I’m sure at some point in the future, it will become feasible to design a contact lens which can also act as a computer monitor for the one wearing it.
My question is, how long before such a thing could be done? And are there marketable purposes for such a thing? There would have to be some kind of highly portable controlling mechanism for the associated computer. I don’t see that as a problem–devices the size of a cell phone could do it, or, if we want to go way sci-fi with this, some sort of “implant” could get the job done. 
Anyway, I’m mostly just curious about the tech level question. The “is it useful and marketable” question is also interesting but not as central to my intention in posting here.
-FrL-
And just what is going to image the monitor onto the retina? after all, you’ve got your monitor stuck on the lens that’s doing the imaging.
You can’t get real imaging (the kind that projects an image onto a surface) if the object is closer than one focal length to the lens. Since the contact is sitting right on the cornea, obviously that won’t work. In fact, if the lens is on the cornea, it doesn’t even see that lens, since it’s within the “lens” itself (most of the focusing power of the eye is at the cornea-air interface, not the crystalline lens – that’s used for fine correction and accommodation). It’s conceivable to build a flattened lens, optical path, and monitor into a compact device, I suppose, (they are already making astoundingly compact camera devices) but it would be monstrously complex and I’d worry about it being too bulky to use as a “contact lens”. It would be grotesquely expensive – not by any means disposable – and I suspect it wouldn’t be worth the effort.
I don’t know anything about optics, so it’s difficult for me to understand why you can’t have an image in focus with its source on the lens thats doing most of your focusing for you.
Couldn’t the lens compute exactly how the light of the image its producing should look in order to appear “in focus” to the person using the lens? The reason this sounds plausible to me is the following. There is light emanating from the back surface of the contact lens I’m wearing right now–namely, the light that passed through it from the front and was refracted by the lens. That light, when it reaches my retina, produces an image which appears “in focus” to me. If this is the case, then couldn’t a future sci-fi type contact lens do more than simply refract light, but also add and subtract light, in order to produce the appearance of an image, and have that image, too, appear to be “in focus?”
Alternatively, could you not even just have the lens simply project the appropriate light via lasers to the retina? That’s not what I had in mind in the OP, but would such an approach overcome the problems you were alluding to? (I don’t know because I didn’t quite grasp the problem.) Can there be such lasers whcih would not necessarily damage the eye?
-FrL-