There are few exercises that helps health improvement and those exercise can't be explained in a Scientifically manner but the result is really awesome / positive, beyond the imagination of Scientists.
I too have heard that walking on Green grass can improve our vision and reduce the spec number etc. but who will actually, practically and continuously doing it?
To improve your eyesight from bad to good is, few suggestion I came across and sharing with all of you.
Avoid too much salty items
Slightly rub on eyelashes daily as an exercise
Divert your vision to a different place often
Sleep ontime and make sure your eyes never strain
Don't use very hot water to shower
Don't watch the thing that glare your eyes
Do not eat much fatty items like Mayonnaise though it is preparing from egg, fat and oil etc.