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C. Leahy, C. Leroux, C. Dainty, L. Diaz-Santana; Temporal Dynamics and Statistical Characteristics of the Microfluctuations of Ocular Wavefront Aberrations. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1562.
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© ARVO (1962-2015); The Authors (2016-present)
Microfluctuations of accommodation have been the subject of many studies. Few of them have looked at the effect that they have on the overall wavefront aberrations, or at the statistical description of their dynamics. New technology developments permit now to address these issues with unprecedented resolution and accuracy. We aim at studying the dynamics of the wavefront aberrations introduced by microfluctuations of accommodation and characterising their temporal statistics at different target distances during steady state accommodation.
A custom-built aberrometer was implemented (5.4mm diameter pupil, 250µm spatial sampling and 150Hz frame rate). We conducted measurements on the right eye of 5 healthy subjects (25 to 40 years old). For each subject we collected 9 trials at each of 3 fixation target distances (far point, near point, and mid-point between them). Each trial was 26 seconds in duration (4,000 data points per trial, 36,000 data points in total). The time series of the wavefront RMS and its derivative were calculated for each trial (RMS was estimated from a 5th order Zernike polynomial expansion). Probability density functions (PDF) for the time series and their derivatives were found.
The PDFs of the time series were found to be non-Gaussian, exhibiting heavy tails and skewness. We found that the degree of the heavy-tailed effect is dependent on the level of accommodation, in that the heavy tails are more apparent at fixation distances corresponding to the near point and mid-point than at the far point. In many cases the derivative of the RMS under accommodation exhibits a Lévy-type stable PDF.
We have shown that the dynamics of aberrations show non-Gaussian statistics and that they present heavy-tailed and in some cases, skewed PDFs. We noted that the heavy tails were more apparent during active accommodation. This leads us to suggest that the observed PDFs of the RMS wavefront resulting from microfluctuations of accommodation may be the result of the coupling between the RMS wavefront aberration and the accommodative control system. Lévy-like statistics are often related with optimal control strategies [Cabrera and Milton (2004), Eurich and Pawelzik (2005)], hence we propose for future work to investigate this matter further.
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