Welcome to Just Answer and thanks for your question. What part of the eye are you talking about? Can you describe the shadows? Do you mean you see shadows in your vision or you see a darker area on some part of your eye?
Thanks for the clarification. This is probably just a floater, whichare thickened gel spots within the vitreous fluid of the eye. However, your ophthalmologist should examine your eye to make sure that is all it is. If you see flashes of light, that may just be because of a detached retina and that is an ophthalmological emergency. By middle age or older, it can also be just mechanical irritation of the photoreceptors of the eye. The important thing is that you need to have it checked to make sure it is insignificant. You can't just assume that it is.
Yes, that is called a floater. The inside of the eye is filled with a gel. As we get older (even 40), some bits of the gel thicken. These thickened bits can float about in the more "liquid" fluid and cause floaters or shadows in our vision as we move our eyes. It is scary the first time it happens. It may also be one of the first signs that we are past our youth :-)
Flashers are another possibility that I mentioned just so you would be aware of the difference between the two.