First, human eye dynamic range is not that great. It only appears to be better than our current high end cameras, because our brain constantly merges "snapshots" taken using different exposure settings. Our eyes cannot register extremely bright and extremely dark objects simultaneously (even though the brain can). True wonder of image processing, but only mediocre optics/imaging device.
There are several proposals/prototypes showing how the dynamic range of image sensors could be greatly improved:
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each photodiode resets its state upon hitting maximum charge and remembers how many times it happened
Quanta Image Sensor by Eric Fossum
uses much smaller and faster photon-counting pixels instead of "analog" charge containers + A/D converters
