Purpose:
It is generally stipulated that occlusion therapy be undertaken during waking hours but within this typically 8–10 hour period the time of day at which patching commences is at parental discretion. We sought to identify, by objective means, whether or not occurrences of patching are uniformly distributed over waking hours.
Methods:
The Monitored Occlusion Treatment of Amblyopia Study (Stewart et al., Invest. Ophthalmol. Vis. Sci. 2004;45:3048–54) examined the dose–response relationship of occlusion therapy. All final phase participants (n=72) had their prescribed dose (6 hrs/day) monitored using an occlusion dose monitor (ODM). This device consists of a data logging unit worn around the child's neck or waist connected via a plastic encapsulated lead to two miniature electrodes incorporated into the under–surface of a modified eye patch (Fielder et al., 1994; Lancet 343:547). In addition to the facility to record objectively the duration of all patching episodes (resolution = 60s), the real–time onset and offset of each individual episode was logged.
Results:
A plot of the minutes of recorded patching as a function of time–of–day approximated to a symmetrical bell–shaped distribution with a peak at 12:00 (>100,000 minutes) and a minimum at 24:00 (<1000 minutes).
Conclusions:
In a large sample of clinical study participants, episodes of patching were not uniformly distributed over waking hours. There exist a number of physiological variables that exhibit a circadian periodicity (e.g. cerebral blood flow) which could conceivably influence the efficacy of occlusion. Objective monitoring of occlusion provides a means by which such putative relationships can be explored.
Keywords: amblyopia • clinical (human) or epidemiologic studies: treatment/prevention assessment/controlled clinical trials