When sunlight enters the eye, it strikes the light-sensitive retina. Remember, the retina is part of the central nervous system (CNS) and is connected to the brain via the optic nerve. The retina contains different types of cells. The photoreceptor cells are sensitive to light. No doubt you’ve heard of rods and cones. These cells are specialized neurons in the human eye. Rods are more sensitive to light and help you see under low-light conditions. They do not process color vision, however. Cones are capable of color vision and are responsible for high spatial acuity. They need more light to produce a correct signal, however, so may find it difficult to process color on a dark night outdoors. The photosensitive ganglion cells in the retina, discovered only in the past decade or so, communicate not only with the master circadian pacemaker or clock located in the brain’s hypothalamus (known as the suprachiasmatic nuclei or SCN) but also impact many other brain areas that are known to be involved in the regulation of several functions including your health.