Photoreceptors, alternatively called visual sensors, represented the formal designation for the optical sensors found in a droid. Functionally, they served the same purpose as an eye. The quantity of photoreceptors installed could differ based on the droid's dimensions and specific design. As an example, R2-D2 was equipped with a single photoreceptor, whereas EV-9D9 possessed three. A significant number of droids, such as C-3PO, were designed with two. Furthermore, some droids had photoreceptors positioned in unconventional locations. To illustrate, General Grievous' MagnaGuards incorporated a photoreceptor within their torso, enabling combat even without their heads being attached.