An afterimage is an image that continues to appear in the eyes after a period of exposure to the original image. An afterimage may be a normal phenomenon (physiological afterimage) or may be pathological (palinopsia). Illusory palinopsia may be a pathological exaggeration of physiological afterimages. Afterimages occur because photochemical activity in the retina continues even when the eyes are no longer experiencing the original stimulus.The remainder of this article refers to physiological afterimages. A common physiological afterimage is the dim area that seems to float before one's eyes after briefly looking into a light source, such as a camera flash. Palinopsia is a common symptom of visual snow. Negative afterimages Negative afterimages are primarily caused by neural adaptation of the cells that carry signals from the retina of the eye to the rest of the brain, the retinal ganglion cells. There is also a small contribution when the eye's photoreceptors, the rods and cones, adapt to overstimulation and lose sensitivity. There is brain contribution as well.Normally, any image is moved over...