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:
“What a hero Tom was become now! He did not go skipping and prancing, but moved with a dignified swagger as became a pirate who felt that the public eye was on him.”
—Mark Twain [Samuel Langhorne Clemens] (1835–1910)
“Among twenty snowy mountains
The only moving thing
Was the eye of the blackbird.”
—Wallace Stevens (1879–1955)
“The eye deals with excess more easily than the stomach does.”
—Mason Cooley (b. 1927)