The retina was a tissue lining the inner surface of the eye.
A member of the Cabal examined by Phlox in 2151 had compound retinas, allowing him to see better than many sensors. (ENT: "Broken Bow")
In 2153, Malcolm Reed was left with a detached retina following a fight with Major Hayes. (ENT: "Harbinger")
In 2367, the Cytherian probe emitted an intense flash of light which knocked Reginald Barclay unconscious, but Geordi La Forge was unaffected because his VISOR acted as a filter. Doctor Beverly Crusher determined that Barclay's retina was undamaged. (TNG: "The Nth Degree")