You want the display to overlay the environment. Contact lenses move with your eyeball - glasses don't. This means that you would need to precisely track the le

You want the display to overlay the environment. Contact lenses move with your eyeball - glasses don't. This means that you would need to precisely track the lenses somehow - probably with an apparatus affixed to your head. => Glasses are preferrable. Regarding genetically engineered eyeballs: what if they get a virus?