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A. Glasser, V. Sethi, C. Shooner, M. Wendt, M. Franchek; Biomechanical Analytical Analysis of Dynamic Accommodation in Rhesus Monkeys . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5848.
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© ARVO (1962-2015); The Authors (2016-present)
Accommodation is a dynamic process that is subject to anatomical biomechanical constraints. Aging may influence biomechanical structures and thereby alter accommodative dynamics as well as decreasing accommodative amplitude. Accommodation models have been developed based on step responses. Dynamic analysis based on frequency response information of physiological accommodation will also facilitate the development of analytical models to understand the biomechanics of accommodation and the effects of age
Accommodation was stimulated via the Edinger–Westphal nucleus in rhesus monkeys with a carrier frequency of 100Hz for 20 minutes. Accommodative responses were recorded at 100Hz as dynamic change in lens thickness with continuous ultrasound biometry. Several stimulus input signals were constructed in MATLAB and delivered via a personal computer and a dSPACE A/D real time data acquisition system. Stimulus signals included the evaluation signal of white noise up to 48 Hz, and a swept sine signal from 0.1 – 10 Hz. Using the input signal of white noise and output signal of lens thickness, a non–parametric frequency response was evaluated. This non–parametric model provides information regarding the structure of the model of the eye which includes the order of the model and its break frequencies. From the captured information of input/output dynamics a parametric truncated Volterra series model was identified.
Accommodative responses were sustained throughout the 20 minute stimulus durations. The frequency response model identified from the truncated Volterra series contains linear, quadratic and cubic terms with break frequencies of 0.45 Hz, 1.5 Hz and 3 Hz respectively. The quadratic and cubic terms essentially captured the asymmetric accommodative and disaccommodative responses. The truncated Volterra series of low order provides a good characterization of the eye. Experimental validation of the frequency domain model was carried out in the time domain using the swept sine data. The variation between the model and the norm was 6% for a period of 100 seconds with a mean square error of 1.5%. Good corroboration between the experimental data and model results was achieved.
Edinger–Westphal stimulated accommodation in rhesus monkeys with dynamic analysis can be used to develop biomechanical analytical models to study the accommodative process with the goal of understanding the influence of biomechanical age changes on the dynamics of accommodation.
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