Abstract
Abstract: :
Purpose: It is relatively well known that the higher–order aberrations of the eye fluctuate over short time periods. Currently however, the origin of these fluctuations has not been determined with certainty. In the literature there are many events correlated with the pulse, such as corneal pulsation and the high frequency component of the microfluctuations in accommodation. The aim of this investigation was to determine if these associated changes in the eye due to the pulse are responsible for the dynamic characteristics of the higher–order aberrations. Methods: Five subjects were used. The aberrations were measured with a Shack–Hartmann sensor operating at 21.2 Hz. A novel feature of the system is the closed–loop correction of astigmatism via a rotating cylinders and Badal optometer arrangement. The pulse pressure wave was simultaneously measured using photoplethysmography, and from this the heart rate variability was also derived. Further experiments were carried out on two subjects in which the properties of the pulse and heart rate variability were changed to see if corresponding changes could be observed in the rms wavefront error. One example included a comparison between a subject holding their breath and breathing deeply. The coherence function was used to assess any correlations. Results: The analysis revealed that for each subject there was a correlation between some components of the pulse and derived heart rate variability, and the aberrations. The particular frequencies and aberrations were subject dependent. The experiments involving changing the properties of the pulse further demonstrated these correlations. Conclusions: The results show that although the pulse plays a role in the dynamic characteristics of the higher–order aberrations, it cannot account for all of them. Hence another as of yet undetermined factor or (factors) is also playing a role.
Keywords: optical properties • refraction • blood supply