It is well known that the eye's optics exhibit temporal instability in the
form of microfluctuations in focus; however, almost nothing is known of the
temporal properties of the eye's other aberrations. We constructed a real-
time Hartmann-Shack (HS) wave-front sensor to measure these dynamics at fre
quencies as high as 60 Hz. To reduce spatial inhomogeneities in the short-e
xposure HS images, we used a low-coherence source and a scanning system. HS
images were collected on three normal subjects with natural and paralyzed
accommodation. Average temporal power spectra were computed for the wave-fr
ont rms, the Seidel aberrations, and each of 32 Zernike coefficients. The r
esults indicate the presence of fluctuations in all of the eye's aberration
, not just defocus. Fluctuations in higher-order aberrations share similar
spectra and bandwidths both within and between subjects, dropping. at a rat
e of approximately 4 dB per octave in temporal frequency. The spectrum shap
e for higher-order aberrations is generally different from that for microfl
uctuations of accommodation. The origin of these measured fluctuations is n
ot known, and both corneal/lenticular and retinal causes are considered. Un
der the assumption that they are purely corneal or lenticular, calculations
suggest that a perfect adaptive optics system with a closed-loop bandwidth
of 1-2 Hz could correct these aberrations well enough to achieve diffracti
on-limited imaging over a dilated pupil. (C) 2001 Optical Society of Americ
a.