It is often said that our retinas are are an example of sub-optimal design.
A few years ago I was intrigued by a passing comment in one of Nick Lane's to the effect that this is not a good argument but he didn't go into much detail.
Researchers at Leipzig have revealed the role of glial cells in transmitting light from the surface of the retina to the cones, acting like fiber-optic cables.
Erex Ribak has built a model of the eye and demonstrated some fascinating details...
So, the question is - does this reflect good "design" or a retro-fitted repair like the Hubble Telescope's glasses?