Biometry of Anterior Segment of Human Eye on Both
Horizontal and Vertical Meridians during
Accommodation Imaged with Extended Scan Depth
Optical Coherence Tomography
Lin Leng
.
, Yimin Yuan
.
, Qi Chen, Meixiao Shen, Qingkai Ma, Beibei Lin, Dexi Zhu, Jia Qu, Fan Lu*
School of Ophthalmology and Optometry, Wenzhou Medical University, Wenzhou, Zhejiang, China
Abstract
Purpose:
To determine the biometry of anterior segment dimensions of the human eye on both horizontal and vertical
meridians with extended scan depth optical coherence tomography (OCT) during accommodation.
Methods:
Twenty pre-presbyopic volunteers, aged between 24 and 30, were recruited. The ocular anterior segment of each
subject was imaged using an extended scan depth OCT under non- and 3.0 diopters (D) of accommodative demands on
both horizontal and vertical meridians. All the images were analyzed to yield the following parameters: pupil diameter (PD),
anterior chamber depth (ACD), anterior and posterior surface curvatures of the crystalline lens (ASC and PSC) and the lens
thickness (LT). Two consecutive measurements were performed to assess the repeatability and reproducibility of this OCT.
They were evaluated by calculating the within-subject standard deviation (SD), a paired t-test, intra-class correlation
coefficients (ICC) and the coefficient of repeatability/reproducibility (CoR).
Results:
There were no significant differences between two consecutive measurements on either horizontal or vertical
meridians under both two different accommodative statuses (P.0.05). The ICC for all parameters ranged from 0.775 to
0.998, except for the PSC (0.550) on the horizontal meridian under the non-accommodative status. In addition, the CoR for
most of the parameters were excellent (0.004% to 4.89%). In all the parameters, only PD and PSC were found different
between the horizontal and vertical meridians under both accommodative statuses (P,0.05). PD, ACD, ASC and PSC under
accommodative status were significantly smaller than those under the non-accommodative status, except that the PSC at
the vertical meridian did not change. In addition, LT was significantly increased when accommodation.
Conclusion:
The extended scan depth OCT suc cessfully measured the dimensions of the anterior eye du ring
accommodation with good repeatability and reproducibility on both horizontal and vertical meridians. The asymmetry
of lens posterior surface and oval-shaped pupil were found during accommodation.
Citation: Leng L, Yuan Y, Chen Q, Shen M, Ma Q, et al. (2014) Biometry of Anterior Segment of Human Eye on Both Horizontal and Vertical Meridians during
Accommodation Imaged with Extended Scan Depth Optical Coherence Tomography. PLoS ONE 9(8): e104775. doi:10.1371/journal.pone.0104775
Editor: Andreas Wedrich, Medical University Graz, Austria
Received February 20, 2014; Accepted July 14, 2014; Published August 12, 2014
Copyright: ß 2014 Leng et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provide d the original author and source are credited.
Funding: This work was supported by National Natural Science Foundation of China (Grant No. 81170869 to Lu; Grant No. 81200672 to Chen), Wenzhou Science
and Technology program (Grant No. Y20120151 to Chen), and National Basic Research Program (973 Program) of China (2011CB504601). The funders had no role
in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* Email: lufan62@mail.eye.ac.cn
. These authors contributed equally to this work.
Introduction
Accommodation is the ability of the eye to change the refractive
power to focus on the objects at different distances, which is
controlled by ciliary muscle contraction. [1] Among all the
accommodation theories, the Helmholtzian theory is the most
widely accepted. [2] In order to allow the retina to focus on objects
at near distances with clarity, the ciliary muscle contracts, zonular
fibres relax, causing the thickness, curvature and position of the
crystalline lens to change. [3,4] Rohen JW. et al. used the
anatomical method to confirm this theory and further explained
the process of accommodation. [5].
However, the ability of accommodation decreases gradually as
age increases. [6] The inevitable decline in accommodative
amplitude and characteristic loss of near visual function with age
causes presbyopia. Although the occurrence and development of
presbyopia is not entirely clear, the most recent evidence suggests
that lenticular processes are of key significance. [7] The previous
study focuses on the changes of the ocular diopter, but this is not
enough to fully understand the entire accommodative system. [8,9]
During the ocular accommodation, the shape and position of the
crystalline lens changes, and this was considered to be the most
important factor in the power change of the ocular optical system.
In addition, changes in the pupil diameter and the anterior
chamber dimensions also play an indispensable role in accommo-
PLOS ONE | www.plosone.org 1 August 2014 | Volume 9 | Issue 8 | e104775
dation. Therefore, it is essential to investigate the dynamic
variations of the anterior segment configuration dimensions in
understanding the characteristics of the ocular accommodation.
Recently, several techniques have been developed for measuring
the anterior segment of the eye in vivo, such as the slitlamp
assessment, [10] Scheimpflug imaging, [7,11] A scan ultra-
sounds,[12] ultrasound biomicroscopy (UBM), [13] and Purkinje
reflexes. [14] However, the slitlamp method is entirely subjective,
and measurements can therefore vary between examiners.
Rotating Scheimpflug images are not corrected for optical
distortion and their resolution is relatively low. A scan ultrasound
and UBM are both invasive methods and can affect the
morphology of the anterior chamber. The Purkinje reflexes
cannot directly reflect the ocular optic configuration dimensions.
Optical coherence tomography (OCT) has been widely
recognized as a rapid, non-invasive and precise technology for
biometric measurements at present. [15–17] In our previous study,
an extended scan depth spectral domain OCT (SD-OCT) was
verified to be a potential method in quantifying changes in the
anterior segment dimensions on the horizontal meridian during
accommodation. [18] However, the information of the vertical
meridian was not mentioned. The goals of this study are to
determine the repeatability and reproducibility of this SD-OCT in
measuring the anterior segment on both the horizontal and
vertical meridians, and to compare the differences of the anterior
segment dimensions between the two meridians during the non-
and 3.0 diopters (D)-accommodative statuses.
Materials and Methods
Subjects
Twenty prepresbyopic volunteers (9 female and 11 male) were
recruited from Wenzhou Medical University, with a mean age 6
standard deviation of 25.9562.31 years. The mean spherical
equivalent of the subjects was 20.4260.29 D. None of the
subjects had a history of ocular or systemic disease or surgery. This
study was approved by the Office of Research Ethics, Wenzhou
Medical University.
Written informed consent was obtained from each subject, and
all procedures were performed according to the Declaration of
Helsinki requirements for research involving human subjects.
Instruments
Extended scan depth SD-OCT was used to image the ocular
anterior segment, which has been previously detailed. [18,19] In
brief, the center wavelength of the super luminescent diode-based
light source (Inphenix, IPSDD0808, Livermore, CA) was 840 nm,
with a bandwidth of 50 nm. The axial resolution of the system in
the eye was approximately 7.5
mm. An extended depth range of
7.8 mm in air was achieved by a custom spectrometer. The total
exposure power was less than 1.00 mW, and within the safe range
for the human eye, according to ANSI Z136.1. [20].
Measurements
The experimental procedures for each subject were arranged
after 10:00AM. Trial lenses were set in front of the left eye of each
subject, who were each viewing a target at a non-accommodative
and 3.0 D of accommodative demands successively. The right eye
was imaged with the SD-OCT by an experienced operator
(Fig. 1). For each subject, both horizontal and vertical meridians
were taken twice under two different accommodative statuses. A
Matlab program was developed for image correction and
processing on the RAW OCT images to yield dimensional
parameters of the anterior segment of the eye. In total, five
anterior segment parameters were obtained with the post-process
constructed images in the horizontal and vertical meridians,
respectively (Fig. 2). They included pupil diameter (PD), anterior
chamber depth (ACD), anterior and posterior surface curvatures
of crystalline lens (ASC and PSC), and crystalline lens thickness
(LT). As shown in Fig. 3, the anterior segment changed from the
non-accommodative status to the 3.0 D-accommodative status.
Statistical Analysis
Statistical analysis was performed using SPSS for Microsoft
Windows (version 18.0, SPSS, Inc.). Results were presented as the
mean 6 SD. Paired t-tests were used to compare the intra-subject
repeatability. All statistical tests were two-tailed. If the P values
were less than 0.05, the results were considered statistically
significant. Intra-class Correlation Coefficient (ICC) is a measure
of correlation for data of repeated measurements. Coefficient of
reproducibility (CoR) takes into account the impact of random
and/or systematic errors on reproducibility, where the result of
reproducibility is more reliable when the CoR is smaller.
Results
Comparisons of the anterior segment dimensions between the
horizontal and vertical meridians during the non-accommodative
and 3.0 D-accommodative statuses (Table 1) were revealed. There
were significant differences of PD and PSC between the horizontal
and vertical meridians under both statuses (P,0.05).
Reproducibility and repeatability of five anterior segment
parameters were determined under the different conditions
(Table 2). Of all the parameters, there is no statistically significant
difference between two repeated measurements on either meridian
under different accommodative statuses (P.0.05). The ICC for all
parameters ranged from 0.775 to 0.998, except for PSC (0.550) on
the horizontal meridian under the non-accommodative status.
The CoR for most of the parameters were presented (0.004% to
4.89%). However, the CoR for ASC (9.50%) and PSC (8.16%) on
the horizontal meridian under 3.0 D-accommodative status, and
ASC (5.79%) and PSC (6.78%) on the vertical meridian under the
non-accommodative status were relatively high.
The values of PD, ACD, ASC and PSC on both meridians
under the accommodative statues (Table 1) were significantly
smaller than those under the non-accommodative status (P,0.05),
except that the PSC did not change on the vertical meridian (P.
0.05). In addition, the LT was significantly increased with
accommodation (P,0.05).
Discussion
Optical coherence tomography is a new imaging instrument
based on the optical interference principle. Izatt JA. et al. [21] took
advantage of OCT to image the anterior segment for the first time
in 1994. OCT probes biological tissue backscatter and reflection
from the incident light. With this optical interferometric imaging
principle, OCT has the advantage of high resolution, fast imaging
and noninvasive biopsy-like qualities. Owing to its long scan
depth, SD-OCT was used to image the full-range of ocular
anterior segments in the present study. Not only can it clearly show
the structure of the anterior chamber and pathological changes,
but it can also be used to make quantitative analysis. [22,23]
Dimensional parameters of the two accommodative statuses from
two meridianal measurement showed good reproducibility and
repeatability.
In previous studies, several imaging technologies have been used
to quantify the dimensions of ocular anterior segment. Tsorbatzo-
Biometry of Anterior Segment of Human Eye during Accommodation
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Figure 1. Diagram of the fixation target system. A 1.2 m long optical rail was installed upon a lift table, and placed beside the slit lamp, fixed by
a Philips 17-inch LCD monitor on a slider for displaying the target. This LCD monitor was able to move along the optical rail to adjust the distance
between the visual target and the human eye, to induce a different stimulus of accommodation. In order to allow the subjects to fix on the target,
without being affected by the moving probe, a plane mirror was installed on the slit lamp column, so that the target was projected into the eye after
specular reflection.
doi:10.1371/journal.pone.0104775.g001
Figure 2. OCT images of ocular anterior segment on horizontal (A) and vertical (B) meridians. The values of dimensional parameters were
obtained from the images using custom software. Anterior chamber depth (ACD) and lens thickness (LT) were measured along the perpendicular line.
Pupil diameter (PD) was measured along the horizontal line from both ends of the iris. The radii of anterior and posterior surface curvatures of the
crystalline lens (ASC/PSC) were measured from the two surfaces of the lens.
doi:10.1371/journal.pone.0104775.g002
Biometry of Anterior Segment of Human Eye during Accommodation
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Figure 3. The comparison of OCT images obtained before (left) and after (right) accommodation on horizontal and vertical
meridians.
doi:10.1371/journal.pone.0104775.g003
Table 1. Anterior Segment Dimensions at the Horizontal and Vertical Meridians during accommodation.
Variables(mm)
Non-accommodative Status 3.0D-Accommodative Status
Horizontal Meridian Vertical Meridian Horizontal Meridian Vertical Meridian
PD
a
5.3960.75 5.6660.78
*
4.8460.94 5.3760.68
*
PD
b
5.3860.83 5.7160.67
*
4.8560.94 5.3960.66
*
Diff 20.0160.01 0.0660.07 0.0060.01 0.0260.04
ACD
a
3.1560.26 3.1860.27 3.0560.25 3.0660.27
ACD
b
3.1660.26 3.1860.27 3.0660.26 3.0760.29
Diff 0.0160.01 0.0160.10 0.0160.02 0.0160.04
ASC
a
12.2161.38 11.9961.64 10.2761.16 10.4860.93
ASC
b
12.0561.44 11.8161.09 10.5361.42 10.4560.95
Diff 20.1760.06 20.1560.69 0.2760.99 20.0260.01
PSC
a
5.6260.72 6.1260.62
*
5.2860.56 5.8760.55
*#
PSC
b
5.6560.46 5.9560.56
*
5.4160.44 5.9460.54
*#
Diff 0.0360.18 20.1660.41 0.1360.44 0.0760.29
LT
a
3.7760.18 3.7860.17 3.8960.17 3.8960.17
LT
b
3.7760.19 3.8060.18 3.8860.18 3.9060.18
Diff 0.0060.01 0.0260.01 20.0160.00 0.0060.00
a
Mean 6 SD for the first measurement of the eye.
b
Mean 6 SD for the second measurement of the eye.
* Statistically significance of the parameters between the two meridians (P,0.05).
#
No statistically significance of the parameters during accommodation (P.0.05).
There was no statistical significance of any of the parameters between the two repeated measurements at either meridian under different accommodative statuses (P.
0.05).
PD, pupil diameter; ACD, anterior chamber depth; ASC, anterior surface curvature of crystalline lens; PSC, posterior surface curvature of crystalline lens; LT, crystalline
lens thickness; Diff, difference between two repeated measurements.
doi:10.1371/journal.pone.0104775.t001
Biometry of Anterior Segment of Human Eye during Accommodation
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gulou, A. et al. [24] indicated that the lens thickness and anterior
chamber depth were 3.77660.188 mm and 3.57860.278 mm,
respectively using a partial coherence interferometry. Yan, PS. et
al. [25] reported 4.5660.86 mm of pupil diameter and
3.7960.22 mm of anterior chamber depth with a slit-lamp
OCT. Using Scheimpflug imaging technology, Rosales, P. et al.
[26] measured ACD, LT, ASC and PSC and gave averaged values
of 2.86 mm, 4.06 mm, 10.37 mm, and 5.55 mm, respectively.
Hermans, EA. et al. [27] reported that the ASC and PSC were
11.4561.7 mm and 6.1161.4 mm, respectively using MRI. Ortiz
S.et al. [28] took advantage of three-dimensional (3D) OCT
imaging to present that the values of ASC (ranged from 10.27 to
14.14 mm) and PSC (ranged from 6.12 to 7.54 mm). The anterior
segment parameters at the horizontal or vertical meridians
including ACD, PD, LT and the radii of both surface curvatures
of the lens were consistent with previous studies with subjects of
comparable age and refractive statuses.
However, in most of previous studies, only one meridian of the
anterior eye was imaged. The dimensional parameters of anterior
eye were always presented by an average value. In addition, few
literatures investigated the dimensional changes of anterior eye
during accommodation. This may be due to the technical
limitation of imaging methods. OCT is a rapid and non-invasive
method with micrometer-scale resolution, and is a suitable tool for
investigate the morphology of anterior eye with accommodation.
[18] In the present study, we compared the parameters between
vertical and horizontal meridians, and did find that there were
significant differences in PD and PSC between the two meridians.
To the best of our knowledge, this may be the first time assessing
the differences in ocular dimensional parameters between vertical
and horizontal meridians during accommodation. We suppose
these differences should be considered in future studies on
accommodation mechanism and visual function.
For instance, significant differences were found in PD between
vertical and horizontal meridians. This indicated that the pupil is
vertical oval shaped during accommodation. [29–30] Thus, if we
want to study the effect of pupil on the ocular wavefront
aberrations or refractive surgery, pupil area, rather than pupil
diameter, may be a more acceptable parameter to represent the
pupil size.
Significant differences were found in PSC between the two
meridians. The values of ASC and PSC have been measured by
several methods both in vivo, [26,31] and in vitro, [32,33] and
similar results were reported. For instance, Chien CH. et al. [34]
made use of polar coordinates and found a parameterization with
cosines to prove it to be the most suitable for the human lens
surface. Kasprzak HT. et al. [35] proposed an analytical function
that describes the complete axisymmetric lens profile in two
different accommodative statuses. Hermans, EA. et al. [27]
calculated the mean surface area based on eight parts of the lens,
measured with 3D MRI, and confirmed the non-symmetric
properties of the human lens. Ortiz S. et al. [28] verified lens
surfaces to be fitted by biconicoids and Zernike polynomials. Our
finding indicated the asymmetry of the posterior surface of the
lens, however, this was not found to be true of the anterior surface.
This may be due to the growing up of the lens during human’s life.
Rosen AM. et al. [32] proposed that the anterior part of the lens
grows more slowly than the posterior surface. It is possible that
with gravity, the down-deposition of the lenticular cells may result
in the differences between horizontal and vertical curvatures of the
lens.
In the present study, the OCT scans were performed across the
corneal apex. However, the lens may tilt and become decentered
since it is located in the aqueous humor. Thus it is possible that the
apex of lens surface was not captured during OCT imaging. This
may explain why the CoRs of ASC and PSC were slightly bigger
compared to other parameters. In our future studies, three-
dimensional OCT scan is proposed to obtain reconstructed 3D
image of the lens. Thus the apex of lens surface can be identified
and the radius of lens surface can be calculated more accurately.
In conclusion, the extended scan depth OCT successfully
measured the dimensions of the anterior eye in both non-
accommodative and accommodative statuses. Good repeatability
and reproducibility were presented at both horizontal and vertical
meridians. The asymmetry of the posterior surface of the lens and
oval-shaped pupil were found during accommodation.
Author Contributions
Performed the experiments: LL YY QC BL. Analyzed the data: LL YY
MS. Contributed reagents/materials/analysis tools: MS QM DZ JQ FL.
Wrote the manuscript: LL YY.
Table 2. Repeated Measurements of the Anterior Segment Dimensions.
PD ACD ASC PSC LT
H-0.0D
a
CoR(%) 0.235 0.387 0.460 3.273 0.224
ICC 0.979 0.997 0.927 0.550 0.976
V-0.0D
a
CoR(%) 1.259 3.108 5.793 6.779 0.185
ICC 0.973 0.987 0.841 0.850 0.987
H-3.0D
b
CoR(%) 0.299 0.618 9.502 8.163 0.046
ICC 0.997 0.998 0.858 0.887 0.991
V-3.0D
b
CoR(%) 0.712 1.279 0.087 4.885 0.004
ICC 0.998 0.998 0.775 0.881 0.997
a
Repeatability of the variables obtained from two repeated measurements at either meridian in non-accommadative status.
b
Repeatability of the variables obtained from two repeated measurements at either meridian in 3.0 D-accommadative status.
PD, pupil diameter; ACD, anterior chamber depth; ASC, anterior surface curvature of crystalline lens; PSC, posterior surface curvature of crystalline lens; LT, crystalline
lens thickness; H, horizontal meridian; V, vertical meridian; CoR, coefficient of repeatability; ICC, intra-class correlation coefficient.
doi:10.1371/journal.pone.0104775.t002
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