Pupil scaling for the estimation of aberrations in natural pupils.

PURPOSE: This study aimed to validate the mathematical Zernike pupil size scaling from bigger pupils to smaller pupils, and vice versa, by comparing the estimates of the Zernike coefficients with corresponding clinical measurements obtained at different pupil sizes. METHODS: The i.Profiler Plus (Carl Zeiss Vision, Inc, USA) was used to obtain measures of wavefront aberrations for two pupil sizes (3 mm and the maximum natural pupil size) from the right eyes of 28 visually normal subjects (mean [±SD] age, 57 [±7] years) whose maximum pupil size was greater than or equal to 5 mm without pharmacological dilation. Zernike coefficients were estimated for a 3-mm pupil size scaling down from the measured data of the maximum natural pupil size and, similarly, for the maximum pupil size scaling up from the measured data of the 3-mm pupil. RESULTS: The differences between the estimated and measured values were not significantly different (repeated-measures analysis of variance; p > 0.05) over the range of pupil sizes examined, irrespective of whether the estimates were made by scaling up from a small pupil or scaling down from a large pupil. However, the difference between the measured and estimated coefficients was more variable and less systematic when scaling to a larger pupil size when compared with scaling to a smaller pupil size. CONCLUSIONS: Estimation of ocular wavefront aberration coefficients either scaling down from large to smaller pupils or scaling up from smaller to large pupils provides estimates that are not significantly different from clinically measured values. However, when scaling up to a larger pupil size, the estimates are more variable. These findings have implications for pupil scaling on an individual basis, such as in cases of refractive surgery or when using pupil scaling to examine a clinical cohort.

Centroid displacement statistics of the eye aberration.

We discuss a method for the study of the spatial statistics of the ocular aberrations, based on the direct use of the Hartmann-Shack centroid displacements, avoiding the wavefront reconstruction step. Centroid diagrams are introduced as a helpful aid to visualize basic properties of the aberration datasets, and slope-related second-order statistical functions are applied to check the compatibility between the experimental data and different models for the aberration statistics. Preliminary results suggest that no single power-law spectrum (e.g., Kolmogorov's) is able to represent the whole range of spatial statistics of individual eye fluctuations and that more elaborated models, including at least the contribution of a relevant defocus fluctuation term, are required. This centroid-based approach allows for an easier intercomparison of results between laboratories and avoids the bias and information loss associated with the estimation of a reduced number of Zernike coefficients from a much wider slope data set.