Because it is a highly approachable part of the brain, the retina is by far one of the best known regions of the Central Nervous System. The systematic application of modern neuroanatomical and quantitative techniques has provided the complete catalogue of retinal cells, while electrophysiological experiments are gradually revealing their functions. Retinal complexity is achieved through serial and parallel connections of about 50 different types of neurons. Among retinal circuits, the best known is the rod pathway, a chain of neurons by which rod-generated signals are grafted onto an evolutionary more antique cone system. About ten types of cone bipolar cells provide parallel channels conveying to the brain information related to colour, temporal domain, motion etc. This elegant and complex circuitry becomes severely corrupted in retinal degeneration causing the progressive death of photoreceptors for genetic causes. Retinitis Pigmentosa and related disorders are more than just photoreceptor diseases, as inner retinal cells are severely affected by the loss of their major input neurons.