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.
The symptoms of retinal disease follow this pattern in Usher syndrome but may be somewhat different in other conditions discussed later. In all cases, both rods and cones deteriorate, but the timing may be different.