Microfluctuations of accommodation and spherical aberration

The microfluctuations of steady-state accommodation occur at frequencies up to about 1.5 Hz, with characteristic high and low frequency components. The high frequency components (HFC) of microfluctuations have been linked to arterial pulse (M'inn et a1 1990, Owens et a1 1991 and Collins et al 1995) and therefore should not actively change characteristics as a result of changes in visual stimulus conditions. On the other hand, if the low frequency components (LFCs) contribute to steady-state accommodation control, they might be predicted to increase in amplitude in degraded stimulus conditions and when the depth of focus of the eye is increased. Spherical aberration increases the depth of focus of the eye and was systematically varied (induced spherical aberration of t1.1 D and t2.2 D at the edge of a 5 mm pupil) to investigate its influence on accommodation microfluctuations. At the same time, the subjects' pulse rates were measured and the subjects breathed at a fixed respiration rate to accurately identify their contributions to the accommodation microfluctuations. The results for the two subjects showed the expected correlation between the HFC of the steady state microfluctuations and the subjects' pulse rates. Similarly, there was a clear association behveen a LFC peak of the power spectra corresponding to respiration frequency and a rhythm of the steady state microfluctuations. However, there was no significant change in the microfluctuation power spectra associated with changes in spherical aberration. It seems possible that all components of accommodation microfluctuations may be independent of retinal feedback