Is it possible to change brown eyes to green?

No, but you can get different colored contact lenses.

You cannot "Dye" your eyes but you can get Iris implants, and change the color of them permanently. There is a product/procedure called newiris, and it only take a few minutes and can be reversed.

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Yeah, except the NewColorIris treatment is illegal in the US, and for a good reason. It will almost always cause vision problems, cataracts, swollen puffy eyes, etc. And you'll constantly be buying eye drops and such.

Also, it doesn't change your eye color, the implants simply cover it up. And you can always get them removed, back to the original color. Course, the surgery itself costs $7,500 to get done; so you'll be paying that same amount to get em removed if you don't like them.

You can't tattoo your irises, only the white parts. If you want to change your eye color, you only need to wait until they invent a liquid you inject into the iris; to bleed, absorb, and dye it a new color. Or, instead of waiting, invent it yourself!