"Dr. Swaroop summarized the biology of photoreceptors. In humans, rods outnumber cones 20:1 (106 million rods to 5-6 million cones). Photoreceptors are highly metabolically active, with the outer segments regenerated every 10 days. Stringent control of differentiation and homeostasis isrequired for functional maintenance, and dysfunction or death of photoreceptors leads to vision loss. Rods degenerate and die first; cones are like queen bees and rods are like the soldiers. Rods and cones descend along lineages from shared retinal neuroepithelial progenitor cells"