THE SPATIAL AND TIME DOMAINS OF LIGHT INTERACTION WITH THE RETINA
March 27th, 2009 | No Comments »
HBB/FL
I have previously published a diagram (“Diagram of the Basic Light Absorption Process in the Retina”, Jan. 10, 2008) showing what I believed to be the mechanism involved in the interaction of light with the outer segments of retinal receptors. In contrast with traditional views, I have proposed that light is absorbed as the electromagnetic wave in the spaces (exactly three are geometrically defined) between adjacent quantum confined electron sites contained within each receptor. I have described this interaction as occurring “between adjacent receptors” that is contrasted with the historically held view (in every textbook on vision!) that “photons interact with pigments contained within receptors”. But I really must be more precise refining both the space and time aspects of that statement.
The following is the initial diagram:
In summary, the diagram attempts to portray light interaction in three distinct regions:
I Initially, light is absorbed in the spaces between adjacent receptor outer segments (to the left in the diagram) fundamentally interacting as the electromagnetic wave of classical physics.
II A transition region where the absorbed energy is thermalized (i.e., “slowed in time”) via phononic mass transport along the membrane of the thylakoid disks that form the body of the receptor segments. Intercalation of cholesterol into this lipid membrane indicates that a lossless soltonic mechanism may actually be operative.
III With the absorbed energy finally arriving at the central array of rhodopsin complexes that form the quantum confined electron (QCE) sites within the receptor and effecting the signal-producing isomerization of the retinal molecule. This final process generates the quantized electron particle that is used in synthesis of the visual image.
The diagram shows only half of the process, i.e., interaction with only one receptor. Two adjacent receptors will actually be involved in the detection process forming a “near field optical antenna” structure between them.
It is apparent, therefore, that the array of retinal outer segments is a biologically evolved nanostructure that functions at each light interaction center to translate light as an electromagnetic wave into quantum-confined electron particles.
(I will leave for the time being discussion of the fundamental implications of this finding to physics).
Many new considerations follow from the above.
The function of the opsin moiety of the rhodopsin complex is seen to be actually spatial whose function is to spatially define and orient these complexes to conform to a specific configuration –either what have traditionally been termed the “rod” or “cone” structures. Rhodopsin is seen to be not an “optical pigment accepting the interaction of photons” but is rather a space-filling entity that has a secondary role of orienting the retinal signal processing molecule so that it conforms to a proper dichroic orientation for accepting energy in consonance with the mechanism absorbing light.
This orientation is consistent with the long known, but never explained, measurements indicating that the rhodopsin complexes within receptors are dicroically oriented to accept light absorption orthogonal to the direction of incident light. This was always inconsistent with the idea that “photons interact” in the axial direction and led to such ridiculous notions as the “photon catch” hypothesis!
This orthogonal-to-the-direction-of-light–incidence energy transduction mechanism is repeated in each of the thousands of stacked thylakoid disks that form the axial length of each receptor outer segment. This allows one to conceptualize the formation of a differential electronic signal (a “giant dipole”) generated from individual interactions at each of the thousands of points along the length of each outer segment. I propose that such a differential signal encodes the direction of the incident light providing the second parameter of the Fourier equation showing, in turn, that the plane of light interaction with the retina is actually the Fourier plane of the optics of the eye. The fundamental mechanism of vision thus involves detection and solution of a two dimensional Fourier transform!
To summarize – all of the above occurs spatially within the near field of the wavelength of visible light. The lateral dimension of the individual light detection centers is consistent with this being less than one micron (10-6 m) with the central QCE centers occupying even less space – of nanometer
(10-9 m) dimension. Such structures are electronically consistent with operation in the very fast – femtosecond (10-15 sec) - time domain. This, in turn, agrees with reported, and again not explained, measurements showing that the signal-producing isomerization of the retinal molecule occurs in this time frame.
Events at the light interacting retinal outer segments therefore involve the wave/ particle duality of quantum physics. The retina functions to interact in very fast femtosecond time and to slow the “interaction signal” to human nervous system compatible proportions.
The vision process was never the “millisecond camera” that has been for so long assumed and taught.
Further progress in understanding the vision process will involve quantum processes such as the femtosecond spectroscopy discovery of a “quantum coherence” effect in the photosynthetic apparatus.
ADDITIONALLY:
Now one must consider (and ultimately explain) that each individual thylakoid disk, the stacking of which forms the body of each receptor segment, contains not one but thousands of rhodopsin monomers intercalated into the membrane disk-forming structure. See, for example, Fotiadis et al, (NATURE | VOL 421 | 9 JANUARY 2003) with a quote from their paper:
“In vertebrate retinal photoreceptors, the rod outer-segment disc membranes contain densely packed rhodopsin molecules…….” (Fotiadis et al, Nature, Vol.421 | 9 January 2003). Further from the same reference: “it is….revealed rows of rhodopsin pairs densely packed in paracrystalline arrays. Packing densities were 30,000–55,000 rhodopsin monomers per mm2, with an average density of 48,300 to 58,300 monomers per mm2.
This work uses infrared-laser atomic-force (AFM) microscopy to reveal that the arrangement of rhodopsin complexes within the membrane of the disks form spatially ordered paracrystalline arrays of dimers. It is instructive to view their figures (specifically their Fig. 2) illustrating the exquisite spatial order of these molecules.
Following the logic of this work this ordered structure would seem to support the idea of an additional directional function, i.e., a second energy- accepting directionality beyond the dichroic orientation of single retinal molecules discussed above. This additional directionality would lie in the plane of the membrane and be oriented toward adjacent receptors. One then visualizes three dimensional – and directional – energy acceptance!
GCH
3.27.09
Ojai,CA
