The Cuban iguana's eyes have a golden iris and red sclera. Cuban iguanas have excellent vision and the ability to detect shapes and movement at long distances.[18] Sensory cells called "double cones" give them sharp color vision and enable them to see ultraviolet wavelengths.[18] By seeking out locations with more ultraviolet sunlight to bask in, the Cuban iguana optimizes vitamin D production.[2] Cuban iguanas have poor low-light vision, because they have few rods or photoreceptor cells. Like other iguanids, Cuban iguanas have a white photosensory organ on the top of their heads, called the parietal eye.[18] This "eye" has only a rudimentary retina and lens and cannot form images, but it is sensitive to changes in light and can detect movement.[18]