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:
“Show me no more those snowy breasts
With azure riverets branched
Where, whilst mine eye with plenty feasts
Yet is my thirst not staunched;
O Tantalus, thy pains ne’er tell,
By me thou are prevented;
‘Tis nothing to be plagued in Hell,
But thus in Heaven tormented.”
—Michael Drayton (1563–1631)
“People forget that it is the eye that makes the horizon, and the rounding mind’s eye which makes this or that man a type or representative of humanity with the name of hero or saint.”
—Ralph Waldo Emerson (1803–1882)