ABSTRACT
The incidence of myopia is gradually on the rise worldwide, which seriously affects the eye health of teenagers and children, causing enormous loss of socioeconomic benefits. As a result, the prevention and control of myopia is crucial and urgent. In recent years, orthokeratology lens have gradually demonstrated its superiority in the field of myopia prevention and control. At present, the principle of controlling the development of myopia by orthokeratology lens is mainly based on the theory of retinal hyperopia optical defocus, which promotes the shift of hyperopic defocus to myopic defocus in myopic patients to curb the growth of the axial length. The effect of controlling the development of myopia is related to various factors, including the total amount of defocusing, pupil diameter, optical zone design, and lens decentration. The widespread use of orthokeratology lenses will effectively reduce the incidence of myopia in teenagers and children. This paper discusses the principle of controlling the development of myopia by the defocus technique of orthokeratology lenses, and the relationship between the amount of defocusing and the position of the defocusing circle and the effect of myopia prevention and control. A specific review was conducted to clarify the research progress on defocus technique of orthokeratology lens in the prevention and control of myopia.
ABSTRACT
@#Myopia is a common ocular disorder. In recent years, the incidence of myopia presents an increasing trend year by year. Patients with high myopia are at an increased risk for severe visual impairment. The economic and societal impacts of complication associated with myopia are enormous. Therefore, it is essential and imminent for implementing effective myopia control strategies. The results of the current study suggest that uncontrolled axial elongation produced by periphral hyperopic defocus could be one of the possible mechanisms for myopia development, multiple strategies especially optical defocus technology based on this are increasingly becoming part of the mainstream clinical practice in myopia management. This article reviews the principle of optical defocus on myopia control, experimental research on defocus myopia animals, and the latest clinical applications of different optical defocus technologies on myopia control, summarizes the clinical research results of myopia control using progressive addition spectacle lenses, peripheral defocus spectacle lenses, defocus incorporated multiple segments spectacle lenses, orthokeratology contact lenses and multifocal soft contact lenses. It is proposed to provide a new option for the treatment plan to delay the progression of myopia.
ABSTRACT
Objective To observe c-Fos expression in visual cortex of infant rhesus monkeys with myopia induced by hyperopic defocus and preliminarily investigate the possibility of visual cortex participating in myopia. Methods Eight SPF grade healthy infant rhesus monkeys aged 20 to 30 days were randomly divided into hyperopic defocused group and control group,4 monkeys for each group. The monkeys in hyperopic defocused group wore -3 D spectacle lenses. The monkeys in control group wore 0 D lenses. The monkeys' refractive error,corneal topography, vitreous chamber depth were measured at the start of lens wear and at 2,4,6,8,12 weeks post-treatment. At 12 weeks post-treatment,the visual cortex tissues were removed for c-Fos protein measurement by immunohistochemistry and Western blot assays. The results were analyzed semiquantitatively to compare the differences of c-Fos expression between hyperopic defocused group and control group. The use and care of the animals complied with Regulations for the Administration of Affair Concerning Experimental Animals by State Science and Technology Commission. This study protocol was approved by Ethic Committee of Zhongshan Ophthalmic Center ( No. 2013-014). Results After 12 weeks'lens wear,the vitreous chamber elongation amplitude of hyperopic defocused group monkeys was more obvious than that of the control group ([0.93±0.24]mm vs. [0.72±0.09]mm;t=2.292,P=0.047). The decrease of hyperopic degrees of hyperopic defocused group monkeys was more obvious than that of the control group ([-3.23± 1.36]D vs. [-1.55±0.52]D;t=-3.273,P=0.006). The eyes of hyperopic defocused group monkeys appeared a remarkable myopic shift after treatment. The number of c-Fos immunoreactive neurons was less in the hyperopic defocused group than that in the control group,with a statistically significant difference between them ([1 843±191]/mm2vs. [2 296±503]/mm2;t=2.381,P=0.041). Western blot assay showed that the optical density of c-Fos protein in the hyperopic defocused group was significantly less than that in the control group (0.50±0.17 vs. 0.99± 0.22;t=-4.982,P<0.01). Conclusions Hyperopic defocus,as an abnormal visual stimulus,can induce the onset of myopia in infant rhesus monkeys and inhibit c-Fos expression in visual cortex. Visual cortex may participate in myopia induced by hyperopic defocus.