The retina is the innermost, photosensitive layer of the eye containing the photoreceptor cells — ~120 million rods (for low-light, achromatic vision) and ~6 million cones (for colour and detail vision). The retina also contains bipolar cells, ganglion cells, and other neurons that process visual information before transmitting it via the optic nerve to the brain. The choroid provides blood supply; the sclera is the tough outer protective coat; the iris controls pupil size.