Cone dystrophy is an inherited ocular disorder characterized by the loss of cone cells, the photoreceptors responsible for both central and color vision. COMMON SYMPTOMS Vision Loss (age of onset ranging from the late teens to the sixties) Sensitivity to bright lights Poor Color Vision Patients see better at dusk and have progressive difficulty with daytime vision. Visual acuity usually deteriorates gradually, but it can deteriorate rapidly to 20/200. Later, in more severe cases, it drops to counting fingers vision. Color vision testing using color test plates reveals many errors on both red-green and blue-yellow plates.