Eye

Eye

Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptor cells in conscious vision connect light to movement. In higher organisms the eye is a complex optical system which collects light from the surrounding environment, regulates its intensity through a diaphragm, focuses it through an adjustable assembly of lenses to form an image, converts this image into a set of electrical signals, and transmits these signals to the brain through complex neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of the brain. Eyes with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system. Image-resolving eyes are present in molluscs, chordates and arthropods.

The simplest "eyes", such as those in microorganisms, do nothing but detect whether the surroundings are light or dark, which is sufficient for the entrainment of circadian rhythms. From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment.

Read more about Eye:  Overview, Evolution, Types of Eye, Relationship To Life Requirements, Visual Acuity, Perception of Colors, Rods and Cones, Pigmentation

Famous quotes containing the word eye:

    The gods are partial to no era, but steadily shines their light in the heavens, while the eye of the beholder is turned to stone. There was but the sun and the eye from the first. The ages have not added a new ray to the one, nor altered a fibre of the other.
    Henry David Thoreau (1817–1862)

    A squirrel leaping from bough to bough, and making the wood but one wide tree for his pleasure, fills the eye not less than a lion,—is beautiful, self-sufficing, and stands then and there for nature.
    Ralph Waldo Emerson (1803–1882)

    America is a hurricane, and the only people who do not hear the sound are those fortunate if incredibly stupid and smug White Protestants who live in the center, in the serene eye of the big wind.
    Norman Mailer (b. 1923)