A STROLL ACROSS THE RETINA – AN ALLEGORY

This story is based on the well known measurements made by G. Osterberg, “Topography of the Layer of Rods and Cones in the Human Retina”, Acta. Opthalmologica (suppl.) 6, 1-103, 1935 and repeatedly used everywhere

I find myself standing at the center of a shallow bowl shaped arena.  A bright light shines down from a dome above and it must be sometime around noon because the light emanates from that position in the sky overhead.  The floor under my feet seems to be composed of an array of round  transparent glass-like tiles that I note randomly emit flashes of red light between them. These flashes do not come from any single tile but seem to connect pairs of the circular tiles that comprise the floor.  I further note that all of the flashes seem to be of exactly the same shade of red.

I am in a mood to explore, so I proceed to walk outward along what must be a radius of my  broad  concave environment.  At first, all of the tiles under my feet continue to be of the same diameter emitting the same random red flashes of light. Upon close inspection I see that the light does not come from the interior of the tiles but rather emanates from the periphery. In the tiles themselves there seems to be a “dance of particles” as is iron filings were continually being jostled  by a magnetic field.  After walking a distance, however, I encounter here and there the same type of random flashes but these are green in color!  The green flashes emanate from one of the round tiles I mentioned before and a new smaller tile that is being introduced at random into the array.

Continuing my walk I note that the green flashes are increasing in number in the still preponderant sea of red. Finally,  I reach a point where all flashes are green and the red has completely disappeared. Stranger still, I note that flashes of blue (!) light are appearing here and there, triggered by the, what has become obvious, even rarer encounter of two of the smaller tiles.   Continuing my journey toward the edge of the bowl, I find that the number of green flashes now begins to diminish with the blue variety beginning to dominate until, finally, the floor is composed of an almost complete sea of blue flashes.

Summarizing my experience in traversing the retinal surface, I have passed through three somewhat overlapping regions starting from an initial red at the center, through a region of green to, finally, a periphery that is entirely blue. I recall that these are what I was taught as being the “primary” colors from which the other hues of color are synthesized. Focusing on the green region that I have passed through, I reason that the increase and then decrease in the density of green flashes as I walk outward from the center must represent an intensity peak of this color. I reason that since the bowl of the retina is circularly concave each of these regions must represent concentric rings of the three colors on the retinal surface. I reason therefore that this surface cannot be, as has for so long been thought, the analogue of the film plane of a camera or any of the other contemporary imaging devices that we use that would comprise some sort of ordered array of color centers to detect an image. Rather, it seems that the retina must certainly be a diffractive surface.

To be continued………

GCH