Biomedical subjects

Mingxia Zhu

Publications and source records attributed to Mingxia Zhu.

3 recordsLinked to original sources

PubMed2006

The contribution of accommodation and the ocular surface to the microfluctuations of wavefront aberrations of the eye.

We have used videokeratoscopy and wavefront sensing to investigate the contribution of the ocular surface and the effect of stimulus vergence on the microfluctuations of the wavefront aberrations of the eye. The fluctuations of the wavefront aberrations were quantified by their variations around the mean and by using power spectrum analysis. Integrated power was determined in two regions: 0.1-0.7 Hz (low frequencies) and 0.8-1.8 Hz (high frequencies). Changes in the ocular surface topography were measured using high-speed videokeratoscopy and variations in the ocular wavefront aberrations were measured with a wavefront sensor. The microfluctuations of wavefront aberrations of the ocular surface were found to be considerably smaller than the microfluctuations of the wavefront aberrations of the total eye. The fluctuations in defocus while viewing a closer target at 2 or 4 D were found to be significantly greater than fluctuations in defocus when viewing a far target. This increase in defocus fluctuations (p < or = 0.001) occurred in both the low- and high-frequency regions of the power spectra.

Accommodation, Ocular↗

PubMed2004

Analyzing the dynamic wavefront aberrations in the human eye.

The optics of the human eye are not static in steady viewing conditions and exhibit microfluctuations. Previous methods used for analyzing dynamic changes in the eye's optics include simple Fourier-transform-based methods, which have been used in studies of the eye's accommodation response. However, dedicated tools for the analysis of dynamic wavefront aberrations have not been reported. We propose a set of signal processing tools, the combination of which uncovers aspects of the dynamics of eye's optical aberrations which were hidden from conventional analysis techniques. The methodology includes extraction of artifacts from potentially significant eye movements, filtering, optimal parametric signal modeling, and frequency and time-frequency representations. The exposition of the techniques and their advantages over traditional techniques is illustrated for real dynamic eye wavefront aberration measurements.

Algorithms↗

PubMed2004

Microfluctuations of wavefront aberrations of the eye.

To investigate fluctuations in the wavefront aberrations of the eye and their relation to pulse and respiration frequencies we used a wavefront sensor to measure the dynamics of the Zernike aberrations up to the polynomial fourth radial order. Simultaneously, the subject's pulse rate was measured, from which the instantaneous heart rate was derived. We used an auto-regressive process to derive the power spectra of the Zernike aberration signals, as well as pulse and instantaneous heart rate signals. Linear regression analysis was performed between the frequency components of Zernike aberrations and the pulse and instantaneous heart rate frequencies. Cross-spectrum density and coherence analyses were also applied to investigate the relation between fluctuations of wavefront aberrations, and pulse and instantaneous heart rate. The correlations between fluctuations of individual Zernike aberrations were also determined. A frequency component of all Zernike aberrations up to the fourth radial order was found to be significantly correlated with the pulse frequency (all R(2) >/= 0.51, p < 0.02), and a frequency component of nine out of 12 Zernike aberrations was also significantly correlated with instantaneous heart rate frequency (all R(2) >/= 0.46, p < 0.05). The major correlations among Zernike aberrations occurred between second-order and fourth-order aberrations with the same angular frequencies. Higher order aberrations appear to be related to the cardiopulmonary system in a similar way to that reported for the accommodation signal and pupil fluctuations.

Accommodation, Ocular↗