Research Article
Repeatability of Aberrometry-Based Automated Subjective
Refraction in Healthy and Keratoconus Subjects

Gonzalo Carracedo , Carlos Carpena-Torres , Cristina Pastrana, Ana Privado-Aroco,
Marı́a Serramito, and Laura Batres

Department of Optometry and Vision, Faculty of Optics and Optometry, Complutense University of Madrid, Madrid, Spain

Correspondence should be addressed to Gonzalo Carracedo; jgcarrac@ucm.es

Received 7 July 2020; Revised 13 October 2020; Accepted 19 October 2020; Published 30 October 2020

Academic Editor: Carlo Cagini

Copyright © 2020 Gonzalo Carracedo et al. (is is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is
properly cited.

Purpose. To compare the intersession repeatability of the Eye Refract, a new instrument to perform aberrometry-based automated
subjective refraction, on healthy and keratoconus subjects. Materials and Methods. A cross-sectional and randomized study was
performed. A total of 64 participants were evaluated in the study, selecting one eye per participant randomly. (e sample was
divided into two different groups: 33 healthy subjects (38.85± 13.21 years) and 31 with keratoconus (37.29± 11.37 years). (ree
refractions per participant with the Eye Refract were performed on three different days, without cycloplegia. (e repeatability
analysis of refractive variables (M, J0, and J45), binocular corrected distance visual acuity (BCDVA), and spent time in refraction
was performed in terms of repeatability (Sr), its 95% confidence interval (r), and intraclass correlation coefficient (ICC). Results.
(ere were no statistically significant differences (P≥ 0.05) between sessions in both groups for all refractive variables (M, J0, and
J45) and BCDVA. Spent time in refraction was reduced as the sessions went by (P< 0.05).(e Eye Refract was more repeatable for
refractive errors assessment in healthy subjects (M : Sr � 0.27 D; J0 : Sr � 0.09 D; J45 : Sr � 0.06 D) compared to those with ker-
atoconus (M : Sr � 0.65 D; J0 : Sr � 0.29 D; J45 : Sr � 0.24 D), while it was similar for BCDVA. Conclusions. (e Eye Refract offered
better repeatability to assess refractive errors in healthy subjects compared to those with keratoconus. Despite measurements
being also consistent in keratoconus subjects, they should be treated with caution in clinical practice.

1. Introduction

Refraction is probably the most frequent measurement in
clinical practice. Subjective refraction is considered the gold
standard procedure since it considers both optical and
neural aspects of vision [1].

Despite autorefractors allowing us to obtain previous
objective refraction as a reference to facilitate subjective
refraction, their main limitation is an overestimation of
myopia or underestimation of hyperopia [2–9]. Due to the
impossibility of using autorefractors to perform accurate
and precise refraction as the gold standard, new devices are
being developed to perform automated subjective refrac-
tion [10–15]. (e purpose of these devices is to use an
automated algorithm controlled by software to make a
subjective adjustment of refraction based on previous

objective refraction obtained from autorefraction. (ere-
fore, it is possible to incorporate both objective and sub-
jective refractions into a single instrument.

Currently, the Eye Refract system (Luneau Technology;
Chartres, France) is the only commercially available in-
strument to perform automated subjective refraction [14]. It
incorporates a binocular open-field aberrometer that mea-
sures objective refraction and a phoropter for subjective
adjustment of final prescription. Two of these commercially
available instruments in the past are no longer distributed
[10, 11, 13].

(e accuracy and precision of the Eye Refract to estimate
refractive errors has been confirmed in healthy subjects
[14, 16]. However, its repeatability to perform automated
subjective refraction is still unknown in healthy subjects and
other ocular conditions. For this reason, the purpose of the

Hindawi
Journal of Ophthalmology
Volume 2020, Article ID 4831298, 7 pages
https://doi.org/10.1155/2020/4831298

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https://doi.org/10.1155/2020/4831298


current study was to compare the intersession repeatability
of the Eye Refract to perform aberrometry-based automated
subjective refraction between healthy and keratoconus
subjects. (e repeatability analysis was performed for re-
fractive variables, visual acuity, and spent time in refraction.

2. Material and Methods

2.1. Design of the Study. A cross-sectional and randomized
study was conducted in compliance with good clinical
practices, institutional review board regulation, and fol-
lowing the tenets of the Declaration of Helsinki [17]. All the
participants were voluntarily involved in the study after
signing a written consent form, where the purpose and the
procedures of the study were explained. (e participants
were free to leave the study at any time. All the trials were
carried out at the University Clinic of Optometry of the
Complutense University of Madrid (Spain). (e Ethics
Committee of the Hospital Cĺınico San Carlos (Madrid,
Spain) approved the performance of the study (code 18/
458_R_P).

For each participant, three refractions were performed
with the Eye Refract by a single optometrist, without using
cycloplegia. (e refractions were performed on three dif-
ferent days, during a maximum period of two weeks,
depending on the availability of the participants. (e in-
tersession repeatability of the Eye Refract was evaluated for
refractive variables (M, J0, and J45), binocular corrected
distance visual acuity (BCDVA), and spent time in
refraction.

2.2. Sample. A total of 64 participants were evaluated in the
study, selecting one eye per participant randomly (flipping a
coin). (e sample was divided into two different groups: 33
healthy subjects (38.85± 13.21 years) and 31 with kerato-
conus (37.29± 11.37 years). (eir demographic character-
istics are detailed in Table 1.

(e recruitment was carried out to obtain a heteroge-
neous sample in both groups, whose inclusion and exclusion
criteria are detailed in Table 2.

2.3.EyeRefractSystem. (eEye Refract system is a binocular
aberrometer combined with a phoropter that performs an
aberrometry-based automated subjective refraction (Fig-
ure 1). First, the Eye Refract measures the objective re-
fraction from which a subjective adjustment is performed to
obtain the final prescription. All these refraction procedures
are based on an automated algorithm of the Eye Refract,
which is controlled with a digital tablet connected to the
system.

Following the manufacturer’s instructions, the partici-
pants were asked to put their chin and forehead on the
supports for this purpose and to look ahead to the fixation
image of the digital screen placed at 4m distance. At this
stage, aberrometry was measured in both eyes at the same
time with two Hartmann–Shack sensors. (ese sensors use a
near-infrared light of 800 nm, while the pitch of their
microlens array of these sensors is 0.1mm. To calculate the

objective refraction, the Eye Refract considers the wavefront
metric based on the principle of equivalent quadratic, using
the method of paraxial curvature matching proposed by
(ibos et al. [18]. (is metric considers the Zernike coef-
ficients C0

2 and C0
4 for M determination, C2

2 and C2
4 for J0

determination, and C−2
2 and C−2

4 for J45 determination.(e
Eye Refract measures the aberrations under physiological
pupil size, and it recalculates the values for a pupil size of
3mm. If the pupil size is inferior to 3mm, it provides the
values for physiological pupil size.

Once objective refraction was measured, the optometrist
asked the participants a series of questions provided by the
automated algorithm of the Eye Refract to adjust the final
prescription. (ese questions consisted of comparing two
spherical or cylindrical lenses, through the “lens 1 or lens 2”
method, and the refraction was modified based on their
answers until obtaining the final prescription in both eyes.

2.4. Analysis of Refractive Variables. (e refractive variables
were measured in terms of spherical equivalent (M), and
both vertical and oblique cylindrical vectors (J0 and J45),
based on the method proposed by (ibos et al. [19]. (e
following formulae were used for the calculations:

M � sphere + (cylinder/2)
J0 � −(cylinder/2)× cos (2 x axis)
J45� −(cylinder/2)× sin (2 x axis)

2.5. Measurement of Visual Acuity and Spent Time in
Refraction. Since the Eye Refract is a binocular instrument,
BCDVA was measured after finishing each refraction.
BCDVA was measured through the ocular of the Eye Re-
fract, using the high-contrast (100%) ETDRS chart of the
digital screen of the system placed at 4m distance.

On the other hand, the spent time in refraction was
measured with a timer. (e time was measured from the
start of the objective refraction with the Hartmann–Shack
sensors to the final measurement of BCDVA.

2.6. Statistical Analysis. (e sample size calculations were
performed using the Granmo 6.0 software (Institut Mu-
nicipal d’Investigació Mèdica; Barcelona, Spain), consider-
ing the refractive variables as the main ones. An alpha risk of
0.05 and a beta risk of 0.2 in a two-sided test were accepted.
(irty-two eyes were necessary for both groups to recognize
as a statistically significant difference greater than or equal to
0.25 D. (e common standard deviation was assumed to be
0.50 D.

(e statistical analysis was performed using the SPSS
Statistics 23 software (IBM; Chicago, Illinois, USA). (e
intersession repeatability analysis was performed consid-
ering the following statistical variables: repeatability (Sr), its
95% confidence interval (r), the mean difference between
sessions (bias), and its standard deviation (SD). Sr is
mathematically defined as the square root of the mean
square within-subject standard deviation. r is mathemati-
cally defined as 2.77× Sr, and it represents the limit value

2 Journal of Ophthalmology



within which 95% of differences between sessions should be
[20]. Additionally, the intraclass correlation coefficient
(ICC), which represents the degree of agreement between
the three repeated measurements, was calculated. According
to McGraw and Wong convention [21], ICC analysis was
performed using a model of one-way random effects for
single measurements.

(e normal distribution of all the variables was assessed
using the Shapiro–Wilk test. Once the normal distribution of
all the variables was confirmed, the one-way analysis of
variance (ANOVA) for related samples with Bonferroni
correction was performed to check the statistical differences
between sessions. A statistical significance of 95% (P< 0.05)
was established.

3. Results

Table 3 summarizes the values of all the variables under
study obtained with the Eye Refract in each session and its
intersession repeatability results, Table 4 summarizes the
differences between sessions and their statistical compari-
son, and Table 5 summarizes the results of the intraclass
correlation analysis.

3.1. Refractive Variables. (ere were no statistically signif-
icant differences (P≥ 0.05) between sessions in both groups
for all the refractive variables.

Concerning spherical equivalent (M), the Eye Refract
was more repeatable in healthy subjects (Sr � 0.27 D)
compared to those with keratoconus (Sr � 0.65 D), while
there was an excellent intersession agreement in both groups
(ICC≥ 0.90).

Similar results were found for cylindrical vectors. (e
Eye Refract was more repeatable in healthy subjects (J0 :
Sr � 0.09 D; J45 : Sr � 0.06 D) compared to those with ker-
atoconus (J0 : Sr � 0.29 D; J45 : Sr � 0.24 D). Also, both J0 and
J45 showed an excellent intersession agreement in both
groups (ICC≥ 0.90).

3.2. Visual Acuity. In the case of BCDVA, there were no
statistically significant differences (P≥ 0.05) between ses-
sions in both groups, and the Eye Refract showed the same
repeatability in both healthy and keratoconus subjects
(Sr � 0.04 logMAR). However, the intersession agreement
was excellent in keratoconus subjects (ICC� 0.953), while it
was decreased in healthy subjects (ICC� 0.748).

3.3. SpentTime inRefraction. About spent time in refraction,
the one-way ANOVA showed statistically significant dif-
ferences (P< 0.05) between the three sessions in both
groups, being the time reduced as the sessions went by. (e
Eye Refract was more repeatable in healthy subjects

Table 1: Demographic characteristics of the participants in the study.

Group Number of participants Age (years) Age range (years) Gender (M/F)
Healthy 33 38.85± 13.21 [18, 65] 14/19
Keratoconus 31 37.29± 11.37 [19, 65] 16/15

Table 2: Inclusion and exclusion criteria of the participants in the study.

Inclusion criteria Exclusion criteria
Healthy Keratoconus Healthy Keratoconus

Age between 18 and 65 years
Presence of any ocular disease or
surgery (apart from keratoconus, in

this group)

Understanding and signing the informed consent Use of systemic or ocular drugs that
could affect the results

— With or without intracorneal ring segments Spherical error higher than± 15.00
D

— Stage I, II, or III, according to Amsler–Krumeich classification Cylindrical error higher than± 8.00
D

Figure 1: Image of the Eye Refract system and the digital screen
used.

Journal of Ophthalmology 3



(Sr � 31 s) compared to those with keratoconus (Sr � 0 : 44 s),
while, on the contrary, the intersession agreement was
higher in keratoconus subjects (ICC� 0.808) than in healthy
ones (ICC� 0.500).

4. Discussion

(e current study is the first to evaluate the repeatability of
the Eye Refract to perform aberrometry-based automated

Table 3: Intersession repeatability of the three sessions in terms of repeatability (Sr) and its 95% confidence interval (r) for spherical
equivalent (M), cylindrical vectors (J0 and J45), binocular corrected visual acuity (BCDVA), and spent time in refraction.

Variable Group
Mean± SD

Repeatability (Sr) 95% confidence interval (r)
Session 1 Session 2 Session 3

M (D) Healthy −1.06± 2.54 −1.06± 2.48 −1.02± 2.50 0.27 0.74
Keratoconus −4.76± 4.82 −4.45± 4.66 −4.42± 4.72 0.65 1.82

J0 (D) Healthy 0.05± 0.38 0.06± 0.39 0.07± 0.35 0.09 0.26
Keratoconus −0.71± 1.49 −0.78± 1.44 −0.79± 1.53 0.29 0.81

J45 (D) Healthy 0.07± 0.25 0.06± 0.21 0.06± 0.24 0.06 0.18
Keratoconus −0.05± 1.24 0.01± 1.29 −0.01± 1.28 0.24 0.67

BCDVA (logMAR) Healthy −0.21± 0.12 −0.22± 0.07 −0.23± 0.08 0.04 0.12
Keratoconus 0.04± 0.21 0.04± 0.20 0.06± 0.22 0.04 0.12

Time (min : s) Healthy 4 : 43± 0 : 47 4 : 01± 0 : 37 4 : 00± 0 : 44 0 : 31 1 : 26
Keratoconus 5 : 31± 1 : 40 5 :12± 1 : 35 5 : 02± 1 : 48 0 : 44 2 : 03

Table 4: Mean difference between sessions (bias) and its standard deviation (SD) for spherical equivalent (M), cylindrical vectors (J0 and
J45), binocular corrected visual acuity (BCDVA), and spent time in refraction.

Variable Group Session 1-session 2 Session 1–session 3 Session 2-session 3 ANOVA (P value)

M (D)
Healthy Bias± SD 0.00± 0.07 −0.04± 0.08 −0.04± 0.05 0.806

P value >0.999 >0.999 >0.999

Keratoconus Bias± SD −0.32± 0.18 −0.35± 0.17 −0.03± 0.13 0.146
P value 0.245 0.166 >0.999

J0 (D)
Healthy Bias± SD −0.01± 0.02 −0.02± 0.02 −0.01± 0.03 0.607

P value >0.999 >0.999 >0.999

Keratoconus Bias± SD 0.07± 0.07 0.08± 0.08 0.01± 0.08 0.511
P value 0.913 0.944 >0.999

J45 (D)
Healthy Bias± SD 0.00± 0.02 0.01± 0.02 0.01± 0.02 0.756

P value >0.999 >0.999 >0.999

Keratoconus Bias± SD −0.06± 0.05 −0.05± 0.07 0.02± 0.06 0.518
P value 0.748 >0.999 >0.999

BCDVA (logMAR)
Healthy Bias± SD 0.01± 0.01 0.02± 0.01 0.00± 0.01 0.425P value >0.999 0.621 >0.999

Keratoconus Bias± SD 0.01± 0.01 −0.02± 0.01 −0.02± 0.01 0.143
P value >0.999 0.707 0.142

Time (min : s)
Healthy Bias± SD 0 : 22± 0.07 0 : 23± 0 : 09 0 : 01± 0 : 05 0.011∗

P value 0.007¥ 0.037¥ >0.999

Keratoconus Bias± SD 0 : 20± 0 : 08 0 : 30± 0 :13 0 :10± 0 :11 0.047∗
P value 0.080 0.081 >0.999

(e statistical comparison was performed between sessions. ∗P< 0.05, one-way ANOVA for related samples. ¥P< 0.05, pairwise comparison with Bonferroni
correction.

Table 5: Intraclass correlation coefficient (ICC) and its 95% confidence interval for spherical equivalent (M), cylindrical vectors (J0 and J45),
binocular corrected visual acuity (BCDVA), and spent time in refraction.

Group
Intraclass correlation coefficient (95% confidence interval)

M J0 J45 BCDVA Time
Healthy 0.989 (0.980, 0.994) 0.935 (0.888, 0.965) 0.929 (0.878, 0.961) 0.748 (0.605, 0.855) 0.500 (0.295, 0.687)
Keratoconus 0.981 (0.966, 0.990) 0.961 (0.931, 0.980) 0.964 (0.936, 0.981) 0.953 (0.917, 0.975) 0.808 (0.686, 0.894)

4 Journal of Ophthalmology



subjective refraction in both healthy and keratoconus sub-
jects. (e intersession repeatability analysis showed no
statistical differences between the three sessions in both
groups for M, J0, J45, and BCDVA, while the values of
repeatability for all the refractive variables were better in
healthy subjects. Conversely, the values of repeatability for
the BCDVA were similar in both groups.

Analyzing the results of spherical equivalent (M), it was
found that the Eye Refract was more repeatable in healthy
subjects compared to those with keratoconus for all three
sessions (see Table 4). Although the r value was 2.41 times
lower in healthy subjects (r� 0.74 D) than in keratoconus
subjects (r� 1.82 D), the values of ICC were excellent and
similar in both groups (see Table 5). (is fact would suggest
that reporting a single statistical variable could not be
enough for repeatability analysis. In agreement with our
results, Raasch et al. [22] found that traditional subjective
refraction was also more repeatable in healthy subjects
(r� 1.00 D) than in those with keratoconus (r� 10.56 D).
(ey reported higher r values than the current study, which
could give the impression that the Eye Refract is more re-
peatable than traditional subjective refraction to assess
spherical equivalent. Supporting this idea, Davis et al. [23]
also obtained higher r values (r� 5.70 D) for the sphere with
traditional subjective refraction in keratoconus subjects.
However, this previous affirmation should be carefully
interpreted because there are differences between these two
studies and the current one that would not make them
comparable, such as sample characteristics, number of
sessions, or number of days between sessions.

Concerning other methods of refraction in keratoconus
subjects, Shetty et al. [24] showed similar values of ICC for
the sphere in both healthy and keratoconus subjects with an
adaptive optics visual simulator. Because they only reported
values of ICC, we would like to emphasize the importance of
analyzing other statistical variables for repeatability analysis.
On the other hand, Piñero et al. [25] measured objective
refraction with an aberrometer in keratoconus subjects.(ey
found similar values of repeatability for the sphere (r� 1.96
D; ICC� 0.983) compared to the Eye Refract in the kera-
toconus group (see Table 3). In healthy subjects, several
studies measured objective refraction with different aberr-
ometers, obtaining r values between 0.28 D and 0.59 D for
the spherical equivalent [16, 26–30]. (ese values were
slightly better than the ones obtained with the Eye Refract in
the healthy group (see Table 3).

(e intersession repeatability analysis of astigmatism (J0
and J45) showed the same results as the analysis of spherical
equivalent. (e Eye Refract was more repeatable in healthy
subjects compared to those with keratoconus for all three
sessions (see Table 4), being the r values 3.12 and 3.72 times
lower in healthy subjects for both J0 and J45, respectively.
(e values of ICC were also excellent and similar in both
groups (see Table 5). Again, Raasch et al. [22] found that
traditional subjective refraction was more repeatable for
astigmatism assessment in healthy subjects (J0: r� 0.45 D;
J45: r� 0.31 D) compared to those with keratoconus (J0:
r� 3.86 D; J45: r� 2.96 D), reaching worse repeatability than
the Eye Refract in both groups (see Table 3). Additionally,

Davis et al. [23] also obtained higher r values for the cylinder
(r� 2.72 D) with traditional subjective refraction in kera-
toconus subjects.

With an adaptive optics visual simulator, Shetty et al.
[24] showed similar values of ICC for the cylinder between
healthy and keratoconus subjects, again with the limitation
that they did not analyze other statistical variables for re-
peatability analysis. With an aberrometer, Piñero et al. [25]
found better repeatability in keratoconus subjects for J0
(r� 0.45 D) compared to the Eye Refract in the keratoconus
group, but worse for J45 (r� 1.55 D) (see Table 3). In healthy
subjects, several studies measured astigmatism with different
aberrometers, obtaining similar or slightly better values of
repeatability compared to the current study [16, 26–30].

Although no studies evaluating repeatability of auto-
mated subjective refraction in keratoconus subjects were
found in the scientific literature, some authors evaluated it in
healthy subjects [10–13, 15]. With the first instrument to
perform automated subjective refraction, the BV-1000
(Topcon; Tokyo, Japan), Dave and Fukuma [10] found better
repeatability in all the refractive variables (M, J0, and J45)
than the Eye Refract in the healthy group. Conversely,
Sheedy et al. [11] showed similar repeatability with the same
instrument compared to the Eye Refract for M and J0 de-
termination, but slightly worse for J45. On the other hand,
Perches et al. [12] evaluated a virtual system of automated
subjective refraction in only three participants, but by fifty
external evaluators per participants. (ey found better re-
peatability in the two participants with low astigmatism
compared to the one with high astigmatism. Pujol et al. [13]
also measured repeatability with a 3D virtual reality in-
strument of automated subjective refraction, showing
slightly better results in terms of Sr and ICC values for M
than the Eye Refract in the healthy group. Finally, Otero et al.
[15] used an automated system composed of an open-field
autorefractometer and a phoropter with which they obtained
better repeatability than the Eye Refract for M and J0 de-
termination, but worse for J45.

In terms of BCDVA, the intersession repeatability
analysis showed the same results for both healthy and
keratoconus subjects. (ere were no statistical differences
between sessions, and the r values were identical (see
Tables 3–4). However, the ICC was lower in healthy subjects
(ICC� 0.748) compared to those with keratoconus
(ICC� 0.953). To our knowledge, only a pair of studies
evaluated the intersession repeatability of traditional sub-
jective refraction for high-contrast BCDVA in keratoconus
subjects [23, 31]. (ey found r values to be approximately
twice compared to the keratoconus group of the current
study in addition to a worse ICC (0.769).

One of the advantages of automated subjective refract
would be that spent time in refraction is reduced compared
to traditional subjective refraction [14, 15]. (is is possible
due to both objective and subjective refractions that are
incorporated into a single instrument. (e most remarkable
aspect of repeatability analysis was that the spent time with
the Eye Refract reduced in both groups as the sessions went
by (see Table 3), which could be associated with a learning
process by the participants.

Journal of Ophthalmology 5



(e main limitation of the current study was that in-
tersession repeatability of other methods of refraction, in
addition to that of the Eye Refract, was not assessed.
(erefore, the advantages of the Eye Refract compared to
another of these mentioned methods should be carefully
treated due to methodological differences between studies.

5. Conclusions

(e Eye Refract offered better repeatability to assess re-
fractive errors in healthy subjects compared to those with
keratoconus. Despite measurements being also consistent in
keratoconus subjects, they should be treated with caution in
clinical practice.

Data Availability

(e data used to support the findings of this study are
available from the corresponding author upon request.

Conflicts of Interest

(e authors declare that they have no conflicts of interest.

Acknowledgments

(e authors would like to thank Luneau Technology for
providing the Eye Refract during the conduct of the study.
Gonzalo Carracedo received a personal grant from Luneau
Technology (Chartres, France) for the performance of the
study.

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