A NEW RETINAL RECEPTOR AT 480 NM ?

by Gerald Huth on March 24, 2011

I have left undefined the nano-antenna response of the retina at eccentricities of ~ 20 degrees. This is the transition region extending from the trichromatic central fovea to ~ 20 degrees devoted to formation of the trichromatic visual image to the solely short wavelength defining, pupil-controlling  wide angle light meter formed by the rod-rod appositions of the peripheral retina.

NOTE: The nano-antenna formed by rod/rod appositions is sensitive to the wavelength that precisely defines the short wavelength limit of the visual band. This limit at ~400 nm abuts the biologically damaging UV region of the electromagnetic spectrum. One once again sees the connection between geometry (essentially determined by the diameter of the rod receptor) and biology.

The following curves (that constitute the fundamental finding of this work) derive from a simple counting of receptor appositions (“nano-antennas”) as a function of retinal eccentricity. The non-intuitive central peak that emerges geometrically defines the exact middle of the visual band (550 nm) and is located at 7-8 degrees where the density of rods is first sufficient to completely surround each remaining cone.. This is the “fulcrum” leading to the synthesis of color that Edwin Land brilliantly deduced must be present somewhere in the vision system. It is a ratio of lightnesses falling on either side of this point that forms color. When the overall intensity of light falling on the image formation area falls below a threshold necessary for the eye to obtain a valid ratio – no color! The remainder of the image – now colorless – remains.

But, what is occurring in this transition region? I have understood that a small residual of cone receptors remains with the general receptor distribution at this point is represented by the drawing in the upper right  (labeled “periphery”) in Plate 6  – again from Pirenne. Note that this   data that has been around for a long time – 1866!

NOTE: I would reiterate that these drawings were made from “fresh – BUT DEAD – retina” and thus will invariably appear distorted. The nano-antenna structure functions in the precise spatial order of the living state.

One might deduce from the figure that cones in this region have a slightly greater diameter that those at smaller eccentricities since something like eleven or more rods are seen surrounding each cone as opposed to the eight at the mid band point (upper left).

This, in turn, would mean, in nano-antenna terms, that the light absorbed at these sites would be of a slightly longer wavelength than exact mid band. In color terms this would mean “slightly towards the red end of the visual band”.

The reason for these sites?

I have come upon the work of S. Berman that is particularly interesting in a number of regards. One paper; A new retinal photoreceptor should affect lighting practice notes  a finding that asserts that a new retinal receptor has been found sensitive at 480 nm. The first paragraph of this paper is worth quoting:

“At the end of year 2002 the prestigious journal ‘Science’ described the discovery of a previously unknown mammalian retinal photoreceptor operating at photopic light levels as among the 10 most important scientific breakthroughs of the year. Evidence for such an additional human photoreceptor came from studies of the spectral response of circadian regulation. 2,3 Further advances in vision science, especially this past year, 4 have provided evidence from studies in humans directly confirming the existence of an additional retinal photoreceptor. While there are some small differences in estimates of the peak wavelength between the circadian studies and the pupillary studies, it is likely that these responses are all manifestations of the same photopigment with a peak sensitivity around 480 nm although after including the spectral transmission of the optic media, the peak sensitivity would shift upward to 491 nm for the human eye.”

The pertinent reference from the above:

Abstract from“Seeing More Clearly: Recent Advances in Understanding Retinal Circuitry”, Shigang He, et al,

“Among 10 breakthroughs that Science announced at the end of 2002 was the discovery of a photosensing (melanopsin-containing) retinal ganglion cell (RGC) and its role in entraining the circadian clock. This breakthrough exemplifies the ultimate goal of neuroscience: to understand the nervous system from molecules to behavior. Light-sensing RGCs constitute one of a dozen discrete RGC populations coding various aspects of visual scenes by virtue of their unique morphology, physiology, and coverage of the retina. Interestingly, the function of the melanopsin-containing RGCs in entraining the circadian clock need not involve much retinal processing, making it the simplest form of processing in the retina. This review focuses on recent advances in our understanding of retinal circuitry, visual processing, and retinal development demonstrated by innovative experimental techniques. It also discusses the advantages of using the retina as a model system to address some of the key questions in neuroscience”.

The concept of “light sensing retinal ganglion cells” is new to me. My consideration is with the physics of light interaction with the outer segments of the cone and rod receptors of the retina.

To be clear,

In the trichromatic nano-antenna construction of the retina proposed in this work, individual sites interact with the wave nature of light in dimensionalities that are within the near field of the light wave (i.e., lateral dimensions of less than a micron) with this space immediately adjacent to a smaller quantum confined electron space that serves as the absorbing mass and provides the electrical input signal for formation of the visual image.

The lateral dimension of the initial light wave-accepting space defines, in antenna terms, the specific wavelength of light absorbed at that site. In the retina only three, geometrically-defined wavelengths  are detected with these corresponding to the long and short ends (700 and 400 nm) of the visual band and, critically, the exact geometrically- determined midband \wavelength (550 nm).

Thus, a transition from the wave nature of light to quantized electron particle occurs at each light detecting site of the retina.

The initial interaction of light with the wave-accepting space occurs in the very fast (femtosecond  or 10-15 sec.) time frame. Absorbed energy is then transferred via a slower phononic/solitonic mechanism through the thylakoid cell membrane to the  adjacent quantum confined electron space. This “thermalizing” mechanism  provides a short term memory function (“memristor”) linking the two spaces that undoubtedly allows time integration of visual image information from the quantum time domain to human nervous system proportions.

Acting as antennas, each light interactive site on the retinal surface possesses  directional properties.  This substantiates the supposition proposed by some that the Fourier transformation  process is involved in the imaging process.

GCH

Ojai, CA

I will leave this here for now, but might the considerations above have been mistaken for a “completely new receptor”?

GCH

Ojai,CA

Edited 3.26.11

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