Video monitor in contact lenses--engineering question

I’ve seen it said a few times (once on the SDMB) that one major obstacle to putting a video monitor in a contact lense is that the eye can’t focus on an object that close to it.

I’ve not been able to understand how this presents a problem. Why can’t the contact lense video monitor simply present an array of light that is as if the object being portrayed were several feet away?

In other words, say the lens is to present me with an image of text “floating” (as it were) about ten feet in front of me. If there really were text floating ten feet in front of me, there is a particular array of light that text would produce on the surface of my eye. That light array is what my eye has to work with when it is focussing and doing all the other things it does to process the light array into a signal to send up to my brain. But the existence of the text “out there” is not necessary for the existence of the light array on the surface of my eye. And it seems to me that a contact lense could, in theory, produce exactly the same light array–and that my ocular system could as a result resolve the light array produced by that contact lense into an image that is as of a line of text floating ten feet in front of me.

I can imagine some problems with this stemming from sacades, but that doesn’t seem to be the problem people are talking about when they mention the eye’s need to focus. They seem to be saying that the eye would literally have to focus on the contact lens. That’s the criticism that seems wrong to me.

But is there something I’m missing here? Is my solution to the focussing problem fundamentally mistaken in some way?


>Why can’t the contact lense video monitor simply present an array of light that is as if the object being portrayed were several feet away?
It could. You understand the underlying issue correctly. But there is the practical difficulty that lens systems for making something appear at a big distance also cannot be in the same place as the something.

More accurately, a lens with a positive focal length and having an object at a distance equal to the focal length will, to an observer on the other side, present the appearance of that object at infinite distance. But this simple setup puts a focal length between the lens and the real object, so your contact lens is huge again.

Now, if the video monitor generated directed rays rather than rays that just diverge from every pixel, you could do what you want. Think bold. Think submicrometer dipole antennas in a phased array, transmitting light the way radio antennae do. That would work.

In other words, it doesn’t just matter that the photons hit the right spot on your eye. In fact, it matters almost not at all which spot on your eye the photons hit. What matters is what direction the photons are moving in when they hit your eye. We can build devices that cause photons to be moving in particular directions when they hit your eye, but with present technology, those devices are all way too big and bulky to fit in a contact lens.

Well, there are definitely those who think it will work, as evidenced in this storyin the Daily Mail.