The eye, at its primitive form, served functions such as light detection, shading with dark pigment to sense light direction, and a connection to motor structures for light-responsive movement. While some organisms perform all three functions in one cell, the two-celled eye is widely recognized as the simplest accepted structure. The evolution of eyes started with the basic photoreceptor-pigment cell structures to complex eyes with muscle connections, lenses, and improved optics. An increased number of photoreceptors provided images with more details (22).