I worked on a 'virtual eyeball' to create images that somewhat model the signals going to the brain.
Since the the eye has more receptors in the center of it, the center is sharper and more detailed. The color channels (gray-tones were eleminated) are half the resolution since the human eye has less receptors for colors than for brightness.
I used a barrel distortion formula which I altered a bit to get the center sharp while the edges are heavily bended.
First screenshot of the eyeball system:
The original microscopy-image was made by Norman Reppingen in 2007 (found by google: http://www.mikroskopie.de/mikforum/read.php?2,30983,30983#msg-30983).