An ethnic comparison of anterior segment characteristics: A preliminary report

Abstract

Introduction With the introduction of more sophisticated keratometers it has been possible to construct model corneas upon which off the peg type contact lenses may be designed. These are typically aspherical, gas permeable and perhaps ultimately disposable, but essentially contoured to the average cornea. Traditionally however one prescribed individually designed, PMMA lenses which may be retrospectively modified as required and indeed clinical experience frequently suggests variations from the norm can and do occur. Further we practice in a multi-racial society in an era of international travel which must prompt one to question if a lens design on say a caucasian model cornea is equally compatible to a cornea of another patient from a different racial group? The purpose of this paper is to overview some differences in the corneal topography of various ethnic groups in addition to presenting preliminary results of a larger on-going study. Racial Classifications Racial classification is complex, enigmatic and often contradictory. Differences between people come from many sources but are broadly divided into those that are hereditary or genetic and those due to environment. Furthermore, these two factors interact with each other in that the manifestation of the genetic factor depends on the environment. Both J. Z. Young (1971) and C. S. Coon (1965) write of three major poles of differences among the world's people: 1) The Negroids are the principal inhabitants of Africa and generally are dark skinned and spiral haired. Facial features show common everted lips, a broad nose and dark irides. 2) The Caucasoids are the major inhabitants of Europe and Northern America. In general they have the fairest skin and the greatest frequencies of blond hair and light eyes and are characterised by a thin nose and lips. 3) The Mongoloids mainly live in Asia. The principal morphological traits of the mongoloids include coarse, straight black hair, little beard and body hair, yellowish skin, flattish faces with prominent cheek bones. Their noses are either low bridged or aquiline. Their eyes are generally brown with slanted eyelids. Epicanthic eyefold is of higher percentage than the other racial populations. A fourth, smaller population grouping of genes may be called Australoid, characteristic not only of Australian aboriginies but of other people in parts of the East Indies. Their genetic build up shows a dark skin but other characteristics of body form and of hair resemble those produced by Caucasian genes. Structural or morphological variations may of course be considered in terms of regional groupings of genes coupled with presumed environmental interaction. In fact, the distinction of genes usually changes gradually with distance. Therefore, in other words, t he components of men's biological variability change gradually with geographical distance, as for instance, the situation of skin colours, head shape and blood groups. This graduation in distribution makes it impossible to divide men into sharp distinct races and in describing sub-races one may have to rely on a common cetttral tendency from which exceptions can and do occur (Coon, 1965).