The Quantum Limit of the Vision Process
September 5th, 2007 | No Comments »It has long been documented that the process of vision has evolved to the quantum limit, i.e., that the eye can detect and process the interaction of single photons. The mechanism underlying this extraordinary ability has never having been explained. I believe that an explanation follows from a consideration of the extraordinary density of light interaction sites on the retinal surface. This number approximates one hundred million per square centimeter. Then must introduce the magnitude of the light fluence - the number of individual photons per unit area - incident on the retina. This fluence is dynamically controlled for varying lighting conditions by the constriction and dilation of the pupil of the eye. Movement of the pupillary musculature to effect this control is, in turn, controlled by the short (blue) wavelengths of visual response interacting with the “wide angle light meter” formed by the detection centers of the peripheral retina (that are, in electrical engineering terms, “ganged together” or connected in parallel). Thus the density of photons allowed to enter the eye and fall on the retina is under continuous control and, I might guess, maintained within a narrow range. Using a number for photon fluence that corresponds to normal daylight conditions together with the number density of retinal light detection centers, a simple calculation shows that the probability of two photons being simultaneously incident on any one of the hundred million or so of light detection centers is approximately 10-7 – or negligible. Thus the possibility of two-photon, out of phase signal cancellation is nil providing an explanation for the high quantum efficiency of the retinal surface. This conclusion in-turn implies that retinal light detection centers act individually in detecting single photons –an observation supported by the above noted, and accepted, finding that the eye can detect single photons. Q.E.D.
Each individual light detection center of the retina that, according to this work, comprises an inter-receptor space adjacent to the electron quantum confinement site* provided by the retinal/rhodopsin complex within the mass of a receptor, is capable of wavelength-selective detection and generation of an electronic signal useful by the human nervous system….with this composite device being sensitive to the interaction of a single photon. Moreover, it is clear the this process must occur in a heretofore unconsidered time domain approximating 10-15 seconds (or femtoseconds). The vision process considered at the retina implies the involvement of the discipline of quantum physics.
*The length of a retinal receptor (cone or rod) contains many individual retinal/rhodopsin sites forming a “quantum wire” the definition of which is a region where the electron is quantized and free to move in only one direction, i.e., along the length of the receptor or “wire” to underlying retinal circuitry. It is probable therefore that even this electrical signal is quantized.
A NOTE:
I have noted previously that the reason for my use of the term “photon” is that it is commonly accepted and understood. In the spirit of this work I would rather substitute “quantized interaction” to reflect what I have found to be the “wave/particle” nature of light interaction with the retina.
GCH
9/05/07
