Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and convert it into electro-chemical impulses in neurons (neurones). 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 most simple eyes, pit eyes, are eye-spots which may be set into a pit to reduce the angle of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light. 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. Overview
Complex eyes distinguish shapes and colours. The visual fields of many organisms, especially predators, involve large areas of binocular vision for depth perception.
They may have been expressed in ciliary cells of larval eyes, which were subsequently resorbed into the brain on metamorphosis to the adult form. C-opsins are also found in some derived bilaterian-invertebrate eyes, such as the pallial eyes of the bivalve molluscs; however, the lateral eyes (which were presumably the ancestral type for this group, if eyes evolved once there) always use r-opsins. Cnidaria, which are an outgroup to the taxa mentioned above, express c-opsins—but r-opsins are yet to be found in this group. Incidentally, the melanin produced in the cnidaria is produced in the same fashion as that in vertebrates, suggesting the common descent of this pigment. Additional images
See also
Adaptation (eye) (night vision)
Emission theory (vision)
Eye color
Eye development
Eye disease
Eye injury
Eye movement
Eyelid
Nictitating membrane
Ophthalmology
Orbit (anatomy)
Simple eye in invertebrates
Tapetum lucidum
Tears

Notes
References
Citations
Bibliography
Ali, Mohamed Ather; Klyne, M.A. (1985). Vision in Vertebrates. New York: Plenum Press. ISBN 978-0-306-42065-8. Further reading
Yong, Ed (14 January 2016). "Inside the Eye: Natures Most Exquisite Creation". National Geographic. External links

Evolution of the eye
Anatomy of the eye – flash animated interactive. (Adobe Flash)
Webvision. The organisation of the retina and visual system. An in-depth treatment of retinal function, open to all but geared most towards graduate students. Eye strips images of all but bare essentials before sending visual information to the brain, UC Berkeley research shows