Re: A bit large?
100mm² in the article refereed to the proposed device size for *human* eyes, not the devices already tested in eyes of rats.
So, if we estimate a human eye to be roughly 5-15 x the diameter of a rat eye, and you say the rat test device was 1mm in diameter, 100mm² sounds about right.
Another direction:look at the diagram of a human eye. You know how big your pupil is. Use that to gauge the diameter of the optic nerve, and the way the optic nerve spreads to cover the retina. Now ask yourself how you would imake a device to interface with that nerve; interfacing at the root would be too fiddly, interfacing at the branches would waste surface area of the device.
A device just smaller than a contact lens sounds about the right size.