Eye

"Shut up, kid. Tell me more about my eyes."

– Guinan to Wesley Crusher and William T. Riker, 2365 ("The Dauphin")

"Our eyes reflect our lives, don't they? And yours, so confident."

– Shinzon to Jean-Luc Picard, 2379 (Star Trek Nemesis)

In anatomy, the eye was the organ for eyesight. Most humanoids had two placed evenly in sockets of the skull. Some species had more eyes though, like Trag'tok's species (DS9: "Resurrection"), and an unnamed being at Kukulkan's zoo (TAS: "How Sharper Than a Serpent's Tooth")

All Denobulans had blue-colored eyes. (ENT: "The Breach", "Cold Station 12")

Among Humans, to "see the look in the eyes" was a common phrase meaning to see emotions expressed in them. (ENT: "The Catwalk")

A diagram of the Human eye depicting the location of eye parts was stored in the USS Enterprise's library computer database. This database was accessed by the Talosians in 2254. (TOS: "The Cage")

All Betazoids had black-colored irises. (TNG: "Power Play"; VOY: "Meld")

The drawing "First Contact" by Haley depicts a one-eyed alien making first contact with a Human in an environmental suit. (ENT: "Breaking the Ice")

In 2364, the Aldeans' eyes were very sensitive to bright light due to chromosomal damage. (TNG: "When The Bough Breaks")

When the anaphasic lifeform Ronin was bonded to a Human, the host's eyes turned green. (TNG: "Sub Rosa")

When hasperat was made correctly, it caused the eyes to water. (TNG: "Preemptive Strike")

Martok lost one of his eyes in a fight with Ikat'ika during his two-year confinement at the Dominion's Internment Camp 371. (DS9: "In Purgatory's Shadow", "By Inferno's Light")

Beverly Crusher felt that Data had nicer eyes than B-4. (Star Trek Nemesis)

The loss of eyesight was known as blindness.

Sometimes, when an eye was lost or damaged, one might have elected to wear an eyepatch to cover it. (Star Trek VI: The Undiscovered Country; DS9: "Our Man Bashir"; VOY: "False Profits")

Elim Garak once got a confession out of Doctor Parmak simply by staring at him for four hours. Afterwards, he kept saying "His eyes, his eyes." (DS9: "The Die is Cast")

In the writers' first draft script of ENT: "Dear Doctor", an eye examination was performed by Doctor Phlox on an unnamed Enterprise officer. The procedure involved the crewmember wearing a pair of futuristic-looking goggles, sitting on one of sickbay's biobeds, while Phlox studied an eye examination chart on one of the room's monitors and pressed corresponding buttons on a keypad.