Sensory-Motor Control of the Binocular Near Response is a basic study of the progressive reduction of accommodative amplitude that occurs with age (presbyopia) and how it influences the coordination of focusing responses and binocular eye alignment (the near response). Incipient presbyopia begins in childhood and progresses as the amplitude of accommodation declines linearly with age until the end of the fourth decade of life when virtually all eyes become unable to accommodate by changing optical power of the eyes. While research during the past century has concentrated on the biomechanical properties of the structural components of accommodation and on the age-related biomechanical changes in these structures that lead to presbyopia, advances in knowledge of how neural control of accommodation adjusts to these changes has been very limited. This proposal investigates the optimization of the near response by adapting neural control of accommodation and convergence in response to age-related biomechanical changes of the accommodation plant that underlie the natural progression of presbyopia. The proposal addresses (1) the ability to adapt accommodation to preserve youthful accommodative dynamics in response to age-related changes in visco-elastic properties of the crystalline lens, (2) the influence of adapting dynamic accommodation and convergence on their dynamic cross-coupled interactions, (3) adaptation of the static cross-coupled interactions between accommodation and convergence in response to age-related biomechanical changes of the ocular lens, (4) calibration of consensual accommodation to potential unequal aging of the two ocular lenses, and (5) decline of adaptation ability with age. Results will be interpreted with models of the dynamic properties of accommodation and their interactions with convergence, in order to understand how adaptation could extend the linear operating range of the near response with age. Results of these experiments will provide fundamental knowledge about the adaptive mechanisms that compensate for the decline of accommodation with age, and interactions between accommodation and convergence that influence the accuracy of binocular eye alignment. In addition, models developed from the experiments can facilitate the successful design and implementation of new treatments, such as accommodating intra-ocular lenses, designed to offset presbyopia.
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