Photoreceptor (Earth-2042)

Photoreceptors is a generic name for the optical sensors of a droid. They are the equivalent to an eye. Numbers of photoreceptors can vary depending on the size and model of a droid. For instance, R2-D2 has one, while EV-9D9 has three. Many droids, like C-3PO, has two. Some can have them in different areas. For instance, General Grievous' magnaguards had a built-in one in their torso to enable them to fight without their heads.

Source

 * https://starwars.fandom.com/wiki/Photoreceptor