Current perspective on microfluctuations of accommodation.

The collaboration of Fergus Campbell, Gerald Westheimer and John Robson in the 1950s produced insight into the nature of accommodation microfluctuations and instigated work which has led to the current view that the nominally steady-state accommodation response exhibits temporal variations which can be characterized by two dominant regions of activity: a low-frequency component (LFC less than 0.6 Hz) and a high-frequency component (HFC greater than or equal to 1.0 less than or equal to 2.3 Hz). A functional role has been attributed to these microfluctuations as they offer a means by which a directional cue could be derived from an even-error stimulus. However, there is no consensus regarding the respective contribution made by each of the dominant components in the accommodation control process. Using a newly-designed measurement and recording system we have conducted a series of experiments to investigate the nature and aetiology of the microfluctuations. The incidence and magnitude of microfluctuations in LFCs and HFCs for central and peripheral lens zones were investigated while five young emmetropic subjects viewed a near target. The form of the power spectra of the fluctuations was found to be similar for central and peripheral zones although an overall reduction in magnitude was observed in the periphery. The HFCs are thus a consistent feature of microfluctuations in central zones and not, as previously suggested, merely a spurious feature of peripheral zones. A significant between-subject variation in the location of HFCs was found and led us to consider the relationship between HFCs and other physiological systems which provide intraocular rhythmic variation.(ABSTRACT TRUNCATED AT 250 WORDS)