Vision is the only photo responsive sense. Visible light travels in waves and is a very small slice of the electromagnetic radiation spectrum. Light waves differ based on their frequency (wavelength = hue) and amplitude (intensity = brightness).
In the vertebrate retina, there are two types of light receptors (photoreceptors): cones and rods. Cones, which are the source of color vision, exist in three forms—L, M, and S—and they are differentially sensitive to different wavelengths. Cones are located in the retina, along with the dim-light, achromatic receptors (rods). Cones are found in the fovea, the central region of the retina, whereas rods are found in the peripheral regions of the retina.
Visual signals travel from the eye over the axons of retinal ganglion cells, which make up the optic nerves. Ganglion cells come in several versions. Some ganglion cell axons carry information on form, movement, depth, and brightness, while other axons carry information on color and fine detail. Visual information is sent to the superior colliculi in the midbrain, where coordination of eye movements and integration of auditory information takes place. Visual information is also sent to the suprachiasmatic nucleus (SCN) of the hypothalamus, which plays a role in the circadian cycle.
(cd) unit of measurement of luminous intensity (brightness)
describes a time cycle about one day in length
weakly photosensitive, chromatic, cone-shaped neuron in the fovea of the retina that detects bright light and is used in daytime color vision
transparent layer over the front of the eye that helps focus light waves
region in the center of the retina with a high density of photoreceptors and which is responsible for acute vision
(also, farsightedness) visual defect in which the image focus falls behind the retina, thereby making images in the distance clear, but close-up images blurry
pigmented, circular muscle at the front of the eye that regulates the amount of light entering the eye
transparent, convex structure behind the cornea that helps focus light waves on the retina
(also, nearsightedness) visual defect in which the image focus falls in front of the retina, thereby making images in the distance blurry, but close-up images clear
visual defect in which the image focus falls behind the retina, thereby making images in the distance clear, but close-up images blurry; caused by age-based changes in the lens
small opening though which light enters
layer of photoreceptive and supporting cells on the inner surface of the back of the eye
main photopigment in vertebrates
strongly photosensitive, achromatic, cylindrical neuron in the outer edges of the retina that detects dim light and is used in peripheral and nighttime vision
paired structure in the top of the midbrain, which manages eye movements and auditory integration
cluster of cells in the hypothalamus that plays a role in the circadian cycle
in a neuron, slight continuous activity while at rest
sense of sight