Static accommodation and the minimum angle of resolution.

Some simple assumptions lead to the prediction that, under a wide range of practical circumstances, the magnitude of the slope, m, of the linear portion of the static, monocular, accommodation response/stimulus curve is linearly related to the minimum angle of resolution (MAR) achievable by the observer under the conditions of observation in use. This linear relation, of the form [m] = 1-C(MAR) where C is a constant, would be expected to apply up to the value of MAR at which the slope falls to zero; higher values of MAR would always yield zero slope. Using data from the existing literature, it is shown that the prediction is approximately fulfilled when MAR is varied by blurring the target, by reducing target luminance, by changing target contrast, by altering the retinal location on which the target image falls, or by observer amblyopia. However, the derived value of MAR at which the slope falls to zero is found to vary between about 2 and 40 min arc (i.e., C lies between 0.025 and 0.5 min-1), depending upon the origin of the variation in MAR. Some possible reasons for this variation are discussed.