A New Paper by Masuda et al: “Arrangement of the Human Trichromatic Cone Mosaic in Peripheral Retina”

A poster/paper (3832/A375) was presented at the ARVO 2008 Annual Meeting “Arrangement of the Human Trichromatic Cone Mosaic in Peripheral Retina” authored by O. Masuda, H. Hofer, J. Carroll and D.R.Williams. I interpret this work extending the imaging methodology developed by the authors (and previously by Roorda et al) to larger retinal eccentricities, as being in some way a response to my repeated requests that this measurement be made. But….who knows?

I humbly submit that their results seem to verify my projection in their finding of a “clumping” of, what they (erroneously) term L and M “cones” at retinal eccentricities of 10 degrees. They note that this represents the first instance where the packing arrangement of cones is distinguishable from randomness, i.e., that a spatial order is observed. Their exact statement “Previous studies have concluded that the packing arrangement of L and M cones near the center of the human fovea is not distinguishable from random in most eyes”. (does this mean that the packing arrangement in “some” eyes is not random? – please supply a reference?).

I believe that the basis for what they are observing follows directly from my observation that is calculated directly from Osterberg’s measurements of retinal morphology showing that the maximum (at this point complete!) degree of spatial order appearing as a motif of eight rods surrounding each cone. This perfect geometric array following Osterberg occurs near this eccentricity (really at 7-8 degrees but they are close enough). The interplay of cones and rods at this eccentricity is not statistical anymore but completely ordered! I have proposed that this octagonal motif forms a fundamental (termed “primary”) mid band (“green” or in their terms an “M cone”) light interaction point on the retina. In my explanation this complete degree of geometric spatial order translates into the peak of intensity of the primary mid band wavelength and forms the 550 nm wavelength mid band reference point on the retinal surface. I have proposed that the identification of this geometric reference forms the basis for the color constancy of vision. The eye interprets the exact middle of the visual band geometrically! The retina is not a spectrometer!

I will not go into this much further only noting that the sample size of their images is so small that the statistical nature of the distribution of cones and rods is seen (Osterberg again!). This is as to be expected and they note this. The first degree of order (or “clumping”) that they observe at the 10 degree eccentricity in these statistically small images represents the “tip of the iceberg” of the spatial order that exists at this eccentricity. Their quest for an ordered “mosaic” on the retina, and any idea as to how the randomness that they have observed (until now!) could lead to an image formation mechanism, totally eludes me. I would like to see the reasoning behind this?

The spatial resolution of their imaging methodology and the question why they do not observe rod receptors? I have addressed this in a previous Comment. Suffice it to note that they claim 2 micron resolution which would be approximate the diameter of the inner segment of a single cone and should be sufficient to image rods .

Again, I would claim what they are actually imaging at this eccentricity is a motif of eight rods around each cones. This “M cone” should be really be termed an “M wavelength detection center”

Added on 5/14/08

The authors also undertake a curious (to me) effort to measure the distances between cones apparently to verify the randomness of the distribution. I do not understand why they apparently want to verify what already is, and should be, apparent as the statistical randomness following from the Osterberg morphology data? Their words: “We evaluated the packing arrangement of the 3 cone classes by comparing frequencies of distances between all cones of the same type with those expected based on a random pigment assignment rule”

To be clear – the foveal region that contains > 99% of cones on the retina, and where they want to see a differentiation of these cones into “classes”, is totally “L wavelength” sensitive. Then as rod receptors begin to intrude into the receptor array at the edge of the fovea at eccentricities of one degree a statistical distribution of L and a few M (cone/rod appositions) begins to be seen. At this point if one does not want to believe the data of Osterberg see the figures of George Wald! The author’s measurements until this paper were made at eccentricities of one degree and they observe exactly what they should observe. I would note on the subject of “S” or blue sensitive “cones”, again statistically, here and there an apposition of two adjacent rods will be observed ..and voila, an “S” cone! This is the explanation for the strangely small density of this type of “cone”.

My finding of the three primary wavelength peaks on the retina follows from a simple counting of receptor appositions using Osterberg’s morphology data. Any grad student could do a statistical analysis of the presence of rod/rod appositions in near foveal region (at an eccentricity of one degree as measured by Roorda) and I project that the density so calculated would correspond to these measurements of “S Cones”.

Respectfully submitted.

GCH

5/14/08