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Benjamin Lochocki, Carmen Vela-Garcia, Brian Vohnsen; Frequency Analysis of the Transient Stiles-Crawford Effect. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4825.
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The retina and photoreceptors are the last optical elements of the eye that interact with light prior to absorption and triggering of neural responses. Thus, the retina plays a key role for vision on par with the cornea and crystalline lens, and further understanding is needed for improved eye modelling and to enrich the understanding of the visual process. The aim of this study is to examine temporal responses of the classical Stiles-Crawford effect with Maxwellian view as commonly related to waveguiding by individual photoreceptor cones.
The transient Stiles-Crawford Effect (T-SCE) reflects a visual impact of sudden changes to illumination conditions when determining directionality of the cones in the pupil plane. Here, it is examined for the fovea region of the authors’ eyes using tuneable crystal filters for wavelength, bandwidth and brightness control in conjunction with a fast galvanometric scanning mirror. Across-the-pupil scans centred at the point of best visibility have been realized varying the frequency and duty cycle for an offset temporal and nasal Maxwellian source. The semi-automated system includes correction for defocus and blanks out extraneous sources of variability in the determination of photoreceptor directionality.
The experimental results show a subtle impact of frequency on the directionality of the T-SCE for all subjects that may relate to the finite response time of the visual pigments. Changing the angle of incidence may impact on the photoreceptor light guiding allowing the light to reach other photoreceptor pigments. The obtained results are analyzed and compared favourable to the waveguide model of individual photoreceptor cones.
The implemented methodology has allowed us to explore photoreceptor directionality and the temporal responses of cone photopigments in a novel way. It may have potential to explore photoreceptor alignment mechanisms and improve our understanding of the coupling between incident light and vision. This is also essential for improved refractive optical design, intraocular lenses, and the understanding of the optical impact of photoreceptor degeneration.
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