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Editorial Corneal Disorders Is Keratoconus Really Rare? Nikki Hafezi 1,2 and Farhad Hafezi 1,3 1. ELZA Institute, Dietikon/Zurich, Switzerland; 2. Light for Sight Foundation, Zurich, Switzerland; 3. USC Roski Eye Institute, University of Southern California, Los Angeles, CA, US T he most used prevalence rate of keratoconus is 1:2,000, which defines the disease as rare. More recent studies suggest that the prevalence is significantly higher than 1:2,000. This increase in prevalence may be explained by the introduction of modern and highly sensitive corneal imaging technologies and a better understanding of geographical variations in the prevalence of keratoconus. The K-MAP study (NCT03115710) will determine the global prevalence of keratoconus in the young population and thus help support the introduction of screening initiatives for this not-so-rare disease. Keywords Keratoconus, cross-linking, prevalence, children, adolescents Disclosure: Nikki Hafezi and Farhad Hafezi have nothing to declare in relation to this article. This article is a short opinion piece and has not been submitted to external peer reviewers. No funding was received in the publication of this article. Authorship: All named authors meet the International Committee of Medical Journal Editors (ICMJE) criteria for authorship of this manuscript, take responsibility for the integrity of the work as a whole, and have given final approval to the version to be published. Open Access: This article is published under the Creative Commons Attribution Noncommercial License, which permits any noncommercial use, distribution, adaptation, and reproduction provided the original author(s) and source are given appropriate credit. Received: July 21, 2017 Published Online: October 20, 2017 Citation: US Ophthalmic Review, 2017;10(2):91–2 Corresponding Author: Nikki Hafezi, ELZA Institute, Webereistrasse 2, 8953 Dietikon, Switzerland. E: Despite the successful translation of corneal cross-linking (CXL) into clinical practice for the therapy of progressive ectasia, keratoconus globally still remains a major reason for severe visual impairment in the young population. Keratoconus is characterized by a biomechanical weakening effect on the corneal stroma. This disease is typically most aggressive in the first three decades of life, and then slows down to an arrest in the fourth to fifth decade. The prevalence of keratoconus has first been investigated in the 1980s, when Kennedy and colleagues detected keratoconus based on irregular retinoscopic reflexes and irregular mires detected with keratometery. 1 Their study was conducted in the US, and the prevalence reported was 1 in 2,000 patients, which, by definition, is a rare disease. Despite the study being 30 years old, it remains the most cited prevalence rate of keratoconus. However, a number of more recent publications indicate that the occurrence of this disease might be considerably more frequent than previously estimated. This might be due to the following reasons. Changes in corneal imaging techniques Corneal imaging techniques have evolved since the mid-1980s. In 1985, Klyce and colleagues introduced the concept of modern corneal topography with computer-assisted analysis of the reflection image from Placido photokeratoscope images. 2 About 20 years later, Scheimpflug imaging technology allowed for a more detailed analysis of both the corneal anterior and posterior surface, coining the term “corneal tomography.” 3,4 Measurement of corneal biomechanics in vivo Technology has advanced to help analyze corneal biomechanics and detect early forms of keratoconus with a greater sensitivity. The Ocular Response Analyzer (ORA), originally developed by David Luce in the mid 2000s, was the first of its kind to measure the corneal deformation based on an air puff. 5 A few years later, high-speed dynamic Scheimpflug imaging allowed for a more detailed analysis of the changes induced by an air puff. 6 Now, new indices are being developed to allow for a better characterization of keratoconus at an early stage. 7 More recently, Brillouin microscopy, a means to measure corneal biomechanics in a depth-dependent manner is promising and is in its first clinical stages of development. 8 Major geographical variations The reported prevalence and incidence rates for keratoconus are varied. Geographic, environmental and ethnic factors may be influencing the differing rates; furthermore, interrelations between these factors are also yet to be determined. TOU CH MED ICA L MEDIA 91