Higher order aberrations, refractive error development and myopia control: a review

Evidence from animal and human studies suggests that ocular growth is influenced by visual experience.Reduced retinal image quality and imposed optical defocus result in predictable changes in axial eye growth.Higher order aberrations are optical imperfections of the eye that alter retinal image quality despite optimal correction of spherical defocus and astigmatism.Since higher order aberrations reduce retinal image quality and produce variations in optical vergence across the entrance pupil of the eye, they may provide optical signals that contribute to the regulation and modulation of eye growth and refractive error development.The magnitude and type of higher order aberrations vary with age, refractive error, and during near work and accommodation.Furthermore, distinctive changes in higher order aberrations occur with various myopia control treatments, including atropine, near addition spectacle lenses, orthokeratology and soft multifocal and dual-focus contact lenses.Several plausible mechanisms have been proposed by which higher order aberrations may influence axial eye growth, the development of refractive error, and the treatment effect of myopia control interventions.Future studies of higher order aberrations, particularly during childhood, accommodation, and treatment with myopia control interventions are required to further our understanding of their potential role in refractive error development and eye growth.The prevalence of myopia has dramatically risen over the past 60 years 1 with significant regional variations in myopia prevalence across the world, from approximately 15 per cent of adults in Australia, 2 to 70-90 per cent in South East Asian countries such as China 3 , South Korea, 4 Singapore, 5 and Taiwan. 6By 2050, it is estimated that 50 per cent of the global population will be myopic (> -0.50 D), with onefifth of these being highly myopic (> -5.00 D). 7 The numerous sight-threatening ocular conditions that are associated with myopia, including retinal detachment, 8 myopic maculopathy, 9 glaucoma, 10 and cataract, 11 represent a significant public health concern both in terms of the global economy 12 and the visual consequences of these ocular pathologies. 13ile the aetiology of refractive error is multifactorial, 14 evidence from animal studies suggest that visual experience is an important factor in eye growth regulation. 15Higher order aberrations (HOAs), defined as optical aberrations that remain following the optimal correction of defocus and astigmatism with conventional sphero-cylindrical lenses, can significantly influence retinal image quality, 16 the accommodation response of the eye, 17 and the relative focal plane of different regions of the entrance pupil. 18erefore, there are various mechanisms through which they may play a role in guiding eye growth and the development of refractive errors.This review summarises the literature examining HOAs in animal models of refractive error development and changes in the HOA profile in humans with age, refractive error, abnormal visual development and various myopia control interventions.Additionally, possible mechanisms linking HOAs with refractive error development and the treatment effect of myopia control interventions are discussed in detail. VISUAL REGULATION OF EYE GROWTHDuring infancy and childhood, structural changes occur within the eye to minimise refractive error.Axial length increases proportionately to a decrease in the dioptric power of the optical components of the eye, which suggests biological, passive regulation of eye growth, 19 a process termed emmetropisation. 20Refractive errors are primarily determined by axial length changes 21 that are disproportionate to the change in the ocular refractive power, where a slowed and increased rate of axial eye growth results in hyperopia and myopia, respectively, due to a failure in emmetropisation. 22posure of the eye to different visual experiences can disrupt emmetropisation, which suggests that the eye also uses visual input to actively influence eye growth in humans. 23