IOP reductions from topical medication are unequal in paired eyes

A core assumption for the one-eye therapeutic trial of ocular hypotensive medications is the symmetrical reduction of IOP in paired eyes. In this retrospective study, researchers evaluated this assumption for 24-hour IOP reduction in 118 patients aged 41 to 79 years with POAG or ocular hypertension who underwent monotherapy or adjunctive therapy. They found only a weak association between right- and left-eye responses to monotherapy or adjunctive therapy when single-pair IOP data are considered. However, considering the averages of multiple paired IOP responses improved the strength of the association.

IOP measurements were obtained every two hours in a sleep laboratory before and after at least four weeks of treatment. Single pair IOP responses from all time points revealed poor symmetry between the two eyes. However, when the average differences in the paired IOP reductions were analyzed for a specific period and posture, the asymmetry decreased. The asymmetry of IOP reduction in the paired eyes was more marked in the sitting position.  Averaging the paired response over a 24-hour period decreased this asymmetry but did not eliminate it.

The authors note that results obtained from evaluating IOP reduction in paired eyes in a clinical setting can be more variable than those obtained in a lab due to influences on IOP on different days and different times. These influences can be physiological or environmental and unrelated to the IOP-lowering efficacy of the drug. To reduce the impact of these variables, they recommend using the method in this study: considering the average IOP response based on multiple IOP measurements taken over several hours on the same day and in defined posture situations.