Temporal dynamics and statistical characteristics of the microfluctuations of accommodation: dependence on the mean accommodative effort.

Microfluctuations of accommodation have been the subject of many studies. New technological developments now permit us to study the dynamics of the microfluctuations with unprecedented resolution and accuracy. We aim to characterise their temporal statistics for different levels of accommodative effort, using a custom-built aberrometer. We conducted 46 s long measurements on the dominant eye of 9 young, healthy subjects. The ocular wavefront was sampled every 250 microm across the 3.9 mm measured pupil, at a frame rate of 173 Hz. This enabled us to obtain high resolution estimates of the Power Spectral Density (PSD). Results show that the shape of the estimated PSD for a 4 D effort is distinct from the shape for the two extrema of the accommodation range. The autocorrelation function of the increments of the accommodation signal is also affected by the level of effort, regardless of the refractive error of the subject.

New methodology to measure the dynamics of ocular wave front aberrations during small amplitude changes of accommodation.

We present a methodology to measure the systematic changes of aberrations induced by small changes in amplitude of accommodation. We use a method similar the one used in electrophysiology, where a periodic stimulus is presented to the eye and many periods (epochs) of the stimulus are averaged. Using this technique we have measured changes in higher order aberrations from 0.006 mum to 0.02 mum and correlated them with amplitude changes of accommodation as small as 0.14D. These small changes would have been undetectable without epoch averaging. The correlation coefficients of Zernike terms with defocus were calculated, demonstrating higher values of correlation for epoch averaging. The accurate monitoring of defocus at the start of the accommodation response has shown some interesting trends that may be related with the mechanisms behind accommodation.

Effects of retinal scattering in the ocular double-pass process.

The validity of double-pass wave-front measurements in the eye is reviewed analytically and computationally. A mathematical description of the scalar optical field in the exit pupil plane after an ocular double-pass process is presented. With the help of this description, the relationship between the phase information losses and the statistical properties of retinal scattering is demonstrated.