Myopia - genes or environment? The refractive properties of the eye are determined by a large number of variables, a few of which are the length of the eye, the radius of curvature of the cornea, the thickness and position of the lens and the refractive indices of the various media. Most people have either no refractive error or only very slight refractive anomalies that do not progress beyond a degree consistent with the range of normal development. These refractive errors are associated with good vision and require no treatment apart from their optical correction. In myopia, when the eye is at rest, parallel rays of light come to a focus in front of the retina, producing a blurred image that requires correction with concave lenses. In most myopes their condition first becomes evident between the age of 5 and puberty. The myopia may progress during the growing period until adolescence is passed and the eye stabilizes. In a few myopes, however, there is a rapid progression of the refractive error, associated with degenerative changes in the retina and vitreous, which produces visual im-

pairment and even blindness from the many complications. In many Western societies degenerative myopia is, in fact, an important cause of blindness, along with cataracts, glaucoma and diabetic retinopathy. Several studies have suggested that myopia is genetically determined and is probably autosomally dominant in its transmission.' There has been no general agreement on the mode of transmission and some observers believe that it is most commonly a recessive characteristic. Although heredity has held the stage as the main epidemiologic factor in myopia, a number of isolated pieces of evidence suggest that genetic transmission is not wholly responsible for the error and that environmental factors are important.2 In 1970 and 1971, with the backing of the Department of National Health and Welfare, eye surveys of total Arctic communities were undertaken by the universities of Alberta and British Columbia and McGill University. The results of the surveys were presented in a symposium organized by the Cana-

WORKSHOP ON WRITING FOR MEDICAL JOURNALS Tuesday, June 24, 1975 Palliser Hotel, Calgary 9 a.m. to 5 p.m. * Do you want to make your scientific writing more effective, more interesting, more acceptable? * Are you interested in the principles of effectively organizing medical papers and reports? * Do you want to learn how to prepare papers to convince editors, reviewers and readers? If so, attend a 1-day workshop to be held during the CMA annual meeting. Workshop will include discussion of preworkshop assignments and various aspects of medical writing. Faculty: David A. E. Shephard, M.B., F.R.C.P.(C) Associate scientific editor, CMAJ David Woods Consultant, Medical Communications Services

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Registration limited to 25 participants. Deadline for registration: May 15, 1975. Fee: $40. For further details write to: Dr. David A. E. Shephard, Associate scientific editor, CANADIAN MEDICAL ASSOCIATION. Box 8650, Ottawa, Ont. KIG OGS.

552 CMA JOURNAL/MARCH 8, 1975/VOL. 112

dian Ophthalmological Society and published in the April 1973 issue of the Canadian Journal of Ophthalmology. The most dramatic finding was that myopia was four to eight times more frequent in those 15 to 30 years old than in their elders.3. A similar finding had previously been noted in studies of Inuit populations in Alaska.6 A number of possible explanations for these findings were suggested but it was clear that environmental factors would have to be seriously examined and studied. In this issue of the Journal (page 575), Morgan, Speakman and Grimshaw report on a followup study of two isolated Arctic communities, Gjoa Haven and Spence Bay, designed to test the genetic hypothesis of the inheritance of myopia and to study the effects of some environmental factors. The study failed to support the influence of heredity on the production of myopia in the Inuit but suggested that schooling could be one of the environmental factors implicated in the epidemic. Such a possibility is supported by some experimental work on primates that were made myopic by an encroachment on their visual space.7 The prevalence of myopia in young Inuits and the possibility of important environmental etiologic factors, either alone or in conjunction with some underlying genetic mechanisms, should stimulate research into the factors involved. Environmental factors will have to be confirmed in other populations. An understanding of these factors has important practical implications that could lead to the prevention of myopia and a consequent reduction in visual impairment and even blindness from this cause. STEPHEN M. DRANCE, MD

Department of ophthalmology The University of British Columbia Vancouver, BC

References 1. WARDENBURO N: Hornhautastigmatismus und Monatsbl AugenHornhautbrechung. Kim heilkd 85: 31, 1930 2. GOLDSCHMIDT E: (On the etiology of myopia. An epidemiological study.) Acta Ophthalmoi (Kbh) 98 (suppl): 31, 1968 3. MORGAN RW MUNRO M: Refractive problems in northern 'natives. Can J Ophthalmol 8: 226, 1973 4. BoNIuK V: Refractive problems in native peoples (the Sioux Lookout Project). Ibid. p 229 5. CAss E: A decade of northern ophthalmology. Ibid, p 210 6. YOUNG FA, LEARY GA, BALDWiN WR, et al: The transmission of refractive errors within Eskimo families. Am I Optom 46: 676, 1969 7. YOuNG FA: The effect of restricted visual space on the refractive error of the young monkey eye. Invest Ophthaimoi 2: 571, 1963

Editorial: Myopia - genes or environment?

Myopia - genes or environment? The refractive properties of the eye are determined by a large number of variables, a few of which are the length of th...
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