The monocular trial controversy: a critical review

The utility of the monocular trial to determine the response to topical ocular hypotensive medications has been recently debated. This review provides a critical evaluation of recent studies and discusses factors that affect the accurate determination of medication response.

Recent concerns about the validity of the monocular trial arise from studies reporting a low-to-moderate correlation of intraocular pressure (IOP) response between the first and second eyes to the same topical ocular hypotensive medication. Few studies, however, have addressed the classic monocular trial that adjusts IOP in the trial eye based on IOP change in the fellow eye. Conflicting results from prior studies are due to differences in study question, study design, and method of analysis. Factors such as variability of IOP, diurnal variation, and regression to the mean further complicate the understanding of whether monocular trials or binocular simultaneous trials (i.e. testing each eye separately) are better for determining medication effect.

The issue of whether or not to use the monocular trial remains controversial. A more clear understanding of factors such as nontherapeutic variability of IOP within the same eye and between eyes may elucidate the answer to this question. Further studies of monocular and binocular trials are needed to clarify which method better estimates medication response.