Microfluctuations in accommodation: an update on their characteristics and possible role

Purpose Following the recognition, some 80 years ago, that the accommodation of the eye is not stable but fluctuates over a range of about ±0.5 D, mainly at frequencies of up to a few Hz, there has been a continuing interest in the characteristics of these microfluctuations (MFs) and their possible role in the control of accommodation. This paper reviews relevant work carried out since 1988, when we previously reviewed the same topic (Charman WN, Heron G. Fluctuations in accommodation: a review. Ophthalmic Physiol Opt 1988; 8: 153–164). Recent findings Studies relating to the effects on the MFs of stimulus form, luminance and vergence are described, together with those of pupil diameter, age and ametropia. Important advances in the understanding of the links between the characteristics of the MFs and those of the cardiopulmonary system, higher-order aberrations and ocular depth-of-focus are outlined. Only limited progress has been made in understanding the role of MFs in accommodation control. Summary While the dependence of the characteristics of the MFs in relation to observing conditions is now reasonably well understood, their involvement in accommodation control still needs clarification. The current consensus appears to be that any role is more likely to be concerned with maintaining an appropriate response, rather than in initiating responses to abrupt changes in stimulus vergence. Fluctuations at lower temporal frequencies (<0.6 Hz) are probably important to the control process, which may make use of the associated changes in the contrast and spatial frequency spectrum of the retinal image.