The human retina has an area of about 1000 mm^2. If we have a total of 125 million rods and 6.5 million cones in each eye, show that we have about 131,500 sensory cells per square millimeter in the retina.
Since the number of transducers, rods and cones, become less as you approach the periphery of the eye, with the fovea having the greatest density of cells, I would not know how to do it. However,
(125,000,000 + 6,500,000)/1000 = 125,000 + 6,500 = 131,500