Retinal ganglion cells can respond to light independently of rods and cones.

“Then David Berson did the seminal experiment where he went to the brain where the central oscillator, the oscillator that drives circadian rhythm in the brain called the suprachiasmatic nucleus, that has been known for many years to receive retinal input. And he labeled the cells that project there. And then he found that even if you destroy rods and cones, you could get light responses from these cells. So you could imagine he nearly fainted when he saw that these cells can respond independent, completely in the absence of rod and cone input.”