Hmme1rop1zation and late onset myopia. the role of retinal image quality and the accommodation system

Purpose: To explore the interactions between the accommodation s> stem and the mechanisms of emmetropization in humans in order to investigate the aetiology of late onset myopia. Methods: Computer modelling was used to determined the potential interactions of the accommodation control system and a mechanism of emmetropization driven by the image quality of the retinal image. In comparison with previous theories linking accommodation and myopia, the interaction in this model is entirely optically mediated by the blur within the retinal image. The impact of viewing habits, oculomotor parameters affecting accommodation, refractive error and refractive correction were examined. Results: A model incorporating current understanding of the contributions of blur and disparity cues to accommodative accuracy with a simple regulatory growth response driven by retinal image blur successfully demonstrated emmetropization from a variety of initial refractive states. Increased near work produced a tendency towards myopia irrespective of initial refractive error. This model successfully predicted that esophona and reduced blur driven accommodation responses should increase the tendency for late onset myopia to develop as has been noted in human studies Full optical correction of myopia led to an increased myopic shift, a response that could be partially ameliorated with bifocal spectacles. Conclusions: For the first time this model provides a quantitative explanation for the development of late onset myopia. In addition the key epidemiological features of late onset myopia notably the association with esophona and accommodative performance are successfully predicted along with the impact of refractive correction on the progression of late onset myopia. [none].