retinal rod
any of various photoreceptors in the retina that respond to low light levels, as opposed to retinal cones, which require moderate to bright light for activation. In primates, which have both rods and cones, the rods are excluded from the center of the retina, the fovea centralis. All rods contain the same photopigment, rhodopsin; therefore, the rod pathways do not provide color information. The connections of the rod pathways enhance retinal sensitivity to light, but acuity is relatively poor. See also scotopic vision.