Download Changes in anterior chamber depth during accommodation: a pilot

ARTICLE
Changes in anterior chamber depth during
accommodation: a pilot study
Antonio J. Del Águila-Carrasco, MSc; Alberto Domínguez-Vicent, MSc; Daniel Monsálvez-Romín,
OD; Cari Pérez-Vives, MSc; Vicent Sanchis, MSc
PURPOSE: To study anterior chamber depth (ACD) behaviour in different positions, with
different degrees of accommodation.
SETTING: Academic department associated to a regional hospital.
METHODS: ACD data were acquired from 20 young, healthy subjects under 8 different
vergences, from +2 dioptres (D) to –5 D using a Pentacam HR device. Measurements were
taken for the central zone of the ACD and for 4 more positions, each in a different direction
(superior, inferior, nasal and temporal), 2 mm from the centre.
RESULTS: Changes in each position of the ACD resulting from accommodation were
small and generally insignificant (P > 0.05). The statistically deepest ACD value for all
vergences was found at the central position. The superior-nasal and temporal-inferior pairs
did not show statistically significant differences (P > 0.05) for all vergences. In addition,
temporal and inferior chamber depths were statistically significantly deeper (P < 0.05) than
superior and nasal chamber depths.
CONCLUSIONS: While the central position presents the deepest ACD, the superiornasal pair presents the narrowest ACD. No significant changes in ACD occur after 5 D of
accommodation.
J Emmetropia 2013; 4: 87-91
Submitted: 02/26/2013
Revised: 03/11/2013
Accepted: 03/13/2013
Optometry Research Group (GIO), Department of Optics.
University of Valencia. Spain.
Acknowledgements: 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), by a
Atracció de Talent research scholarship (Universidad de Valencia)
awarded to Alberto Domínguez Vicent, by a collaboration
scholarship (Ministerio de Educación, Ciencia y Deporte) awarded
to Daniel Molsálvez Romín and by a VALi+D research scholarship
(Generalitat Valenciana) awarded to Cari Pérez-Vives.
Financial disclosure: The authors have no proprietary interest in any
of the products or devices mentioned in this article.
Corresponding author: Antonio J. Del Águila-Carrasco
Department of Optics – University of Valencia
c/Dr. Moliner, 50 – 46100 – Burjassot – Spain
e-mail: [email protected]
© 2013 SECOIR
Sociedad Española de Cirugía Ocular Implanto-Refractiva
Many papers have been published on the changes
of different anatomical structures of the eye during
accommodation, such as anterior chamber depth
(ACD)1-4,6-14,16-28, anterior chamber angle (ACA)16, or
pupil diameter3,5,8,26,27. In these studies, it was observed
that the values of these anatomical structures decrease
after increasing the vergence of the fixation target (Figure
1 shows an example of changes in ACD as a function of
accommodation).
The issue with these studies is that all the ACD
measurements were taken only in the central zone,
without measuring changes in peripheral ACD during
accommodation. It would be interesting to determine
these changes, with the aim of developing new models
of intraocular lenses (IOLs) and improving on current
models. These new IOLs should protect the intraocular
anatomical structures, such as corneal endothelium,
iris or crystalline lens, from possible disorders or
disturbances caused by the contact of the lens with
ISSN: 2171-4703
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CHANGES IN ACD DURING ACCOMODATION
any of these structures after surgery. Additionally,
since accommodation could lead to changes in various
anatomical structures, it is important to study changes
in ACD at different levels of accommodation, and also
in different positions, not only the central zone. The
more that is known about the modifications that occur
in the eye while accommodating or when it is relaxed,
the better designed the IOLs will be. Consequently,
it will be easier to differentiate those subjects who are
candidates for IOL implantation from those who do not
have an appropriate ACD value in any determined zone.
The aim of the present study was to analyse changes
in central and peripheral ACD during accommodation.
To the authors’ best knowledge, this is the first report that
evaluates these ocular changes during accommodation.
PATIENTS AND METHODS
Subjects
Twenty right eyes from twenty individuals, 9 male
and 11 female, aged from 20 to 30 years (23.20 ± 1.68
years) were included in this study. Spherical refractive errors
ranged between –0.50 to +0.50 dioptres (D), the mean
spherical refractive error being 0.23 ± 0.28 D. They had clear
intraocular media and no known ocular disease. All patients
were informed about the details of this study, and written
informed consent was obtained after verbal and written
explanation of the nature and possible consequences of the
study, in accordance with the Declaration of Helsinki. No
Institutional Review Board approval was required for this
Figure 1. Changes in anterior chamber depth during accommodation in different positions of the anterior chamber.
study. Subjects with best-corrected visual acuity of less than
20/40, ocular or systemic disease, ocular surgery history,
intraocular pressure higher than 21 mmHg and presence
of retinal or optic disk disease, were excluded from taking
part in this study.
Pentacam HR
The Pentacam HR instrument uses a rotating
Scheimpflug camera for the non-invasive measurement
of the anterior segment (Figure 2). This camera calculates
a three-dimensional model of the anterior segment. The
system has two different three-dimensional modes: a
regular three-dimensional scan that takes 50 images in 2
seconds, and a special three-dimensional high-resolution
corneal mode, in which the camera takes 50 images in
1 second. The Pentacam automatically captures images
once correct alignment in the x, y, and z directions is
attained. After image capture, the instrument analyses the
50 Scheimpflug images of the anterior eye to reconstruct
the anterior segment, thus providing information about
corneal curvature (front and back surfaces), corneal
elevation (front and back corneal surfaces), pachymetry
maps and ACD information. The instrument generates a
quality setting reading for each measurement, providing
information on the reliability of each 3D scan. Studies
show that the Pentacam has excellent repeatability and
first-rate interobserver reproducibility for measuring
ACD15. Moreover, the Pentacam HR has a red LED
that can be used as a fixation target and moved in 0.5 D
steps from +2 D to –5 D. Before each measurement, the
subject was instructed to maintain the fixation target in
focus during the measurement.
Figure 2. Pentacam HR device connected to a computer.
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Experimental procedure
The Pentacam HR was used to automatically
measure central and peripheral ACD for far vision and
for different positions of the fixation target. The central
ACD was defined as the distance between the corneal
endothelium and the anterior surface of the crystalline
lens. The peripheral ACD was measured at 2 mm from
the centre of the cornea in nasal, temporal, superior
and inferior directions. For these four positions, the
ACD was measured as the distance between the corneal
endothelium and the iris. The resolution of these
measurements was 0.01 mm in both cases.
ACD was measured 3 times per eye, and the average
value was retained for all distances evaluated, ranging
from +2 D to –5 D in steps of 1 D. Before starting the
measurements, the volunteer had to fixate the target
for 2 seconds to allow an appropriate accommodation
response. During the measurements, the patient
was requested to not blink, to avoid affecting the
measurement. This procedure was performed during a
single session. The ACD was expressed in millimetres.
All measurements were carried out by the same specialist,
who did not know the objective of this study and had
experience using the Pentacam HR.
89
study was to compare results under different conditions
(accommodative stimulus and anatomical localisation),
the study design is factorial, so a repeated measures
ANOVA was used and the assumption of normality was
ensured by means of the Shapiro-Wilk test. A post-hoc
multiple comparison test using the Holm Sidak method
was performed when ANOVA revealed differences.
Statistical significance was set at P = 0.05.
RESULTS
Figure 3 shows the variation in ACD during
accommodation in the five different positions (central
position, and 2 mm in a nasal, temporal, inferior and
superior direction) where measurements were taken. A
small reduction in ACD occurred as accommodation
increased in all cases, but this reduction was not
statistically significant at any position of the anterior
chamber (P > 0.05). The results show that central position
gives the statistically deepest ACD for all vergences, while
the superior-nasal and temporal-inferior pairs were not
statistically significantly different (P = 0.056 and P =
0.225, respectively). Nevertheless, temporal and inferior
chamber depths were statistically significantly greater (P
< 0.05) than superior and nasal chamber depths.
Statistical analysis
After data collection, anterior chamber depth
measurements were exported from the instrument for
further analysis. Statistical analysis was performed using
SigmaPlot for Windows Version 11 (Systat Software,
GmbH; Erkrath, Germany). Since the main goal of the
DISCUSSION
The aim of this study was to evaluate the behaviour
of the ACD in different positions at different levels
of accommodation. The use of the Pentacam HR
device allowed us to perform the measurements in a
Figure 3. Comparison of the anterior chamber depth from a subject with relaxed accommodation (above), and the ACD from the same subject
when the level of accommodation is set at –5 D (below). Note the slight decrease in the ACD when the level of accommodation increases.
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CHANGES IN ACD DURING ACCOMODATION
non-invasive way. Figure 3 shows the decrease in ACD
when accommodation is increased. This happens at the
five positions analysed. However, these changes were
small and no statistically significant differences were
found for the positions evaluated. This indicates that
there is practically no modification of the ACD during
accommodation. Our results are similar to those obtained
previously10,11,17,22,24,27, in which the mean ACD change
after accommodation was about 0.1 mm. However,
these results contradict those of Du et al.7, where the
mean ACD change was 0.17 mm. This difference may
be because the cited report studied changes in ACD after
pharmacological accommodation.
In Figure 3, ACD appears to vary considerably for
each position of measurement within the same degree
of accommodation (same fixation object vergence). For
the same level of accommodation, our results revealed
statistically significant differences between the ACD
for all positions, except for the inferior and temporal
positions (no differences), and superior and nasal
positions (no differences either), indicating that the
anterior chamber shows variations in depth that are not
negligible. It is important to take this into consideration
before IOL implantation (angle-supported anterior
chamber lenses, iris-fixated lenses, etc.), or for checking
already implanted IOLs for possible post-surgery
problems. It is extremely important that the intraocular
lens does not make contact with any anatomical
structure of the eye, in order to prevent disturbances
or disorders in the corneal endothelium, the iris, the
crystalline, or in the anterior chamber itself. For this
reason, it is essential to know as much as possible about
the anterior chamber. ACD measurements in different
positions before surgery are useful for preventing these
disturbances, and also for designing new IOLs or
improving those that are currently available. It is fair
to mention the limitations of this study, such as the
number of eyes measured, the fact that we only used
one device to measure ACD and also that a small age
range was included.
In summary, although there are practically no
changes in ACD during accommodation, this parameter
changes appreciably depending on the position where
the measurement has been taken. This is an important
factor in the design and implantation of IOLs.
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First author:
Antonio J. Del Águila-Carrasco
Optometry Research Group (GIO),
Department of Optics. University of Valencia. Spain.