The eye was the primary visual organ of most biological lifeforms, comparable to the photoreceptors used by droids and cyborgs.[source?] The outer coat enclosing the eyeball was referred to as the sclera. Most sentient species in the multiverse fared with a set of two eyes, most notably Humans and their sub-species. In most species, the eye worked by directing light onto the optic nerve by means of a lens, and was protected by an eyelid designed to remove foreign objects and shade against bright lights. There were many variations.