Obesity and Obstructive Sleep Apnea in Patients With
Keratoconus in a Turkish Population
Baran Gencer, MD,* Engin Bilge Ozgurhan, MD,† Selcuk Kara, MD,* Hasan Ali Tufan, MD,*
Sedat Arikan, MD,* Ercument Bozkurt, MD,† and Ahmet Demirok, MD†‡
Purpose: The aim of this study was to compare the frequency of
occurrence of obesity and high risk of developing obstructive sleep
apnea (OSA) in a keratoconus population with that of a control
Methods: This prospective, case-controlled multicenter study was
performed on patients with keratoconus and age- and gender-
matched control subjects. One hundred forty-six patients were
included in each group, and the Berlin Questionnaire was used for
classifying patients as having a high risk or low risk of developing
OSA. The patients’ demographic and clinical characteristics were
compared with the Mann–Whitney U test for continuous variables
and with the x2test for categorical variables.
Results: The keratoconus (85 male/61 female) and control (79
male/67 female) groups’ median ages were 25 (8–65) and 24 (9–60)
years, respectively. Of the 146 patients in each group, 11 (7.5%)
patients were determined to be at a high risk of developing OSA in
the keratoconus group, and 8 (5.5%) patients were determined to be
at a high risk of developing OSA in the control group. There was no
significant difference between the groups (P = 0.477). The kerato-
conus and control groups’ median body mass index values were
found to be within normal ranges of 23.2 and 23.4, respectively.
Conclusions: In this study, the mean body mass index value of the
keratoconus group was determined to be within normal limits. In
a Turkish population, the ratio of a high risk of developing OSA was
not found to be significantly different between the keratoconus and
Key Words: keratoconus, obstructive sleep apnea, obesity
Keratoconus has been linked to Down syndrome,2Leber con-
eratoconus is a noninflammatory ectatic disease character-
genital amaurosis,3Ehlers–Danlos syndrome,4mitral valve pro-
lapse,5and floppy eyelid syndrome.6–8
Obstructive sleep apnea (OSA) is a clinical condition
characterized by repeated episodes of apnea and hypopnea,
which may cause daytime sleepiness.9The important clinical
symptoms of the disease have a wide spectrum, including
exceptional daytime sleepiness,10cognitive dysfunction,11car-
diovascular diseases (hypertension, stroke, myocardial infarc-
tion, and heart failure),12,13and metabolic dysfunction.14,15The
most important demographic risk factors for this disease are
obesity, age, and male gender.16,17OSA has been linked to
some eye diseases, such as floppy eyelid syndrome,18,19glau-
coma,20nonarteritic anterior ischemic optic neuropathy,21and
Firstly, Smolin23reported the relationship between OSA
and keratoconus. Since the realization that both OSA and ker-
atoconus are linked to the floppy eyelid syndrome, researchers
have recently attempted to investigate the prevalence of OSA in
patients with keratoconus. The prevalence of OSA in patients
with keratoconus has been found to be in the range of 18% to
24% in the previous 3 studies, and these results were higher
than the prevalence of OSA in the general population.24–26
However, all these studies were conducted in the United States,
and the body mass index (BMI) of patients with keratoconus
was found to be between 29.9 and 32.42 kg/m2.24–26In the
United States, obesity is a growing public health problem,
and about a third of adults are reported to be obese.27The
relationship between keratoconus and obesity is unclear.28,29
The aim of this prospective study was to investigate the
relationship between obesity and OSA in patients with
keratoconus by comparing a group of patients with kerato-
conus with a control group in the Turkish population.
MATERIALS AND METHODS
This prospective study was completed in compliance
with the ethical standards of the 1964 Helsinki Declaration,
with the protocol was approved by the Beyoglu Eye Education
and Research Hospital local ethics committee. Signed informed
consents were obtained from the patients who were included in
this study between May 2012 and April 2013.
The keratoconus group comprised patients who were
followed up at the Department of Ophthalmology, Canakkale
Onsekiz Mart University, and Beyoglu Eye Education and
Research Hospital. The diagnosis of keratoconus was made
based on the following criteria (at least 1 sign): Munson sign,
Rizzuti sign, stromal thinning, conical protrusion, Fleischer
Received for publication June 17, 2013; revision received July 22, 2013;
accepted October 2, 2013. Published online ahead of print December 6,
From the *Department of Ophthalmology, School of Medicine, Canakkale
Onsekiz Mart University, Canakkale, Turkey; †Beyoglu Eye Research
and Training Hospital, Istanbul, Turkey; and ‡Department of Ophthalmol-
ogy, School of Medicine, Istanbul Medeniyet University, Istanbul, Turkey.
The authors have no funding or conflicts of interest to disclose.
Reprints: Baran Gencer, Department of Ophthalmology, School of Medicine,
Canakkale Onsekiz Mart University, Canakkale, Turkey (e-mail:
Copyright © 2013 by Lippincott Williams & Wilkins
Cornea ? Volume 33, Number 2, February 2014 www.corneajrnl.com|137
ring, Vogt striae, and topographic signs consistent with
keratoconus. The diagnosis of keratoconus was confirmed
by measurements using a Scheimpflug camera combined with
Placido corneal topography (CSO; Sirius, Firenze, Italy).
Keratoconus was graded by using a modified keratoconus
severity score (Table 1).30Patients with a history of ocular
surgery, suspected keratoconus, form fruste keratoconus, and
other active ocular diseases were excluded from the study.
The control group was matched for age and sex with the
keratoconus group. The patients were randomized from
patients in the Department of Ophthalmology, Canakkale
Onsekiz Mart University, and also from among volunteer
hospital personnel by an examiner (B.G.) blinded to the
keratoconus group. The patients included in the study met the
criteria for grade 0 (normal) in Table 1. Exclusion criteria
were astigmatism .2 diopters, slit-lamp findings of kerato-
conus, and a history of ocular surgery.
The patients were questioned primarily about their OSA
history, and the Berlin Questionnaire (BQ) was used to
evaluate the risk of developing OSA. Using the BQ, which
has 3 parts, patients were reliably classified as being at a high
or low risk of developing OSA. The criteria were snoring
behavior, daytime sleepiness, and high blood pressure or
obesity (BMI $30 kg/m2). If 2 of these 3 conditions were
present, patients were classified as being at a high risk of
Statistical analysis was completed using the Statistical
Package for Social Sciences (SPSS) version 15.0 for Windows
(SPSS, Chicago, IL). Variables with a normal distribution were
investigated with the Kolmogorov–Smirnov test. Demographic
and clinical characteristics of keratoconus and control groups
were compared using the Mann–Whitney U test for continuous
variables and the x2test for categorical variables. Significance
was accepted at P , 0.05.
The keratoconus and control groups comprised 146
patients in each group. The demographic and clinical
characteristics of both groups are shown in Table 2. The
control group was matched for age (P = 0.703) and gender
(P = 0.479) with the keratoconus group (Table 2). When the
patients with keratoconus were graded for mild, moderate,
and severe groups, their numbers were determined as 126,
10, and 10, respectively.
In both keratoconus and control groups, there was no
patient with a history of OSA. In the keratoconus group, the
median value of BMI (P = 0.617), percentage of obese pa-
tients (P = 0.144), and percentage of patients at a high risk of
developing OSA (P = 0.477) as identified by the BQ were not
significantly different when compared with those of the con-
trol group. When the patients of the keratoconus and control
groups were classified as being at a high or low risk of devel-
oping OSA, there was no significant difference for gender
between high- and low-risk groups; in the high-risk group,
age and BMI were found to be significantly higher compared
with that of the low-risk group (Table 3).
This study evaluated the status of obesity and the risk of
developing OSA in patients with keratoconus as determined
by the BQ by comparing them with age- and gender-matched
controls. When compared with the control group, no signif-
icant differences were found in the percentages of patients
found to be obese or at a high risk of developing OSA in the
keratoconus group. Patients at a high risk of developing OSA
had a statistically significant higher age and BMI in both the
keratoconus and control groups.
Gupta et al24found the prevalence of OSA to be 18%
and high-risk cases identified by the BQ to be 47% in 101
patients with keratoconus. This study did not use a control
group, and the values were significantly higher than the OSA-
prevalence values in the previous studies. In this study, we
interviewed patients with keratoconus by telephone, and the
average BMI was found to be 31.2 kg/m2. In another study
TABLE 1. Keratoconus Severity Score Ranking Scheme
Unaffected-NormalUnaffected-Atypical KC Suspect Affected-Mild Affected-ModerateAffected-Severe
Average corneal power
Higher-order RMS error
IP, ASBT, AIBT
ISP, SSP, CSP
AIBT, asymmetric inferior bow tie; ASBT, asymmetric superior bow tie; CSP, central steep pattern; IP, irregular pattern; ISP, inferior steep pattern; KC, keratoconus; RMS, root
mean square; SSP, superior steep pattern.
TABLE 2. Demographic and Clinical Characteristics of the
Keratoconus and Control Groups
Keratoconus (n = 146)Control (n = 146)
High risk of OSA
Values are given as median (range) for continuous variables and number
(percentage) for categorical variables.
*P values are from the x2test for categorical variables and from the Mann–Whitney
U test for continuous variables.
Gencer et al
Cornea ? Volume 33, Number 2, February 2014
? 2013 Lippincott Williams & Wilkins
that consisted of 92 patients in each of the keratoconus and
control groups, Saidel et al25found that the OSA prevalence
was 19.6% and 6.5%, respectively. In this study, the high-risk
groups of OSA determined by BQ were found to be 53.3%
and 27.2%, respectively. However, in this study, the patients
had an average BMI in the keratoconus and control groups of
29.9 and 27.2 kg/m2, respectively. The BMI values, espe-
cially of the keratoconus group, are borderline obese. The
latest study on this topic, by Pihlblad and Schaefer,26found
that the OSA prevalence in 50 patients with keratoconus was
24%, and the obesity rate was 52%. In all these studies, the
average BMI of the patients was found to be at or above the
obesity limit in the keratoconus groups. However, in the pre-
vious studies, there was no obvious relationship between ker-
atoconus and obesity. Kristinsson et al28have found the
average BMI of patients with keratoconus with a history of
keratoplasty surgery to be significantly higher than that of the
control group in the United States. In contrast to this study,
Jonas et al29identified a significant relationship between
a low BMI and keratoconus in the most comprehensive study
of 4667 patients with keratoconus conducted in India. When
considering these studies, it seems that the previous 3 studies
conducted for OSA prevalence in patients with keratoconus
may probably represent the US population. Because obesity is
the most important risk factor for OSA, it is evident that OSA
prevalence will be high in groups with a high BMI.
In our study, median BMI values were found to be
23.2 kg/m2in the keratoconus group and 23.4 kg/m2in the
control group; both of them were within normal ranges. The
percentage of obese patients was 8.2% in the keratoconus
group and 4.1% in the control group. The percentage of pa-
tients at a high risk of developing OSA determined by the BQ
was 7.5% and 5.5% for the keratoconus and control groups,
respectively. These values are similar to the range of OSA
prevalence of 4.9% to 6.4% found in the previous studies.31,32
In both the keratoconus and control groups, the median BMI
(P = 0.001, 0.002) and age (P = 0.005, 0.031) values of high-
risk groups for OSA were significantly higher than those in the
low-risk groups. These data are compatible with those in the
literature; therefore, it increases the reliability of this study.33
Contrary to the other studies, in this study, the rate of patients
with a high risk of developing OSA as determined by the BQ
in the keratoconus group was not found to be higher than that
in the control group. We thought that this result may be related
to the normal BMI values that were found in both keratoconus
and control groups. Nevertheless, we should also mention that
because keratoconus is a heterogeneous disease, there may be
differences among countries for the high risk of OSA in
A limitation of this study is the evaluation of OSA risk
only with BQ rather than confirmation with polysomnogra-
phy. Although the BQ for OSA risk evaluation is a widely
used and reliable test, patients usually do not respond to the
questions about their snoring behaviors. This obstacle
increases the error margin for this test. When compared with
the other studies, the questionnaire was completed during
face-to-face interviews with patients in this study, which
reduces the error margin for the test.
In the light of these results, it is necessary to carry out
additional studies with a wider series of patients and in
populations with different socioeconomic and racial charac-
teristics to evaluate the OSA prevalence in patients with
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