From your description, your son has mild nearsightedness on his right eyes. Usually, 20/20 stands for perfect vision and needn't eyeglasses. And 20/50 means the eye that needs eyeglasses with -1.00 to -1.25 prescription lenses. If you plan to buy one pair to him, you'd take him for an eye check so as to get accurate eye prescription for eyeglasses. But personally, you needn't buy eyeglasses for him since he just has a very mild myopia. It may be corrected if he keep good habit of using eyes and do some eye exercises. Good luck.