Compound eyes

Definition

A visual organ composed of many discrete optical units called ommatidia, each with its own cornea, lens, and photoreceptor cluster. The array produces a mosaic image from thousands of slightly divergent viewpoints, trading fine resolution for panoramic coverage, high temporal acuity, and— in many insects— sensitivity to polarized light. Found in most adult insects, crustaceans, and some other arthropods; typically absent or reduced in arachnids, which possess simple eyes.

Etymology

Latin componere (to put together) + oculus (eye), referring to the assembled nature of the structure

Example

The compound eyes of male horseflies (Tabanidae) can cover most of the head and contain up to 10,000 ommatidia, enabling rapid pursuit of females in flight.

Synonyms

• faceted eyes

Related Terms

• Ommatidium
• simple eyes
• Cornea
• Rhabdom
• flicker fusion frequency
• polarization vision
• superposition eye
• apposition eye

Usage Notes

Specialists distinguish apposition compound eyes (common in diurnal insects, each ommatidium isolated by pigment) from superposition eyes (typical of nocturnal insects and crustaceans, where light from multiple ommatidia converges on shared photoreceptors). Resolution is measured by the inter-ommatidial angle; acuity is thus coarser than vertebrate camera eyes but motion detection is superior. Do not confuse with 'clusters of simple eyes' seen in some arachnids.