Indian Journal of Science and Technology
Year: 2017, Volume: 10, Issue: 25, Pages: 1-5
Nachieketa K. Sharma*
*Author for correspondence
Nachieketa K. Sharma
Department of Physics, Institute of Technical Education & Research, Siksha ‘O’ Anusandhan University, Khandagiri Square, Bhubaneswar – 751030 Orissa, India; [email protected]
The objective of this work is to show how the retina responds to the loss of luminance efficiency due to increasing departure from either unit contrast or unit spot-size ratio in a compensative fashion. The methods adopted are two-wave interference and the single mode wave guiding of a photoreceptor cone. A correlation is established between loss of luminance efficiency due to oblique incidence and contrast in the interference pattern. Similarly, a relation between the fraction of the power that is not able to be coupled to a cone due to the peripheral entry of light and the spot-size ratio departure is developed. The findings are that due to maximum departure from unit contrast, the retinal response takes the traditional StilesCrawford route, but with no departure the Stiles-Crawford Effect of the first kind (SCE I) becomes totally irrelevant for the retina and for intermediate situations (between unit and zero contrast) the retinal response is controlled by a modified SCE I weakened proportionate to the contrast of the interference pattern on the retina. Likewise, when the incident spotsize and the waveguide mode spot-size match, the spotsize ratio is unity, departure is zero, the coupling of power is 100% and visibility loss is zero. But with gradual enhancement in the spot-size ratio departure, the visibility loss also increases. Again, a visibility loss of 90 % corresponds to a departure of either 6-fold or 1/6-fold (equivalent to a pupil entry point of 4 mm). This suggests that a pupil entry point of 3.5 mm may point to a loss of 70-80 %, a result reached with departure from contrast also. This way of correlating the retinal response to either contrast or spot-size ratio has the advantage of employing them as potential biomarkers for early detection of diseases affecting the photoreceptors.
Keywords: Biomarker, Contrast, Retinal Response, Spot-size Ratio, Stiles-Crawford Effect, Visibility Loss
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