It's true that sunlight can help improving your vision. There is a practice called 'sunning', you can do this practice by letting the sun light on your closed eyelids. Sun on your eyelids allows your eyes to get used to brighter light.
If exposing your closed eyelids to direct sunlight, you will find that your vision is clearer and sharper for Sunlight is also very healing. There is something you need to pay attention: don't look directly into the sun with your open eyes. Close your eye before you point your eyes to the sun and, no contact lenses while you practicing this.
Once you get the right method, you can repeat the exercise so you will be able to longer the time your eyes exposing under the sunlight. It can reduce your eyes' sensitivity to light then your eyesight can improve naturally.
There are more on this website:
To some degree, the sunlight will reverse myopia because of the adjustment of the refraction. Eye is in regulating the stillness of the state, from 5 meters outside of the equal light after eye refractive. The focus is just falling in the retina which can form clear image. It has the refractive state of the eye which is called emmetropia. Its focus falls on the front retina which can't accurately in the retina and form clear image. It is called axial myopia from near to target dispersion ray but highly adaptive capacity. As long as the target to the eyes moves to a certain distance, it can get clear vision. The myopic eyes see far fuzzy to concave spherical lens correction. The sunlight will to some degree make the corneal get the larger content of the light which could reverse myopia. However suitable amount of sunlight is useful. You should also use the eyes in the suitable amount to keep them healthy.
Well, yes, sunlight can be good for myopia, but we cannot say it can cure myopia. First, you should know that myopia occurs when the physical length of the eye is too long, causing light to focus in front of the retina and blurring images. For the causes, some related to inheritance and some to the environment. And according to some experts, by having sunlight, it will just be good for myopia. But on the other hand, it cannot cure myopia. And if you want to cure it, you may need to take eye surgery which can just cure it permanently.