The Relationship between Peripheral Refraction, Optical Correction and Myopia Progression

Abstract

It is clear from many sources that the prevalence of myopia is increasing at an alarming rate. Although the pathogenic mechanisms behind the development of myopia remain unclear, various factors have been associated with myopic progression, including genetics, accommodative spasm, prolonged near work, race, gender, educational level, and the amount of time spent outdoors in sunlight. Because of the personal and socio-economic burdens associated with this refractive condition, the key factors in myopia progression continue to be keenly sought. Recent human and animal research suggests that the extent of myopia progression may be dependent on the extent of relative peripheral hyperopia, which in turn is dependent on the type of optical correction (glasses versus contact lenses) worn by an individual. This theory has been termed the hyperopic defocus theory, and the principal goal of this thesis was to assess this current (and popular) theory of myopia development. The methodology employed was a combination of retrospective data analyses and experimental measures of central and peripheral refractive status. Participants selected for inclusion in the study were all myopic, aged 6-24 years, and wore either contact lenses or spectacles. From theoretical arguments and experimental evidence, three hypotheses were made. First, that contact lens wearers will show less myopic progression than spectacle lens wearers. Second, that higher degrees of foveal myopia (myopic progression) arise in eyes with greater amounts of relative peripheral hyperopia. And third, that the dependence of the degree of foveal myopia on relative peripheral refraction is influenced by the type of optical correction worn (contact lenses versus spectacle lenses). In assessing the degree of myopic progression from early childhood through to late adolescence, taking into account the influence of possible covariates (i.e. initial age and initial degree of myopia), the results indicated: (a) optical correction does not have a significant influence on myopic progression; (b) there exists a significant negative correlation between foveal myopic refraction and the degree of relative peripheral hyperopia; and (c) the degree of foveal myopia on relative peripheral refraction is not influenced by the type of optical correction worn. From these results, the first and third hypotheses cannot be supported. These non-confirmatory results of the hyperopic defocus theory, however, are balanced by the supportive finding that higher degrees of foveal myopia arise in eyes with greater amounts of relative peripheral hyperopia (i.e., Hypothesis 2). The latter has important implications for the profession of optometry because, if the theory has genuine merit, it would enable ophthalmic practitioners to not only correct myopia but also minimise the continued development of myopia in children and young adults through various treatment options, including peripheral defocus contact lenses and orthokeratology.