Microfluctuations of accommodation and spherical aberration

Abstract

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.