Tetrachromacy class eventually lose two of their four cones. The normal explanation of tetrachromacy is that the organism's retina contains four types of higher-intensity light receptor (called cone cells in vertebrates as opposed to rod cells, which are lower intensity light receptors) with different absorption spectra. This means that the animal may see wavelengths beyond those of a typical human being's eyesight, and may be able to distinguish between colors that, to a normal human, appear to be identical. Species with tetrachromatic color vision may have an unknown physiological advantage over rival species. The goldfish ("Carassius auratus auratus") and zebrafish ("Danio
Macula of retina shown to prevent the disease. After death or enucleation (removal of the eye) the macula appears yellow, a color that is not visible in the living eye except when viewed with light from which red has been filtered. Structures in the macula are specialized for high-acuity vision. Within the macula are the fovea and foveola that both contain a high density of cones, which are nerve cells that are photoreceptors with high acuity. In details, the normal human eye contains three different types of cones, with different ranges of spectral sensitivity. The brain combines the signals from neighboring cones to