Wave aberrations were measured with a Shack-Hartmann wavefront sensor (SHWS) in the right eye of a large young adult population when accommodative demands of 0, 3, and 6 D were presented to the tested eye through a Badal system. Three SHWS images were recorded at each accommodative demand and wave aberrations were computed over a 5-mm pupil (through 6^{th} order Zernike polynomials). The accommodative response was calculated from the Zernike defocus over the central 3-mm diameter zone. Among all individual Zernike terms, spherical aberration showed the greatest change with accommodation. The change of spherical aberration was always negative, and was proportional to the change in accommodative response. Coma and astigmatism also changed with accommodation, but the direction of the change was variable. Despite the large inter-subject variability, the population average of the root mean square for all aberrations (excluding defocus) remained constant for accommodative levels up to 3.0 D. Even though aberrations change with accommodation, the magnitude of the aberration change remains less than the magnitude of the uncorrected aberrations, even at high accommodative levels. Therefore, a typical eye will benefit over the entire accommodative range (0–6 D) if aberrations are corrected for distance viewing.

*SD*for any of the accommodative stimuli). For static population statistics, two additional eyes that had undergone LASIK refractive surgery were also excluded. Therefore, a total of 76 subjects are reported for the changes in aberration with accommodation, and 74 subjects for the population statistics. All subjects had good ocular health with best-corrected visual acuity better than 20/30 (average 20/17) in the tested eye. The subjects ranged in age from 21–40 years with a mean (+/−

*SD*) of 24.8 +/− 4.0 years. The spherical refractive error ranged from + 1.25 D to −8.25 D with a mean (+/−

*SD*) of −2.50+/−2.25 D; and the astigmatism ranged from −0.25 D to −2.75 D with a mean (+/−

*SD*) of −0.70+/−0.54 D. Significant refractive errors were corrected with spectacles or trial lenses during the experiment. The mean (+/−

*SD*) residual uncorrected refractive error was −0.43+/−0.60 D for the sphere and −0.17+/−0.31 D for the cylinder.

*W*(

*x,y*), is represented by a weighted sum of the series of Zernike modes:

*W*(

*x,y*) is defined over the

*x,y*coordinates of the pupil,

*C*is the Zernike coefficient corresponding to a particular Zernike mode,

*Z*, and

*n*and

*m*refer to the different radial and angular orders, respectively. Zernike coefficients representing the wave aberration were specified using the standard nomenclature defined with reference to the standard coordinate system recommended by the Optical Society of America (Thibos, Applegate, Schwiegerling, Webb, & VSIA Standards Taskforce Members, 2000).

^{th}order Zernike polynomials. For every subject, three sets of SHWS images were analyzed for each accommodative stimulus. The subject's wave aberration under a particular stimulus condition was represented by the mean Zernike coefficient of three measurements.

^{rd}and 4

^{th}order aberrations, the 5

^{th}and 6

^{th}order wavefront errors contribute much less to the total variance of the wave aberration.

^{nd}through 6

^{th}order, excluding defocus) as a function of the change in accommodative response for individual subjects. Among all the aberrations, spherical aberration (Z12) shows the largest change with accommodation. The change in spherical aberration is always negative, indicating that spherical aberration always moves in a negative direction with increased accommodation. The amount of change in spherical aberration is linearly related to the amplitude of accommodation (slope = − 0.0435 micrometers/D,

*r*= 0.85, 95% confidence predictive range at any level of accommodation is +/− 0.085 micrometer). Coma (Z7, Z8) and astigmatism (Z3, Z5) also change with accommodation, but the direction of the change varies, going in either a positive or negative direction. The change in other terms is much smaller and reveals no clear trend. Figure 4 plots the RMS of the change in the astigmatism terms (Z3 and Z5 combined), the coma terms (Z7 and Z8 combined), and spherical aberration term (Z12) with accommodation. The rates of change of coma and astigmatism are about one third that of spherical aberration for a 5-mm pupil size. Special considerations taken while computing the RMS of the difference between two measured variables are described in the Appendix.

*SD*for all subjects for the 0 D stimulus was +/− 0.135 D for defocus, indicating a stable accommodative state. In young human eyes, it is known that the positive corneal spherical aberration is partially balanced by the negative spherical aberration of the internal optics, mainly the crystalline lens (Artal, Guirao, Berrio, & Williams, 2001; El Hage & Berny, 1973; He, Gwiazda, Thorn, & Held, 2003a; Smith, Cox, Calver, & Garner, 2001). The positive spherical aberration we observed for the whole eye thus represents the residual positive spherical aberration from the anterior corneal surface.

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*change*of aberrations will be elevated because each value is sitting on a noise floor caused by uncertainty in the measurements. The size of the noise floor depends on the noise in each measurement and is specific to each device and method of data collection.

*SD*, term by term, for all of the subjects in the study. The

*SD*for each subject was based on three measurements, which itself is not a sufficient number of samples to determine the error, but the average of many subjects is. Once the average

*SD*for each term was known, we computed the SEM for each term \(({\rm SEM} = SD/\sqrt{3})\), considering three measurements. The SE of the difference between two repetitive measurements for each term was calculated as \(\sqrt{2}.{\rm SEM}\). The noise floor was calculated as the RMS of the SE of the difference for all the terms. For the plots on Figure 4, the noise floor for astigmatism (Z3 and Z5 combined), coma (Z7 and Z8 combined), and spherical aberration (Z12) were 0.044, 0.033, and 0.013 micrometers, respectively. For the total 2

^{nd}to 6

^{th}order RMS values (excluding defocus), the noise floor was 0.075 micrometers. These amounts were subtracted from each difference value in the scatter plots of Figure 4 and the bar graphs of Figure 6. Not subtracting the noise floor values gives rise to erroneous overestimations of the RMS of the change in aberrations. Incidentally, computing the noise floor also provides a value that indicates the repeatability of the wavefront measurement.