Rethinking the Process of Vision

Please read this paper (J. Opt. Soc. Am, Vol.57, No.11, November 1967). The retina described by Wald corresponds almost exactly to the retinal response of my explanation by making the simple substitution of the term“rod-rod appositions” for “blue-sensitive cones”.

Even his opening paragraph:

“In 1894 Konig and Kottgen reported experiments designed to show that the central region of the normal human fovea is blue blind (with reference). Konig had come to believe the sensation of blue is excited by rods…..”

One should also read George Wald’s Nobel Lecture at noting his Figure 15 that defines retinal response very much as I explain.

http://nobelprize.org/nobel_prizes/medicine/laureates/1967/wald-lecture.pdf

At the risk of being accused of taking Wald’s thoughts out of context I will transcribe some sections of his text. I believe that these summarize the thrust of the paper.

From the Abstract (p.1289):

“The blue cone system falls in sensitivity from the border of the photopic zone – the functionally all-cone areas – to a minimum, usually to extinction, at it’s center”…”Also the red – and green cone systems display the opposite gradient; their sensitivities decline regularly from the center toward the borders of the fovea and beyond”

(Wald defines the “photopic zone” as being “dominated by cone vision” and extending to “visual angles of at least 1.5 degrees”. This represents the all-cone fovea where in my explanation cone/cone appositions form the “primary” long wavelength (or “R”) peak and, additionally, precisely define the long wavelength limit (~700 nm) of the visual band.)

The above quote describes the plan of light interaction on the retina as I define. This is undoubtedly the basis for the retinal sensitivity curve that Wald presented in his Nobel lecture (Fig. 15). It is truly beyond me how anyone seeing this, i.e., that color sensitivity is segregated into specific areas or “rings” on the retinal surface did not think to relate this diffractive surface to the wavelength refractive properties of the eye!

From p.1290..My thoughts have been anticipated!

Wald, (after calling it a misconception), quotes:

“Wilmer (1) had thought to explain color vision in terms of only two kinds of cone, or cones, and cone-like rods, the third color mechanism, that for blue, involving the cooperation of ordinary rods Hence, he too expected to find no blue receptors throughout the entire photopic area…”

⁽¹⁾ E.N.Wilmer, Nature 153, 774 (1944), and E.N. Wilmer, J. Theoret. Biol., 1, 141 (1962))

Wald goes on to say that “the photopic area of the retina contains large numbers of such blue-sensitive cones”. This area does contain a (low) density of “blue-sensitive centers”. What I believe that he is actually observing is the statistically small, randomly distributed, density of rod/rod appositions in this critical area (~1.5 degrees) of the retina where rods are just beginning to intrude on a rapidly declining cone density in the retinal morphology.

From p.1294:

“It seems therefore that the absence or near-absence of blue receptor function is characteristic only of the center of the fovea. It is a matter, not primarily of size of field, but of foveal topography”

From p.1296:

“The general gradient of cone concentration in the fovea therefore runs counter to the gradient of blue-cone sensitivity. At the center of the fovea, where cones are most dense, blue-cone sensitivity is minimal, and blue-cones are usually entirely absent. Conversely, at the borders of the photopic area, where the blue-cone sensitivity is highest, the total number of cones has decreased markedly. This opposed distribution is reflected in a converse pattern of relationships that involve the red and green cones”

From p.1298:

“…whereas the sensitivities of the red and green-mechanisms are highest at the center of the fovea, and decline regularly with distance from it, the blue cones show just the opposite gradient of sensitivity, rising from a minimum at the center of the fovea to one half degree to one degree out…”

From p.1299 where Wald recognized the problem of chromatic aberration in the eye:

“Any lens made of one material exhibits chromatic aberration; it refracts short wavelength light more strongly than long wavelength light, and hence brings blue light to a shorter focus than red. Color-corrected lenses can of course be made by using two glasses differing in refractive index; but, so far as is known, no animal has yet succeeded in developing a color-corrected lens. Though the cheapest of cameras have color-corrected lenses, the lens system of the human eye – as Newton observed – has no color correction whatever”

Henceforward , I would propose terming this “chromatic dispersion” instead of considering this effect an aberration

From p.1300:

What we take, therefore, to be normal, trichromic vision is the particular property of an annular zone of the central retina, lying between the blue-blind fixation area and a red-green blind zone some 20-30 degrees out. The special importance of this central zone is that we depend upon it almost exclusively for all phase of photopic vision, and that, all testing of color vision is confined within it, rarely extending more than 2 degrees beyond the fixation point”.

I could not have said it better!

Submitted as revised:

GCH

5/29/08

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