|Title:||Peripheral refraction, central retinal function and thickness in children with myopia development|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Eye -- Refractive errors
|Department:||School of Optometry|
|Pages:||xvii, 140 pages : color illustrations|
|Abstract:||Myopia is reaching epidemic proportions with its increasing prevalence, especially in East and Southeast Asia. It is a multifactorial disorder. Findings in animal models with deprived non-foveal visual experience provided an insight about the role of peripheral image quality on central refraction development. Clinical human studies have demonstrated that refractive error varies with retinal eccentricity and different ametropic groups have distinct peripheral refractive error profiles. Longitudinal studies in children, however, were not able to establish a predictive role of peripheral refractive error on myopia onset or progression. It seems that the effect of peripheral refractive error alone cannot trigger or fully explain the myopia development mechanism in children. Ample evidence from research using multifocal electroretinogram (mfERG) implies that myopia results in impaired retinal function. It was demonstrated that the severity of myopia in adults was negatively associated with mfERG responses, retinal adaptation responses and inner retinal function. Discrepancies of mfERG response characteristics between myopic adults and children were also observed. Findings of recent longitudinal studies have also indicated that central retinal function might be associated with myopia development in children. However, investigation of the relationship between retinal electrophysiology and myopia development is limited and further study on the role of retinal function would provide new insight in the understanding of myopia. Ocular structural changes in myopia have been observed in animal models, and a direct relationship between retinal thickness and the severity of myopia was reported. With the application of optical coherence tomography in vivo imaging, clinical studies have revealed that children with moderate myopia tended to have smaller total macular volume and thinner quadrant-specific macular thickness, indicating that early anatomical changes are present in the retina of myopic children. Further studies are required to understand how the relationship between retinal function and structure evolves along with myopia development. This 3-year longitudinal study aims to demonstrate the changes of retinal electrophysiological function, peripheral refraction, and central retinal thickness associated with myopia development in children; to investigate the role of peripheral refractive error, retinal electrophysiological function, and central retinal thickness on juvenile myopia development; and to determine whether the retinal electrophysiological function, peripheral refraction, and central retinal thickness are possible precipitants of myopia development in young children aged 6 to 9 years.|
106 subjects with emmetropic refractive errors were recruited at baseline visit and 88 subjects completed all four visits of the study. Cycloplegic objective central refractive errors changed from emmetropia at baseline visit to mild myopia at the last visit, with a concurrent axial elongation. Together with the central refraction change, peripheral refraction changed to become more myopic, while the relative peripheral refraction tended to more hyperopic. The electro-retinal activities showed significant changes over time, and the trends of changes were different in terms of retinal regions. Global Flash (MOFO) mfERG responses from the central retinal region displayed a significant decrease in amplitude and delay in implicit time. The response from other retinal regions also showed significant decreases in amplitude, but there were no changes in implicit time. However, with respect to retinal structure, central retinal thickness had no significant change over the study period. At the early stage of juvenile myopia development, the peripheral refraction (optics) and electro-retinal activities (function) change over time, while the central retinal thickness (structure) is relatively preserved. Subjects in our study were retrospectively divided into Emmetropic, Low Myopic and Moderate Myopic subgroups based on their central cycloplegic objective refraction at the last visit. The myopic groups displayed trends to have more peripheral hyperopic changes, delayed and decreased central retinal responses at baseline, and quadrant-specific thinning of outer macular thickness than those observed in the emmetrope group. Overall the results from our longitudinal study suggest that marked variance of retinal function and structure are noted earlier than that of retinal optical changes in myopia progression, which leads to the possible predictive role of central retinal function and structure in juvenile myopia development. We demonstrated that the baseline amplitude of central induced component of mfERG response, which originates from the inner retina, was consistently correlated with subsequent myopic refraction changes and axial elongation in young children. This mfERG parameter was measured in emmetropic children with normal visual acuity, good ocular health, and within normative range of central retinal thickness, indicating that long-standing myopia effects, with respect to either pathological or structural changes in retina, could not account for the variance of the parameters obtained. Therefore, we hypothesize that the central inner retina is an essential determinant of the visual feedback process, where the peripheral retinal input could be decoded, and play a commanding role in the manipulation of juvenile myopia development. In summary, emmetropic children with subclinical decrease of inner retinal function, together with specific-quadrant thinning of the central retina, are more likely to develop myopia with faster progression.
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