0.05[20] |
- |
0.02±0.01[20] 0.07 ± 0.11[23] |
|
- |
- |
- |
|
Visante
OCT |
- |
0.07±0.09[16] |
0.10[17] |
0.15±0.05[4] 0.06±0.03[11] |
0.07±0.04
[4]; 0.02±0.02[11]; 0.04[17]; 0.07[21] |
- |
- |
|
0.10±0.08[11] 0.06±0.01[25] |
0.10[21] |
|
IOLMaster |
0.10±0.14[2]; 0.01[12] |
- |
- |
0.01[1]; 0.12±0.07[2];0.04±0.12[9];0.16±0.09[11]; 0.06[19] |
0.02[6]; 0.05[8]; 0.03[10]; 0.12±0.09[11]; 0.09[12]; 0.11[19] |
0.05[24] |
- |
0.10±0.08[11] 0.06±0.01[25] |
|
- |
|
Lenstar |
0.27±0.32[14] |
- |
- |
- |
0.03[21]; 0.02±0.07[22] |
- |
- |
0.10 (0.27)[21] |
- |
|
A-scan vs Orbscan II There is one study (Hashemi et al[2]) that compared A-scan with Orbscan II
for the measurement of ACD in healthy eyes (Table 1). They obtained comparable
results between these devices, the mean difference and the 95% limits of
agreement width being 0.03±0.01 mm and 0.45 mm, respectively. These authors concluded that differences between these
devices might be clinically negligible depending on the parameter measured.
From the mean difference and limits of
agreement obtained in this study, there is a 95% chance that Orbscan II will
measure 0.25 mm shallower and 0.20 mm deeper ACD than EchoScan. These
differences were clinically significant to estimate IOL vault, but were not to
calculate IOL power, as IOL power varies by 0.25 D for each 0.6 mm of ACD[26].
Then, from Hashemi et al[2]
results it can be concluded that depending on anterior eye measurement, these
devices they can or cannot be used interchangeable.
However, these authors included both eyes from their
healthy volunteers, and a possible bias could be included in this study. As was
explained by McAlinden et al[27], paired data
simply doubles the number of data points that were included in the study and
the statistical power test was reduced. Then, further studies should avoid this
bias to confirm if these devices can be used interchangeable.
A-scan vs Pentacam Nemeth et al[5] and Elbaz et al[12] compared ACD measurements using A-scan
and Pentacam in phakic and healthy eyes. The latter study obtained that
Pentacam measured significant higher ACD than A-scan, which limits of agreement
width was 0.59 mm. According to Elbaz et al[12] results, they concluded that device difference was
broad enough to be clinical significant. Then, they concluded that for some
clinical applications these devices couldn’t be used interchangeable.
Considering Food and Drug Administration (FDA) tolerance values[28], these devices are interchangeable to assess IOL
power but they are not to assess IOL vault.
On the other hand, Nemeth et al[5] obtained comparable measurements,
which mean difference was 0.02 mm.
They concluded that these devices should be used interchangeable in clinical
practice. Despite of this conclusion, the method used to study device agreement
was not correct. In this sense, they performed a linear regression analysis,
and as was reported by Bland and Altman[29], this method
measures the strength of a relation between two variables, not the agreement
between them. Then, after these studies, it seems that these devices can be
used interchangeable to measure ACD distance.
A-scan vs Pentacam HR Szalai et al[13] compared
the ACD measures that A-scan and Pentacam HR provide in healthy eyes. They
observed that A-scan yielded significantly higher ACD values than Pentacam HR,
the limit of agreement being 0.56 mm. Thus
concluding that these two devices cannot be assumed to be interchangeable in
clinical practice. However, according to Nuvita Nomogram, the required IOL power varies by 0.10 D for each 0.20 mm of ACD. So from Szalai et al[13] results, device difference is not
clinical significant to calculate IOL power, but, to estimate IOL vault device
difference is significant[28].
A-scan vs IOLMasterA total of two studies[2,12]compared ACD
measurements between A-scan and IOLMaster. Hashemi et al[2] and Elbaz et al[12]
obtained contradictory results: while the former one obtained that the
IOLMaster measuring significant higher ACD than A-scan (the 95% limits of
agreement width being 0.54 mm),
the latter one did the opposite trend (the 95% limits of agreement being 0.65 mm). Despite these differences between
both studies, they concluded that differences between A-scan might be
clinically negligible depending on the use of the measurement. In this sense,
to calculate IOL power these differences are negligible and to assess IOL vault
they are not.
A-scan vs Lenstar Gursoy et al[14] has compared A-scan with Lenstar for
the measurement of ACD in children eyes under cyclopegia. They included 530
eyes with A-scan and 557 eyes with the Lenstar, the former device measuring
significant shallower ACD than the last one (the 95% limit of agreement being
1.24 mm). Despite these findings, they
concluded that mean difference was clinically insignificant for IOL power
calculation. However, this conclusion is based on mean bias alone, and as has
been recommended[27],
conclusions about device interchangeability should be based on mean bias and limits
of agreement, instead of consider the mean bias alone. Consequently, according
to their results, these devices can be used interchangeable to calculate IOL
power, but they are not to assess IOL vault.
Ultrasound biomicroscopy vs
Orbscan II Only one study so far, carried out by
Lee et al[15], have compared UBM with Orbscan II for the
measurement of ACD in healthy eyes, and the UBM measured significant shallower
ACD than Orbscan II, the mean difference being 0.08±0.09 mm, thus
concluding that these differences were not clinically meaningful. However, this
conclusion should not be considered because the analysis used to assess device
agreement was incorrect. As was proposed by Bland and Altman[29], the limits of agreement between both devices should
be used to assess device agreement, instead of using only the mean bias. Then,
there is not sufficient information to conclude if these devices can be used as
interchangeable. Consequently, further studies should clarify it.
Ultrasound biomicroscopy vs
Visante optical coherence tomography Only one study so far (Zhang et al[16])
has included an ACD comparison between UBM and Visante OCT in phakic eyes. The
mean difference was 0.07±0.09 mm
and the limit of agreement width was 0.36 mm. Finally, these authors concluded that UBM and
Visante OCT measurements were interchangeable in phakic eyes.
As was proposed by McAlinden et al[27]
clinical interpretation is an essential attribute to determine device
interchangeability. Then, if the required IOL power is considered to vary by
0.10 D for each 0.20 mm of ACD, difference for phakic eyes
were not clinically significant, but they were significant to IOL safety[28].
Orbscan vs Pentacam Lackner et al[7]
and Yazici et al[17] studied the agreement between Orbscan with Pentacam
in healthy eyes. The former one obtained that the Scheimpflug device resulted
with shallower values than the Orbscan; meanwhile the latter study obtained the
opposite. In one study, the mean difference was 0.04±0.06 mm[7]and
in the other was 0.14 mm[17]. Moreover, both
authors concluded that differences between both devices were small to create
any noticeable difference in refractive outcome, the limit of agreement width
being 0.25 mm in Lackner et al[7]
study and 0.45 mm in Yazici et al[17]
one. However, it should be considered that differences were clinical
significant to assess IOL vault[28].
On the other hand, these authors included both eyes of each volunteer, and
include both eyes from healthy volunteers only increases sample size and could
reduce statistic power because of eye symmetry. Then, further studies should
clarify device interchangeability.
Orbscan vs Visante
optical coherence tomography Yazici et al[17], also compared ACD
values yielded by Orbscan and by Visante OCT. Comparable results were obtained
between these devices, the width of the limits of agreement being 0.54 mm. These authors concluded that these
differences were small and did not influence decisions for refractive surgery.
However, it should be specified that for IOL power calculation these
differences were not significant, but to evaluate IOL safety[28] these differences
were significative.
Orbscan II vs
Pentacam Four studies[4,11,18-19] assessed the interchangeability
between Orbscan II and Pentacam in healthy eyes. Contradictory results were
obtained among these studies because Dinc et
al[11] obtained
comparable results between these devices, and the other studies obtained that
Orbscan II measured significant shallower ACD distances than Pentacam.
Moreover, contradictory conclusions were also obtained: while Doors et al[4] and Dinc etal[11] concluded that
these devices should not be use interchangeable, the other two authors[18-19]
did the opposite. Differences in sample characteristics could explain these
contradictions. In this sense, Dinc et al[11] included
emmetropic volunteers and Hashemi andMehravaran[18] and Utine et al[19]
included myopic ones. Unfortunately, Doors et
al[4] did not specified
volunteers’ characteristics. Independently of these contradictions, it was
observed that Pentacam tends to measure deeper ACD than Orbscan II in all
studies.
Finally, according
to these studies it seems that Orbscan II measures shallower ACD values than Pentacam. This could be due
to the relatively low-depth resolution of slit scanning compared to Pentacam[30].
However, contradictions about device interchangeability between healthy eyes
should be clarified. On the other hand, a possible bias was observed in these
studies because of all of them, except Utine et al[19], included both eyes of each volunteer. As was
explained before, include both eyes from a healthy volunteer adds little
information because of eye symmetry. Consequently, the sample size was
increased and the statistical test power could be decreased.
Orbscan II vs
Pentacam HR Salouti et al[20]
compared ACD values yielded by Orbscan II and Pentacam HR as a function of
volunteer’s ACD. They divided the sample size in: ACD less than 3.00 mm, ACD between 3.00 and 3.50 mm and ACD deeper than 3.50 mm. For the middle group, the Orbscan
II measured significant deeper ACD than Pentacam HR, the mean difference and
limits of agreement being 0.27±0.06 mm and from -0.26 to 0.80 mm,
respectively. This behavior was also observed for the deepest ACD group, the
mean difference and 95% limits of agreement width being 0.46±0.02 mm and from 0.38 to 0.54 mm, respectively. However comparable
results were obtained for the lowest one. Finally, these authors concluded that
differences between these devices were not within clinically acceptable levels
and they are not interchangeable in every clinical situation. However,
according to their limits of agreement, differences between these devices were
not clinical significant to calculate IOL power, but they were to assess IOL
vault[28], which maximum width was 1.14 mm.
Finally, according
to this study, it seems that Orbscan II
measures higher ACD values than Pentacam HR. However, a possible bias was
observed in this study because both eyes of each volunteer were included.
Consequently, the sample size was duplicated and the power of the statistical
test could be virtually decreased. So further studies should clarify device
agreement.
Orbscan II vs Galilei Salouti et al[20]
also studied the interchangeability between Orbscan II and Galilei as a
function of volunteer’s ACD, and comparable results were only obtained for the
shallowest ACD group. Moreover, differences between Orbscan II and Galilei were
not within clinically acceptable levels, whose maximum and minimum limit of
agreement width was 1.14 mm (for the shallowest group) and 0.12 mm (for the deepest ACD group),
respectively. After these results, they concluded that differences between
these devices were not within clinically acceptable levels, and Orbscan II and
Galilei should not be used interchangeably in every clinical situation.
However, if 0.47 mm is subtracted for subjects whose ACD is deeper than
3.50 mm, the Orbscan II measurement will be
equivalent to this obtained with the Galilei. Nevertheless, it should be
considered that both eyes were included and the power of the statistical test
could be virtually decreased.
Orbscan II vs Visante optical coherence tomography Doors et al[4] and Dinc et al[11], compared Orbscan II with Visante OCT
for the measurement of ACD in healthy eyes. Both studies obtained that Visante
OCT produced significantly deeper ACD values than Orbscan II. Although the mean
difference between these devices was small (0.15±0.05 mm[4] and 0.06±0.03 mm[11]), both authors concluded that these
devices cannot be use interchangeable because the 95% limits of agreement were
large and clinically relevant (0.18 mm[4] and 0.10 mm[11]). However, if the required IOL power
is considered to vary by 0.10 D for each 0.20 mm of ACD, about 0.30 mm difference, which corresponds to
the highest difference obtained with these authors, is not clinically
significant. Then, it can be concluded that these devices can be used
interchangeable to calculate IOL power, but not to assess IOL vault.
Orbscan II vs
IOLMaster Five studies[1-2,9,11,19] have compared Orbscan II with
IOLMaster with dissenting findings, after measuring ACD in healthy volunteers.
While Frisch et al[1], Hashemi et al[2] and Dinc et al[11],
obtained that Orbscan II measured shallower ACD than IOLMaster, Rosa et al[9] and Utine et al[19] obtained the opposite trend. Despite
these contradictions, four of these studies[1-2,9,19] concluded that these devices can be
used interchangeable and only one[11] concluded the opposite.
Although these studies concluded that these devices
should be used interchangeable to measure ACD in healthy eyes, some of them did
not specify when employ both devices interchangeable. Then, according to
previous studies, Orbscan II and IOLMaster can be used interchangeable to
calculate IOL power, but not to assess IOL safety. Finally, after these
results, it seems that Orbscan II measures shallower ACD distances than
IOLMaster. This could be because of IOLMaster measures ACD away from the centre
as the slit source comes from the temporal side, which may also result in a higher
ACD measurement[11].
Pentacam vs Visante optical coherence tomography Doors et al[4],
Dinc et al[11], Yazici et al[17] and O’Donnell et al[21]
assessed device agreement between Pentacam and Visante OCT. No statistically
significant differences were found neither by Dinc et al[11] nor by Yazici et al[17]
and nor O’Donnell et al[21].
Contrariwise, Door et al[4] obtained that Visante OCT measured
significantly deeper ACD values than Pentacam, the mean difference and limits
of agreement width being 0.07±0.04 mm and 0.16 mm, respectively. Despite these
results, three studies[4,11,21] concluded that these devices should
not be used interchangeable, and only one[17] concluded the opposite. Independently
of these contradictions, from limits of agreement obtained in each study, it
can be concluded that differences between device measurements were not clinical
significant to calculate IOL power but they were to estimate IOL vault.
Pentacam vs IOLMaster Six studies[6,8,10-12,19] have so far compared Pentacam with
IOLMaster for the measurement of ACD with distending results: two studies[6,11] obtained that
Pentacam measured shallower ACD than IOLMaster and the others[8,10,12,19] obtained
the opposite trend. Contradictory conclusions were also obtained: while Dinc et al[11] and Elbaz et
al[12] concluded that
differences were clinical significant, Savant et al[6],
Reuland et al[8], Woodmass and Rocha[10] and Utine et al[19]
concluded the opposite. Despite these contradictions, according to limits of
agreement and that IOL power varies by 0.25 D for each 0.60 mm of ACD[26] it can be concluded that differences obtained with
these devices was within clinical tolerance level to use them in the clinical
practice as interchangeable to calculate IOL power. However, to estimate IOL
vault, these devices should not be used interchangeable.
Pentacam vs Lenstar Only two studies so far[21-22] have compared Pentacam with Lenstar as
far as ACD measurement is concerned. Similar results obtained between these
studies: the 95% limit of agreement width obtained in both studies was smaller
than 0.30 mm and the mean difference was less than 0.05 mm in both studies. However,
contradictory conclusions were achieved in each study: while O’Donnell et al[21] concluded that these devices should
not be used interchangeable, Huang et al[22] concluded the opposite. Contradictions
between these studies could be related to differences in sample size. While
O’Donnell et al[21] included 27 subjects, Huang et al[22] included 108 ones. However, according
to these results, differences between these devices seems to be clinical
significant to assess IOL vault but to assess IOL power they do not.
Pentacam HR vs
Galilei Salouti et al[20],
who studied device interchangeability as a function of volunteer ACD, obtained
that the 95% limit of agreement width within all groups was lower than 0.25 mm. These authors concluded that
differences were within clinical acceptable levels, so they can be used
interchangeable. However, it should be specified that they are interchangeable
to calculate IOL power, but to assess IOL safety they cannot[28]. It should be in
mind that these authors included both eyes, so the sample size was increased
and the statistical test power could be decreased. On the other hand, another study[23] also assessed the
agreement between these devices and only one eye per patient was included.
According to that study, the 95% limit of agreement width was 0.43 mm, and
the authors concluded that these devices should not be used as interchangeable
to estimate the IOL vault, but they could be to estimate the IOL’s power to
implant.
Pentacam HR vs
IOLMaster Németh et al[24],
assessed agreement between Pentacam HR and IOLMaster. Comparable results were
obtained between these devices, the mean difference (0.05 mm) and limits of agreement (from
-0.40 mm to 0.30 mm) being within clinical tolerance
levels to assess IOL power. But, differences between both devices were not
within clinical tolerance level to assess IOL vault[28]. However, a bias could be included in this study
because they both healthy eyes were measured. Thus, this only increases sample
size and does not include new information. Then, further studies should confirm
Nemeth et al’s[24] conclusions.
Visante optical coherence
tomographyvs IOLMaster Two studies[11,25] have compared Visante OCT and
IOLMaster for the measurement of ACD in healthy eyes. Contradictory results and
conclusions were obtained: while Dinc et
al[11] found that the IOLMaster measured
significantly deeper ACD, Lavanya et al[25] obtained the
opposite trend. Regarding to these studies, Dinc et al[11] concluded that these devices should
not be used interchangeably to measure ACD, and Lavanya et al[25]
concluded the opposite. Contradictions between these studies could be related
to sample bias observed in Dinc et al[11] study, who
measured both eyes of each volunteer (they increased sample size and could
decrease the statistical power test). So, from Lavanya et al[25]
it can be we concluded that Visante OCT and IOLMaster can be used interchangeable
to assess IOL power in clinical practice.
Visante optical coherence
tomographyvs Lenstar O’Donnell et
al[21] also
compared ACD values measured with Visante OCT and Lenstar. These authors
obtained significantly deeper ACD values with Visante OCT, the mean difference
and limit of agreement with being 0.10 mm and 0.27 mm, respectively. After these results,
they concluded that these two devices should not be used interchangeably in the
clinical practice. Nonetheless, the limit of agreement range between Visante
OCT and Lenstar lied within clinical acceptable tolerance level to calculate
IOL power, which suggests that these devices could be considered
interchangeable in clinical practice. However, to assess IOL vault, they cannot
be interchangeable.
White-to-white Distance Device Interchangeability
Table 2 lists the eight comparative studies in which
the WTW distance was measured using two or more of the following devices: UBM,
Orbscan, Orbscan II, Pentacam, Galilei, Visante OCT, IOLMaster, Lenstar and
EyeSys. The table also summarises the results of each study (mean WTW
distance±standard deviation).
Table 2 Mean difference between each pair
device comparison for healthy eyes for WTW distance
(mm)
|
Anterior segment system |
UBM |
Orbscan II |
Pentacam |
Pentacam HR |
Galilei |
Visante OCT |
IOLMaster |
Lenstar |
EyeSys |
|
UBM |
|
- |
0.86±0.43[31] |
- |
- |
0.71±0.26[31] |
- |
- |
- |
|
Orbscan II |
- |
|
- |
- |
0.38±0.56[3] |
0.68±0.26[32] |
0.32±0.11[32] |
- |
0.42±0.78[3] |
|
Pentacam |
0.86±0.43[31] |
- |
|
- |
- |
0.15±0.50[31] |
- |
- |
- |
|
Pentacam HR |
- |
- |
- |
|
0.05±0.39[23] |
- |
- |
- |
- |
|
Galilei |
- |
0.38±0.56[3] |
- |
0.05±0.39[23] |
|
- |
- |
- |
0.05±0.75[3] |
|
Visante OCT |
0.71±0.26[31] |
0.68±0.26[32] |
0.15±0.50[31] |
- |
- |
|
0.36±0.18[32] |
- |
- |
|
IOLMaster |
- |
0.32±0.11[32] |
- |
- |
- |
0.36±0.18[32] |
|
0.06[33] |
- |
|
Lenstar |
- |
- |
- |
- |
- |
- |
0.06[33] |
|
- |
|
EyeSys |
- |
0.42±0.78[3] |
- |
- |
0.05±0.75[3] |
- |
- |
- |
|
Ultrasound biomicroscopy vs
Pentacam Kim et al[31] studied device
agreement to measure internal WTW, and they obtained that UBM measured
significant lower WTW than Pentacam. Moreover, the limit of agreement width
between these devices was 0.84 mm. Considering FDA tolerance limits and that IOLs are
sized to the nearest 0.50 mm, it can be concluded that these devices cannot be
used interchangeable. However, these authors included both eyes of each
volunteers. So, the sample size was increased and the statistical test power
could be reduced. Then, further studies should avoid this bias to clarify
whether or not UBM and Pentacam can be used interchangeable.
Ultrasound biomicroscopy vs Visante optical
coherence tomography Kim et al[31] also studied agreement between UBM and
Visante OCT to measure WTW distance. They obtained that UBM measured
significant lower WTW values than Visante OCT, the width of limit of agreement
being 0.51 mm. Despite these findings, these
authors concluded that these devices should be used interchangeably. However,
the mean difference and limits of agreement were large enough to be within
clinical acceptable levels when it comes to calculate anterior-chamber IOL diameter.
Then, it can be concluded that these devices cannot be used interchangeable to
measure WTW distance. However, these authors included both eyes of each
volunteers. So, the sample size was increased and the statistical test power
could be reduced. Then, further studies should avoid this bias to clarify
whether or not UBM and Pentacam can be used interchangeable.
Orbscan II vs Galilei Salouti et al[3]studied
the interchangeability of Orbscan II and Galilei, obtaining that Galilei
provides significantly higher WTW values than Orbscan II (the limits of
agreement width being 2.20 mm). After this study it can be concluded that these
devices cannot not be considered as interchangeable to measure WTW distances in
the clinical practice. A possible bias was observed in this study because of
Salouti et al[3] included both eyes and it increases the sample size
and could reduce the statistical power test. Consequently, further studies
should be done to confirm the device agreement.
Orbscan II vs Visante optical coherence tomography Kohnen et al[32]assessed
the interchangeability of Orbscan II and Galilei. The mean difference between
these devices was about 0.68 mm and the limits of agreement width was about
0.90 mm. However, the mean difference and limits of agreement were large enough
to be within clinical acceptable levels when it comes to calculate
anterior-chamber IOL diameter. Then, it can be concluded that these devices
should not be used interchangeable to measure WTW distance.
Orbscan II vs
IOLMaster Kohnen et al[32] studied the interchangeability of Orbscan II and
IOLMaster. Comparable results between these devices, the limits of agreement
width being about 0.45 mm[32].
According to results obtained in these studies, the mean difference and limits
of agreement between Orbscan II’s and IOLMaster’s values exceeded the tolerance
limit for the calculation of anterior-chamber IOLs. However, this study
included both eyes of each volunteers, and as was said, the sample size was
increased and the statistical test power could be reduced. Then, further
studies should be carried out to assess device interchangeability.
Orbscan II vs EyeSys One study (Salouti et al[3]) has so far compared Orbscan II and EyeSys for the
measurement of WTW distance, obtaining significantly lower values with Orbscan
II the limits of agreement width being 3.06 mm. Therefore, as IOLs are size to the
nearest 0.50 mm, it can be concluded that these
devices cannot be used interchangeable to measure this distance. A possible
bias was observed in this study because of Salouti et al[3] included both eyes and it only
increases sample size and could decrease the statistical test power.
Consequently, further studies should be done to confirm the device agreement.
Pentacam vs Visante
optical coherence tomography Kim et al[31] studies internal horizontal anterior
chamber diameter measured with Pentacam and Visante OCT. They obtained
comparable results, but the 95% limits of agreement were big enough (1.97 mm) to be clinical significant. Then,
it can be concluded that these devices cannot be used interchangeable in
clinical practice. These authors included a possible bias in the study because
they included both eyes of each volunteer. Consequently, further studies should
confirm this device agreement.
Pentacam HR vs Galilei One study[23] assessed the agreement between the Pentacam HR and
Galilei to measure WTW distances. According to that study, the Pentacam HR
measured in average 0.05 mm wider WTW distances than the Galilei. Nevertheless,
the 95% limits of agreement was big enough to be clinical significant, and
consequently these authors suggested no to use these instruments as
interchangeable in clinical practice.
Galilei vs EyeSys One study (Salouti et al[3]) has to date compared Galilei and EyeSys for the
measurement of WTW distance. Comparable results were obtained between these
devices, the 95% limits of agreement being without clinical tolerance levels.
Then, it can be concluded that Dual Scheimpflug device and EyeSys cannot be use
interchangeable in clinical practice. A possible bias was observed in this
study because of Salouti et al[3] included both eyes and it only increases sample size
and could decrease the statistical test power. Consequently, further studies
should be done to confirm this device agreement.
IOLMaster vs Lenstar A study[33] measured WTW distance with these
devices, and comparable results were obtained. In this sense, Montés-Micó et al[33] obtained comparable WTW distances.
However, according to device agreement obtained in this study can be concluded
that IOLMaster and Lenstar cannot be used interchangeable.
CONCLUSION
Anterior Chamber Depth There present review reveals that the device pairs
included cannot be used to assess IOL safety. However, the device pair that can
be used interchangeable to calculate IOL power, are A-scan-Pentacam,
A-scan-Pentacam HR, A-scan-IOLMaster, A-scan-Lenstar; UBM-Pentacam and
UBM-VisanteOCT; Orbscan-VisanteOCT; OrbscanII-Pentacam, OrbscanII-VisanteOCT
and OrbscanII-IOLMaster; Pentacam-VisanteOCT, Pentacam-IOLMaster and
Pentacam-Lenstar; VisanteOCT-IOLMaster and VisanteOCT-Lenstar;
IOLMaster-Lenstar.
Regarding to discrepancies across the studies that
have been analysed, they may be due to differences in the measurement method
upon which each device is based. For instance, A-scan and BMU 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 can be the age group included
in each study and the ability of the researcher to control the accommodation
state during the measurement in those studies that included young subjects.
As was said by Bland and Altman[29], methods which agree well enough for one purpose may
not agree well enough for another. This explains why some devices have good
agreement to measure IOL power and to estimate IOL vault they did not agree. On
the other hand, further studies, should use a Bland-Altman procedure to assess
device agreement and include only one eye to avoid a possible bias. Moreover,
all of them should specify the clinical application that the device pair should
be used.
White-to-white After these results it can be concluded that any device
comparison showed good agreement between device compared. Differences between
each device could be related with differences in digital image processing
carried out by each WTW measurement. Computers compare grey-scale steps to
detect the limbus point-which lies between the white sclera and the darker iris
image-and then calculate the corneal
diameter. As a result, this measurement is affected by anything that induces
some darkness during the measurement; for instance, eyelash shadow, nose shadow
or device shadow. Consequently, any corneal disease affecting corneal
transparency will have an impact upon the resulting WTW value. Therefore, to
measure WTW distances a method that remains unaffected by shadows or ocular
artefacts should be used. If this was not possible, the angle-to-angle or
sulcus-to-sulcus distance should be measured instead for the calculation of
anterior-chamber IOLs or posterior-chamber IOLs, respectively. Moreover, it
should be born in mind that these two last measures are more useful when it
comes to calculating anterior-chamber width or IOL size.
As for ACD and WTW, further studies should be
undertaken, aiming to study the interchangeability of ACD measures across
different age groups, ocular conditions and the interchangeability across other
devices. Moreover, other studies should clarify the devices pair which
interchangeability is yet unclear. Moreover, it should be interesting to attain
a relationship between the gold standard for ACD and WTW and the rest of the
devices that are able to measure these distances. For surgeons it would be
useful because they could know the ACD or WTW that a gold standard would yield
without the need to have the device it in the ophthalmology clinic.
Consequently, it would avoid some postsurgical problems, as pupil ovalization
or problems related to IOL power.
ACKNOWLEDGEMENTS
Conflicts of Interest: Domínguez-Vicent A, None; Pérez-Vives C, None; Ferrer-Blasco T, None; García-Lázaro S, None; Montés-Micó R, None.
REFERENCES
1 Frisch I, Rabsilber T, Becker K, Reuland A, Auffarth
G. Comparison of anterior chamber depth measurements using Orbscan II and
IOLMaster. Eur J Ophthalmol
2007;17(3):327-331. [PubMed]
2 Hashemi H, Yazdani K, Mehravaran S, Fotouhi A.
Anterior chamber depth measurement with a-scan ultrasonography, Orbscan II, and
IOLMaster. Optom Vis Sci
2005;82(10):900-904. [PubMed]
3 Salouti R, Nowroozzadeh M, Zamani M, Ghoreyshi M,
Salouti R. Comparison of horizontal corneal diameter measurements using
Galilei, EyeSys and Orbscan II systems. Clin
Exp Optom 2009;92(5):429-433. [CrossRef] [PubMed]
4 Doors M, Cruysberg L, Berendschot T, de Brabander
J, Verbakel F, Webers C, Nuijts R. Comparison of central corneal thickness and
anterior chamber depth measurements using three imaging technologies in normal
eyes and after phakic intraocular lens implantation. Graefes Arch Clin Exp Ophthalmol 2009;247(8):1139-1146. [CrossRef] [PubMed]
[PMC free article]
5 Nemeth G, Vajas A, Kolozsvari B, Berta A, Modis
LJ. Anterior chamber depth measurements in phakic and pseudophakic eyes:
Pentacam versus ultrasound device. J
Cataract Refract Surg 2006;32(8):1331-1335. [CrossRef] [PubMed]
6 Savant V, Chavan R, Pushpoth S, Ilango B.
Comparability and intra-/interobserver reliability of anterior chamber depth
measurements with the Pentacam and IOLMaster. J Refract Surg 2008;24(6):615-618. [PubMed]
7 Lackner B, Schmidinger G, Skorpik C. Validity and
repeatability of anterior chamber depth measurements with Pentacam and Orbscan.
Optom Vis Sci 2005;82(9):858-861. [CrossRef]
8 Reuland M, Reuland A, Nishi Y, Auffarth G. Corneal
radii and anterior chamber depth measurements using the IOLmaster versus the
Pentacam. J Refract Surg
2007;23(4):368-373. [PubMed]
9 Rosa N, Lanza M, Capasso L, Lucci M, Polito B,
Romano A. Anterior chamber depth measurement before and after photorefractive
keratectomy: comparison between IOL master and Orbscan II. Ophthalmology 2006;113(6):962-969. [CrossRef] [PubMed]
10 Woodmass J, Rocha G. A comparison of Scheimpflug
imaging simulated and Holladay equivalent keratometry values with partial
coherence interferometry keratometry measurements in phakic eyes. Can J Ophthalmol 2009;44(6):700-704. [CrossRef]
[PubMed]
11 Dinc U, Gorgun E, Oncel B, Yenerel M, Alimgil L.
Assessment of anterior chamber depth using Visante optical coherence
tomography, slitlamp optical coherence tomography, IOL Master, Pentacam and
Orbscan IIz. Ophthalmologica
2010;224(6):341-346. [CrossRef] [PubMed]
12 Elbaz U, Barkana Y, Gerber Y, Avni I, Zadok D.
Comparison of different techniques of anterior chamber depth and keratometric
measurements. Am J Ophthalmol
2007;143(1):48-53. [CrossRef] [PubMed]
13 Szalai E, Berta A, Németh G, Hassan Z, Módis LJ.
Anterior chamber depth measurements obtained with Pentacam HR® imaging system
and conventional A-scan ultrasound. Ophthalmic
Surg Lasers Imaging 2011;42(3):248-253. [CrossRef] [PubMed]
14 Gursoy H, Sahin A, Basmak H, Ozer A, Yildirim N,
Colak E. Lenstar versus ultrasound for ocular biometry in a pediatric
population. Optom Vis Sci
2011;88(8):912-919. [CrossRef] [PubMed]
15 Lee J, Kim J, Kim H, Song J. Comparison of
anterior chamber depth measurement between Orbscan IIz and ultrasound
biomicroscopy. J Refract Surg
2007;23(5):487-491. [PubMed]
16 Zhang Q, Jin W, Wang Q. Repeatability,
reproducibility, and agreement of central anterior chamber depth measurements
in pseudophakic and phakic eyes: optical coherence tomography versus ultrasound
biomicroscopy. J Cataract Refract Surg
2010;36(6):941-946. [CrossRef] [PubMed]
17 Yazici A, Bozkurt E, Alagoz C, Alagoz N, Pekel G,
Kaya V, Yilmaz O. Central corneal thickness, anterior chamber depth, and pupil
diameter measurements using Visante OCT, Orbscan, and Pentacam. J Refract Surg 2010;26(2):127-133. [CrossRef] [PubMed]
18 Hashemi H, Mehravaran S. Corneal changes after
laser refractive surgery for myopia: comparison of Orbscan II and Pentacam
findings. J Cataract Refract Surg
2007;33(5):841-847. [CrossRef] [PubMed]
19 Utine C, Altin F, Cakir H, Perente I. Comparison
of anterior chamber depth measurements taken with the Pentacam, Orbscan IIz and
IOLMaster in myopic and emmetropic eyes. Acta
Ophthalmol 2009;87(4):386-391. [CrossRef] [PubMed]
20 Salouti R, Nowroozzadeh M, Zamani M, Ghoreyshi M,
Salouti R. Comparison of anterior chamber depth measurements using Galilei, HR
Pentacam, and Orbscan II. Optometry
2010;81(1):35-39. [CrossRef] [PubMed]
21 O’Donnell C, Hartwig A, Radhakrishnan H.
Comparison of central corneal thickness and anterior chamber depth measured
using LenStar LS900, Pentacam, and Visante AS-OCT. Cornea 2012;31(9):983-988. [CrossRef] [PubMed]
22 Huang J, Pesudovs K, Wen D, Chen S, Wright T,
Wang X, Li Y, Wang Q. Comparison of anterior segment measurements with rotating
Scheimpflug photography and partial coherence reflectometry. J Cataract Refract Surg
2011;37(2):341-348. [CrossRef] [PubMed]
23 Domínguez-Vicent A, Monsálvez-Romín D, AJ A-C,
García-Lázaro S, Montés-Micó R. Measurements of anterior chamber depth,
white-to-white distance, anterior chamber angle, and pupil diameter using two
Scheimpflug imaging devices. Arq Bras
Oftalmol 2014;77(4):233-237. [CrossRef] [PubMed]
24 Németh G, Hassan Z, Módis LJ, Szalai E, Katona K,
Berta A. Comparison of anterior chamber depth measurements conducted with
Pentacam HR® and IOLMaster®. Ophthalmic
Surg Lasers Imaging 2011;42(2):144-147. [PubMed]
25 Lavanya R, Teo L, Friedman D, Aung H, Baskaran M,
Gao H, Alfred T, Seah S, Kashiwagi K, Foster P, Aung T. Comparison of anterior
chamber depth measurements using the IOLMaster, scanning peripheral anterior
chamber depth analyser, and anterior segment optical coherence tomography. Br J Ophthalmol 2007;91(8):1023-1026. [CrossRef]
[PubMed] [PMC free article]
26 Rozema J, Wouters K, Mathysen D, Tassignon M.
Overview of the repeatability, reproducibility, and agreement of the biometry
values provided by various ophthalmic devices. Am J Ophthalmol 2014;158(6):1111-1120. [CrossRef] [PubMed]
27 McAlinden C, Khadka J, Pesudovs K. Statistical
methods for conducting agreement (comparison of clinical tests) and precision
(repeatability or reproducibility) studies in optometry and ophthalmology. Ophthal Physiol Opt 2011;31(4):330-338.
[CrossRef] [PubMed]
28 Food and Drug Administration, Division of
Ophthalmic Devices. Intraocular lens guide document. In,
http://www.fda.gov/ohrms/dockets/98fr/994052gd.pdf
29 Bland J, Altman D. Statistical methods for
assessing agreement between two methods of clinical measurement. Lancet 1986;8(1):307-310. [CrossRef]
30 Cairns G, McGhee C. Orbscan computerized
topography: attributes, applications, and limitations. J Cataract Refract Surg 2005;31(1):205-220. [CrossRef] [PubMed]
31 Kim S, Kim H, Song J. Comparison of internal
anterior chamber diameter imaging modalities: 35-MHz ultrasound biomicroscopy,
Visante optical coherence tomography, and Pentacam. J Refract Surg 2010;26(2):120-126. [CrossRef] [PubMed]
32 Kohnen T, Thomala M, Cichocki M, Strenger A.
Internal anterior chamber diameter using optical coherence tomography compared
with white-to-white distances using automated measurements. J Cataract Refract Surg
2006;32(1):1809-1813. [CrossRef] [PubMed]
33 Montés-Micó R, Carones F, Buttacchio A,
Ferrer-Blasco T, Madrid-Costa D. Comparison of immersion ultrasound, partial
coherence interferometry, and low coherence reflectometry for ocular biometry
in cataract patients. J Refract Surg
2011;27(9):665-671.<bb> [CrossRef] [PubMed]
[Top]