Retinas

Part of speech: noun

Definitions

1. The layers of light-sensitive cells at the back of the eye that convert light into neural signals
2. The part of the eye responsible for visual perception, containing photoreceptor cells
3. The sensory tissues within the eye where images are focused and processed before transmission to the brain

Etymology: The retina is named for a net, and the name began as a description of blood vessels rather than of light. Galen, the Greek physician of the second century, called the layer amphiblēstroeidēs chitōn, a "net-like tunic," and the Arabic medical tradition rendered it as a "net-like layer" (ṭabaqa shabakiyya). The Latin tunica rētīna, "net-like tunic," was a later translation, and the English word came from it. The name was first applied to the network of vessels at the back of the eye, which resembled a fine mesh, and only later to the light-sensitive tissue that lies beside them. Medieval writers in Latin used the shortened form rētīna by the twelfth century, and the word reached English in Middle English as rethina. The meaning had shifted before the anatomy was understood, so the word describes a net the eye's photoreceptors do not resemble at all.

Synonyms: eye layers, light-sensitive tissues