Eyes are organs of the visual system.
The visual system is the part of the central nervous system which gives organisms the ability to process visual detail as sight, as well as enabling the formation of several non-image photo response functions.
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They provide organisms vision, the ability to process visual detail, as well as enabling several photo response functions that are independent of vision.
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Eyes detect light and convert it into electro-chemical impulses in neurons.
A neuron is an electrically excitable cell that processes and transmits information through electrical and chemical signals.
Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum.
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.
The optic nerve, also known as cranial nerve II, is a paired nerve that transmits visual information from the retina to the brain.
The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals.
Eyes with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system.
Animals are multicellular, eukaryotic organisms of the kingdom Animalia.
Image-resolving eyes are present in molluscs, chordates and arthropods.
An arthropod is an invertebrate animal having an exoskeleton, a segmented body, and paired jointed appendages.
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.
A microorganism, or microbe, is a microscopic organism, which may exist in its single-celled form or in a colony of cells.
A circadian rhythm is a natural, internal process that regulates the sleep-wake cycle and repeats roughly every 24 hours.
From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment and to the pretectal area to control the pupillary light reflex.
The pupillary light reflex or photopupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity of light that falls on the retinal ganglion cells of the retina in the back of the eye, thereby assisting in adaptation of vision to various levels of lightness/darkness.
Intrinsically photosensitive retinal ganglion cells, also called photosensitive retinal ganglion cells, or melanopsin-containing retinal ganglion cells, are a type of neuron in the retina of the mammalian eye.
The pretectal area, or pretectum, is a midbrain structure composed of seven nuclei and comprises part of the subcortical visual system.