ommatidium
/ˌɑməˈtɪdiəm/
noun
- One of the many tiny, individual light-sensitive units that together form the compound eye of insects, crustaceans, and some other arthropods.
- Each ommatidium in a fly's eye captures a small piece of the visual field.
- The number of ommatidia in a dragonfly's eye can reach tens of thousands.
- When light hits an ommatidium, it sends a signal to the insect's brain.