Gene therapy of the human retina levels of light. What follows often is the death of cone cells, responsible for color vision and acuity, at light levels present during the day. Loss of cones leads to full blindness as early as five years old, but may not onset until many years later. There have been multiple hypotheses about how the lack of rod cells can lead to the death of cone cells. Pinpointing a mechanism for RP is difficult because there are more than 39 genetic loci and genes correlated with this disease. In an effort to find the cause of RP, there have been different
Evolution of the eye focal length of an early lobopod with lens-containing simple eyes focused the image "behind" the retina, so while no part of the image could be brought into focus, the intensity of light allowed the organism to see in deeper (and therefore darker) waters. A subsequent increase of the lens's refractive index probably resulted in an in-focus image being formed. The development of the lens in camera-type eyes probably followed a different trajectory. The transparent cells over a pinhole eye's aperture split into two layers, with liquid in between. The liquid originally served as a circulatory fluid for oxygen, nutrients, wastes,