Cornea

Definition

The transparent, non-cellular outer layer of the eye that covers the optical structures beneath and serves as the primary refractive surface for focusing light. In arthropods, the cornea forms the outer facet of each ommatidium in compound eyes and the dome of simple eyes (ocelli), consisting of cuticle specialized for light transmission without compromising structural integrity.

Etymology

From Latin cornea (tela) 'horny (web, tissue)', referring to its tough, transparent quality resembling horn.

Example

In the compound eye of a dragonfly, each hexagonal cornea acts as a lens, focusing light onto the underlying crystalline cone and rhabdom to form a neural superposition image.

Related Terms

• Ommatidium
• Facet
• crystalline cone
• Rhabdom
• ocellus
• Cuticle
• dioptric apparatus
• compound eye

Usage Notes

In arthropod morphology, 'cornea' specifically denotes the cuticular lens structure, distinguishing it from the cellular retina beneath. The plural 'corneas' is standard for multiple eyes or optical units; 'corneae' appears in some classical anatomical texts but is rare in entomological usage. Contrast with 'lens' in vertebrate eyes, which is cellular and internal rather than cuticular and external.