Peripheral refraction and peripheral eye length in myopic progression and myopic control

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Peripheral refraction and peripheral eye length in myopic progression and myopic control

 

Author: Lee, Tsui Tsui
Title: Peripheral refraction and peripheral eye length in myopic progression and myopic control
Degree: Ph.D.
Year: 2014
Subject: Myopia.
Retina -- Physiology.
Hong Kong Polytechnic University -- Dissertations
Department: School of Optometry
Pages: xviii, 328 pages : color illustrations ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2780672
URI: http://theses.lib.polyu.edu.hk/handle/200/7875
Abstract: A number of animal studies have shown that optical input of hyperopic defocus into the retina other than the foveal area would alter central refractive changes. Some researchers therefore proposed that peripheral refraction might also play a role in the regulation of eye growth in human eyes. However, clinical studies on peripheral refraction have yet provided a conclusive answer to this. Certain myopic control treatments have also been devised in attempt to arrest myopia progression through the manipulation of peripheral refraction of an eye. Because of its ability in reducing and even converting relative peripheral hyperiopia into relative myopia in myopic eyes, orthokeratology (ortho-k) was thought to have exerted its myopic control effect through reducing the hyperopic defocus in the peripheral retina. Despite the extensive work done, it is still unclear how these treatments were able to arrest myopic progression. The current study set out to investigate the characteristics and changes of field curvatures and retinal contour in children eyes which are more prone to refractive changes and in eyes which have undertaken ortho-k treatment. Longitudinal monitoring of peripheral refraction and peripheral eye length were performed on fifty seven untreated children with different ametropia and twenty eight ortho-k-treated children every six-monthly for twelve months. The baseline and 12-month changes in field curvatures and retinal contours were compared between different refractive groups and between eyes with different rate of myopic progression in both untreated and ortho-k-treated subjects. Although significantly different peripheral refraction and retinal contour were found in different ametropias, the current study was unable to find any association between field curvature, retinal contour and myopic progression. Nor there was an association between the changes in these parameters and central refractive changes. Eyes with different rates of myopic progression did not showed significant differences in both parameters, in both untreated and ortho-k-treated subjects. Comparing the field curvature and retina contour in the ortho-k-treated eyes and in the untreated myopic eyes did not find any significant difference. In a pilot investigation with six of the ortho-k-treated eyes, changes in field curvature and retina contour during the spectacle-wearing phase did not differ significantly from those changes during the ortho-k-wearing phase. Therefore, results from the current study did not show that relative peripheral refraction and eye length have potential in the regulation of eye growth. In the current study, we also determine the variability of measurement methods commonly used in current research on peripheral refraction or peripheral eye length. Future studies on the risks factors on eye growth and mechanism of myopic control effect with ortho-k are still need.

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