CLINICAL SCIENCE Prevalence of Sleep Apnea in Patients With Keratoconus Preeya K. Gupta, MD,* Sandra S. Stinnett, DrPH,* and Alan N. Carlson, MD* Purpose: To determine the prevalence of obstructive sleep apnea (OSA) in patients with keratoconus and evaluate the risk of developing OSA in this patient population. Methods: Three hundred sixty-two patients diagnosed with keratoconus by a single physician at the Duke Eye Center over a 14-year period were identified. A power calculation was done a priori, and based on this, the first 101 patients were enrolled. All patients were administered a standardized questionnaire regarding medical and ocular health. Those without the history of OSA were administered the Berlin questionnaire to determine their risk for developing OSA. Statistical analysis was performed to determine the prevalence of OSA and to compare it with previously reported prevalence data in the general population. Results: The prevalence of previously diagnosed OSA was 18% (18 of 101); all reported having a formal sleep study in the past. Of the remaining patients (n = 83), 47% (39 of 83) were determined to be at high risk for the development of OSA determined by the Berlin questionnaire score. Comorbid health conditions included hyperten- sion (37%), acid reflux (30%), diabetes mellitus (20%), and seasonal allergies (66%). A history of penetrating keratoplasty was found in 48%. The average body mass index of the study population was 31.2 (median, 28.4). Conclusions: Keratoconus patients have a higher prevalence of OSA compared with that accepted for the general population. A striking number of our patients without previous diagnosis of OSA seem to be at high risk for developing OSA, supporting our recommendation for a greater awareness among clinicians who might otherwise overlook this systemic condition and its conse- quences. Key Words: keratoconus, sleep apnea, epidemiology (Cornea 2012;31:595–599) K eratoconus is a noninflammatory ectatic disorder of the cornea characterized by progressive conical steepening with thinning. 1 It tends to affect younger individuals and can be visually disabling. The reported prevalence of keratoconus in the literature is 54.5 per 100,000. 1,2 Keratoco- nus has been associated with eye rubbing, 3,4 and a variety of systemic conditions, including Ehlers–Danlos syndrome, Marfan syndrome, atopic disease, 5 Down syndrome, 6 and floppy eyelid syndrome. Obstructive sleep apnea (OSA) is a clinical syndrome characterized by recurrent episodes of apnea and hypopnea during sleep associated with daytime sleepiness. It has been associated with multiple comorbid conditions, such as hypertension, 7 cardiac arrhythmias, 8 cardiovascular disease, 9 gastroesophageal reflux, and obesity. 10,11 OSA has been found to be an independent risk factor for stroke and death 12 and has been associated with an increased mortality rate. 13 The prevalence of OSA in adult men in the Western popula- tion is approximately 1% to 5% in the literature, 14,15 although 4% is a commonly accepted number. The prevalence of OSA does vary by age, with peak prevalence of nearly 5% between 45 and 65 years. 16 The prevalence of OSA in women has been reported to be 2%, slightly less than men. 17 Historically, keratoconus has been a relatively common indication for performing corneal transplantation in a young patient. Yet it has been our observation that these postker- atoplasty patients, now in their 50s and 60s and elderly keratoconus patients in general, are somewhat sparse in their anticipated representation among our aging clinic population. Although this could certainly represent selection bias in a university setting, speculation also leads us to further investigate associated or systemic conditions that could possibly increase mortality in keratoconus patients. Floppy eyelid syndrome has been associated with both keratoconus and OSA 18 ; however, there have been no prior studies to specifically examine the association between keratoconus and OSA. The purpose of our study was to determine whether the prevalence of OSA in patients with keratoconus is higher than that reported in the general population and to determine whether patients with keratoconus are at high risk of devel- oping OSA. MATERIALS AND METHODS The study was approved by the Institutional Review Board at the Duke University Medical Center. The codes of International Classification of Diseases, Ninth Revision for keratoconus (371.60, 371.61) were used to search for patients seen at the Duke Eye Center from January 1, 1995, to July 1, 2009, seen by a single physician (A.N.C.). A power calcula- tion was performed before the initiation of the study deter- mining that a minimum sample size of 97 patients would be required to obtain a statistical power of 90% with an a value of 0.05 to assess the difference in the prevalence of sleep Received for publication July 7, 2010; revision received June 5, 2011; accepted June 17, 2011. From the *Department of Ophthalmology, Duke Eye Center, Durham, NC. Presented at the American Society of Cataract and Refractive Surgery Annual Meeting, Boston, MA, April 10, 2010. The authors state that they have no proprietary interest in the products named in this article. Reprints: Alan N. Carlson, Department of Ophthalmology, Duke Eye Center, 2351 Erwin Road, Durham, NC 27710 (e-mail: carls009@mc.duke.edu). Copyright © 2012 by Lippincott Williams & Wilkins Cornea  Volume 31, Number 6, June 2012 www.corneajrnl.com | 595