1 [ret-n-uhl]
of or pertaining to the retina of the eye.

1830–40; retin(a) + -al1 Unabridged


2 [ret-n-al, -awl]
noun Biochemistry.
an orange pigment, C 2 0 H 2 8 O, that is the active component of rhodopsin and is liberated upon the absorption of light in the vision cycle; vitamin A aldehyde.
Also, retinene [ret-n-een] .

1940–45; retin(a) + -al3 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
retina (ˈrɛtɪnə)
n , pl -nas, -nae
the light-sensitive membrane forming the inner lining of the posterior wall of the eyeball, composed largely of a specialized terminal expansion of the optic nerve. Images focused here by the lens of the eye are transmitted to the brain as nerve impulses
[C14: from Medieval Latin, perhaps from Latin rēte net]

retinene or retinal (ˈrɛtɪˌniːn, ˈrɛtɪnəl)
the aldehyde form of the polyene retinol (vitamin A) that associates with the protein opsin to form the visual purple pigment rhodopsin
[C20: from retina + -ene]
retinal or retinal
[C20: from retina + -ene]

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Medical Dictionary

retinal ret·i·nal (rět'n-āl', -ôl')
See retinaldehyde.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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Example sentences
In vertebrates this protein is found in retinal cells, where it transduces the
  energy of light into a nerve signal to the brain.
Claims the market for a successful retinal prosthesis is significant.
Visual pigments are found in specialized retinal cells at the back of the eye.
The technique is not suitable for blindness caused by retinal damage.
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