<unk> s 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.<unk> s detect light and convert it into electro-chemical impulses in neurons. In higher organisms, the<unk>  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<unk>  via the optic nerve to the visual cortex and other areas of the brain.<unk> s with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system. Image-resolving<unk> s are present in molluscs, chordates and arthropods. The most simple<unk> s, pit<unk> s, are<unk> -spots which may be set into a pit to reduce the angles of light that enters and affects the<unk> -spot, to allow the organism to deduce the angle of incoming light. From more complex<unk> s, 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.
Eye
Head
Mouth
Earmold
Skull
Hand
Canthus
Globe 