Evolution of the Eye

I may be way in over my head here but something occured to me about one of Fred's posts. It has been pointed out on several occasions that the mammalian eye is far from perfect. In fact some of the features could be considered "deleterious". For instance the rods and cones facing in the opposite direction of incident light leading to nerve fibers passing in front of incident light leading to a large blind spot.So, one doesn't have to assume a 100% beneficial mutation rate. A higher deleterious mutation rate serves to decrease the efficiency and may not reduce the functionality.