To the Editor.
—In the December 1987 issue of the Archives, Roy and coworkers1 accurately identify blue-yellow color vision defects in patients with sickle cell anemia using the specific and sensitive Farnsworth-Munsell 100-hue test in a well-designed, case-control study. Their interpretations of this finding, however, are not entirely accurate. This is not an unexpected finding, as they claim, and it is not useful in evaluating central vision functions in patients with sickle cell anemia, as they suggest.Normal human color vision is trichromatic, and is mediated by three different types of cone. The red and green cones, which number approximately 6 million, are concentrated heavily in the macular region; the blue cones, which number less than 1 million, are scattered evenly in a coarse mosaic throughout the retina, and are not found in the fovea at all.Blue cones are more vulnerable to retinal injury than the red and
MacKay CJ. Color Vision Defects in Retinal Disease. Arch Ophthalmol. 1989;107(6):790. doi:10.1001/archopht.1989.01070010812006