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.
Famous quotes containing the word eye:
“And all my days are trances,
And all my nightly dreams
Are where thy dark eye glances,
And where thy footstep gleams
In what ethereal dances,
By what eternal streams.”
—Edgar Allan Poe (18091849)
“Men are to be guided only by their self-interests. Good government is a good balancing of these; and, except a keen eye and appetite for self-interest, requires no virtue in any quarter. To both parties it is emphatically a machine: to the discontented, a taxing- machine; to the contented, a machine for securing property. Its duties and its faults are not those of a father, but of an active parish-constable.”
—Thomas Carlyle (17951881)
“The eye is the best of artists.”
—Ralph Waldo Emerson (18031882)