SENSITIVITY ANALYSIS OF THE STIMULUS-RESPONSE FUNCTION OF A STATIC NONLINEAR ACCOMMODATION MODEL

The effect of parameter variation of a nonlinear static feedback contr ol model of the accommodation-system was investigated. Simulations of a MATLAB/SIMULINK model showed a nonlinear relationship between stimul us and response in which the response curve was above the 1:1 line in the region to the left of the crossover and below the 1:1 line in the region to the right of the crossover. At the crossover, the response c urve exhibited an inflection that was constant and equal to the tonic accommodation value (ABIAS), Sensitivity analysis showed that increasi ng depth of focus (deadspace range between +/-DSP) increased the separ ation between the boundary lines of the deadspace region, with a large r separation associated with late-onset myopia and congenital nystagmu s. Increasing accommodative controller gain (ACG) increased the slope of the function on either side of the deadspace, with lower ACG values corresponding to lower slopes that indicated an amblyopic deficit. In creasing ABIAS increased the accommodative level at the inflection reg ion, In addition, the saturation level of the accommodative response d ecreased with increasing age, while the slope remained the same, which was consistent with the Hess-Gullstrand theory of presbyopia. The acc uracy and relative simplicity of the model indicated that it could ser ve as a basis for further comprehensive investigation of the basic and clinical aspects of the accommodation system.