Short-term adaptive modification of dynamic ocular accommodation.

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Short-term adaptive modification of dynamic ocular accommodation. Invest Ophthalmol Vis Sci. 2009 Feb 28; Authors: Bharadwaj SR, Vedamurthy I, Schor CM Purpose: Indirect observations suggest that the neural control of accommodation might undergo adaptive recalibration in response to age-related biomechanical changes in the accommodative system. There has however been no direct demonstration of such an adaptive capability. This investigation aims to demonstrate short-term adaptation of accommodative step response dynamics to optically induced changes in neuro-muscular demands. Methods: Repetitive changes in accommodative effort were induced in 15 subjects (18 to 34 years) using a double-step adaptation paradigm wherein an initial 2D step change in blur was followed 350ms later by either a 2D step increase in blur (increasing-step paradigm) or a 1.75D step decrease in blur (decreasing-step paradigm). Peak velocity, peak acceleration and latency of 2D single step test responses were assessed before and after 1.5 hours of training with these paradigms. Results: Peak velocity and peak acceleration of 2D step responses increased following adaptation to the increasing-step paradigm (9 of 12 subjects) and they decreased following adaptation to the decreasing-step paradigm (4 of 9 subjects). Adaptive changes in peak velocity and peak acceleration generalized to responses that were smaller (1D) and larger (3D) than the 2D adaptation stimulus. The magnitude of adaptation was poorly correlated with the subjects age but it was significantly negatively correlated with the pre-adaptation dynamics. Response latency decreased following adaptation, irrespective of the direction of adaptation. Conclusions: Short-term adaptive changes in accommodative step response dynamics could be induced, at least in some of our subjects between 18 and 34 years, with a directional bias towards increasing compared to decreasing the dynamics. PMID: 19255153 [PubMed - as supplied by publisher]

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