English: Throw a strong beam of light on the edge of the sclerotic, and a curious branched figure will be seen, which is an image of the retinal vessels. The construction of these images, usually called Purkinje's figures, will be understood from the figure. In the eye to the right the illumination is through the sclerotic, and in the one to the left through the cornea. Thus, in the eye to the left, the rays passing through the sclerotic at b″, in the direction b″ c, will throw a shadow of a vessel at c on the retina at b′, and this will appear as a dark line at B. If the light move from b″ to a″, the retinal shadow will move from b′ to a′, and the line in the field of vision will pass from B to A. It may be shown that the distance c b′ corresponds to the distance of the retinal vessels from the layer of rods and cones. If the light enter the cornea, as in the eye to the right, and if the light be moved, the image will be displaced in the same direction as the light, if the movement does not extend beyond the middle of the cornea, but in the opposite direction to the light when the latter is moved up and down. Thus, if a be moved to a′, d will be moved to d′, the shadow on the retina from c to c′, and the image b to b′. If, on the other hand, a be moved above the plane of the paper, d will move below, consequently c will move above, and b′ will appear to sink.