Vision is our dominant sense. The eyes are specialized for the detection of light. The optical apparatus projects an image of our environment onto the back of the eye covered by the retina, a true part of the central nervous system. The retina is a well-layered, approximately 200 μm thick tissue and can be divided into an outer part that harbors the light-sensitive cells—the rod and cone photoreceptor cells—and an inner part that comprises a neuronal network. This network performs the first steps of information processing before the signal is relayed by the retinal ganglion cells to the brain via the optic nerve. A human retina harbors around 120 million rod and 6 million cone photoreceptor cells. Rods are highly sensitive, can respond to single light quanta, and provide vision during night and at twilight. Cones are less sensitive and provide color vision during daylight. Behind the retina, two more layers are located: the retinal pigment epithelium (RPE) and the choroid, a dense network of blood capillaries, which provide nutrients and oxygen to the photoreceptors. The direct exposure of retinal neurons to light can result in damage of the retinal cells, for example, by the generation of free radicals. Protective measures are the absorption of ultraviolet light by the lens, protective pigments in the center of the retina, and continuous renewal of the light-sensitive compartment of the photoreceptor cells.