Hi Sein-Tze, thanks for your question! As Hui Qun above mentioned, there is little research that shows the efficacy of eye exercises in preventing or slowing down myopia. Some parents say it does work, and some parents do not think it does work. Although, Dr Wu says that treatments such as orthokeratology and atropine eye drops do garner a lot of efficacy in terms of medical research.
According to this article (http://www.allaboutvision.com/buysmart/see_clearly.htm), there is little or no scientific evidence that shows a relationship between eye exercises and the slowing or reversing of myopia. The article noted that exercises are unable to help change the shape of the eyeball. Therefore, is unlikely that it will help in correcting myopia.