Why do we still not know whether refractive error causes headaches? Towards a framework for evidence based practice Gael E. Gordon 1 , Edward P. Chronicle 2 and Paul Rolan 3 1 Studiengang Augenoptik, Fachochschule Aalen, Gartenstrasse 135, 73430 Aalen, Germany, 2 Department of Psychology, Unit for Mental Health and Neural Systems Research, Fylde College, Lancaster University, Lancaster LA1 4YF, UK and 3 Department of Neurology, Head Pain Clinic, Manchester Royal In®rmary, Manchester M13 9WL, UK Summary In this paper, we systematically review the available experimental and clinical evidence concerning the causation of headache by refractive error. Despite the apparent belief of both medical and optometric professionals that provision of an appropriate correction may alleviate various types of headache, there is little if any robust evidence in support of this position. We identify four serious methodological and theoretical dif®culties with studies to date, which currently render it impossible to assess the relationship between refractive error and headache. The provision by the Inter- national Headache Society of the diagnostic category ªheadache associated with refractive errorº is called into question. Five research questions are posited in the form of a framework for the development of evidence-based practice in optometry and the treatment of headache. q 2000 The College of Optometrists. Published by Elsevier Science Ltd. All rights reserved. Introduction It is commonly believed that refractive errors and binocular vision anomalies may result in headache and eyestrain in a vulnerable individual. The present paper reviews the evidence for a relationship between headache and refractive error. Most ophthalmic practitioners will testify that head- ache is a common patient complaint. Whittington (1958) reported that of more than 1400 consecutive patients attend- ing for refraction, 45% complained of headache. There is some evidence that headache is also an important presenting symptom in children (Elkins, 1991 cited by Barnard and Edgar, 1996). Furthermore, the International Headache Society (IHS), the medical body currently responsible for the diagnostic classi®cation of headache disorders, provides for the category 11.3.2 [Headache Associated With] Refrac- tive Errors (IHS, 1999). Diagnostic criteria are as follows: ªA. Uncorrected refractive errors, e.g. hypermetropia, astigmatism, presbyopia, wearing of incorrect glasses. B. Mild headaches in the frontal region and in the eyes them- selves. C. Pain absent on awakening, and aggravated by prolonged visual tasks at the distance or angle where vision is impaired.º Interest in this subject has been bolstered over the last 10 years by concern over the effects of extended visual display terminal use (VDUs and eyestrain have been extensively reviewed (e.g. see Thomson, 1998) and will be considered only brie¯y here). It is therefore surprising that systematic experimental investigation of the role of refractive error in headache has seldom been conducted; neither does the IHS cite any evidence in support of its classi®cation. The subject has been dominated instead by clinical anecdote throughout the 20th century (Gould, 1904; Snell, 1904; Baker, 1907; Harris, 1934; Chamlin, 1962; Behrens, 1978; Hedges, 1979; Sandy, 1983; Tomsak, 1991; Daroff, 1995). The issue has been clouded moreover, by the failure of researchers adequately to classify headache in studies to date: typically, heterogeneous groups have been examined, with presumably different headache pathogenesis. This paper aims to review critically the available 45 Ophthal. Physiol. Opt. Vol. 21, No. 1, pp. 45±50, 2001 q 2000 The College of Optometrists. Published by Elsevier Science Ltd All rights reserved. Printed in Great Britain 0275-5408/00/$20.00 www.elsevier.com/locate/ophopt PII: S0275-5408(00)00033-8 Received: 27 July 1999 Revised form: 20 April 2000 Accepted: 23 April 2000 Correspondence and reprint requests to: Gael E. Gordon.