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The dark blue, teal, and gold tapetum lucidum from the eye of a cow Retina of a mongrel dog with strong tapetal reflex. The tapetum lucidum (Latin for 'bright tapestry, coverlet'; / t ə ˈ p iː t əm ˈ l uː s ɪ d əm / tə-PEE-təm LOO-sih-dəm; pl.: tapeta lucida) [1] is a layer of tissue in the eye of many vertebrates and some other animals.
Human eye. The cooperative eye hypothesis is a proposed explanation for the appearance of the human eye. It suggests that the eye's distinctive visible characteristics evolved to make it easier for humans to follow another's gaze while communicating or while working together on tasks. [1] [2] [3]
The preorbital gland is a paired exocrine gland found in many species of artiodactyls, which is homologous to the lacrimal gland found in humans. These glands are trenchlike slits of dark blue to black, nearly bare skin extending from the medial canthus of each eye.
If the eye did not move at all, the person has orthophoria. Most people have some amount of exophoria or esophoria; it is quite normal. If the uncovered eye also moved vertically, the person has hyperphoria (if the eye moved from down to up) or hypophoria (if the eye moved from up to down). Such vertical phorias are quite rare.
The earliest predecessors of the eye were photoreceptor proteins that sense light, found even in unicellular organisms, called "eyespots". [23] Eyespots can sense only ambient brightness: they can distinguish light from dark, sufficient for photoperiodism and daily synchronization of circadian rhythms. They are insufficient for vision, as they ...
They have great eyes and are adept at spotting movements of prey." In other words, hawks see the bigger picture that we often miss from our limited view on the ground.
The pupil of the eye dilates in the dark to enhance night vision. Shown here is a pupil of an adult naturally dilated to 9 mm in diameter in mesopic light levels. The average human eye is not able to dilate to this extent without the use of mydriatics. Nocturnal mammals have rods with unique properties that make enhanced night vision possible.
Human eyes are somewhat distinctive in the animal kingdom in that the sclera is very plainly visible whenever the eye is open. This is not just due to the white color of the human sclera, which many other species share, but also to the fact that the human iris is relatively small and comprises a significantly smaller portion of the exposed eye ...