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Michele Rucci, Jonathan Victor; Temporal Cues to Defocus in Emmetropia and Myopia. Journal of Vision 2018;18(10):628. doi: https://doi.org/10.1167/18.10.628.
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During development, the eye tunes its size to its optics so that distant objects are in focus, a state known as emmetropia. The visual signals entering the eye are generally considered to play an important role in this process, but the relevant features of the retinal image (e.g., blur magnitude) are unclear, as are the mechanisms by which these features are extracted. Here, recognizing that the retinal input is not merely an image but a spatiotemporal flow of luminance, we propose that temporal features generated by fixational eye movements (FEMs) are critical. FEMs occur incessantly in humans and other mammals, transforming the spatial scene into temporal modulations on the retina, thus acting as a key step for encoding fine-scale spatial information (review: Rucci & Poletti, Annual Reviews of Vision Sciences 2015). Specifically, (a) FEMs enhance─rather than degrade─high spatial frequency vision during natural post-saccadic fixation, an effect that appears to originate both from precisely-directed microsaccades and the temporal modulations given by ocular drift, and depends on the temporal resolution of retinal circuitry; (b) the luminance modulations resulting from FEMs counterbalance the spatial frequency distribution of the natural world, yielding a spatiotemporal input to the retina with equal temporal power across spatial frequencies; and (c) FEMs, both microsaccades and drift, are under a surprising degree of oculomotor control. Building upon these recent results, we propose that the space-time reformatting caused by FEMs also plays a role in emmetropization. The fixational redistribution of power on the retina suggests several ways in which FEMs could provide blur information, all grounded in the spatiotemporal remapping that they induce. We describe some of these possibilities and their implications for emmetropization. A direct consequence of our viewpoint is that abnormal oculomotor behavior may contribute to the development of myopia and hyperopia.
Meeting abstract presented at VSS 2018
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