It has been shown that the rod and cone cells of our eyes are related to light sensitive brain cells that exist in a marine worm. This type of worm has not evolved itself much in the last 600 million years. link
So going from brain cells to light-sensitive brain cells would be an intermediate step.
Nikko Tinbergen made these points 70 years ago ~ that ALL animals of ALL types Have the Same Organs or Organelles.
ALL means All.
Unless you have the organs to handle the processes you have no existence.
I think the Darwinian model fails because of this cold, hard fact about "organs" or "organelles". There simply isn't the EVOLUTION of a new organ or organelle to handle a totally new process not found in any other animal over a period of time extending over 600 million years.
Even the most ancient sponges have 70% of the same genes that modern humans have ~ and, essentially, the same organs.
If there's no evolution on the big stuff, then where is it? Seems to me all it may have added is a little whittling around the fundamentals ~ but nothing major!