Renal Replacement Therapy (RRT) Overview. Overview of RRT. Renal replacement therapy (RRT) is required when the kidneys are functioning at less than 10â15 percent. Dialysis. People with advanced chronic renal failure (CRF), kidney failure, who have progressed to end-stage renal disease (ESRD) usually require dialysis.
Rod cells are far more numerous than cone cell. Cones cells are far fewer than rod cells. Usually located around the periphery of retina. Usually located in the centre of retina. All rod cells are alike, and do not give colour vision. Cones are of three types: blue, green and red, and give colour vision.
Rods work at very low levels of light. We use these for night vision because only a few bits of light (photons) can activate a rod. Rods don't help with color vision, which is why at night, we see everything in a gray scale. The human eye has over 100 million rod cells. Cones require a lot more light and they are used to see color.