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C.T. Leffler, L. Amini, D. McGrath, R.C. Allen; Interpretation of Monocular Trials of Glaucoma Medications . Invest. Ophthalmol. Vis. Sci. 2003;44(13):98.
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Purpose: To predict the efficacy of topical glaucoma medications based on monocular treatment trials. To specifically test a traditional hypothesis that efficacy following a monocular trial is related to the change in the treated eye minus the change in the untreated eye, where the untreated eye serves as a control. Methods: Based on a review of medical records in a large glaucoma practice, we identified 144 monocular trials with well-documented intraocular pressure (IOP) readings at baseline (IOP1), during the trial (IOP2), and at follow-up (IOP3). Abstracted data included demographic and other clinical findings. Predictors of the IOP response following the trial (IOP3) in the initially treated eye were identified by univariate and multivariable linear regression. Results: In a multivariable analysis, baseline IOP1 and maximal pretreatment pressure accounted for 28% of the variation in follow-up IOP3 (p < 0.001). This analysis highlighted that higher initial pressures are associated with more dramatic pressure reductions. The change in IOP in the treated eye during the trial (IOP2 – IOP1) predicted 52% of the variation in follow-up IOP3. Fifty-eight per cent of the variation in IOP3 was accounted for in a model which included all factors, including the IOP change in the fellow, untreated eye during the trial. Although the IOP change in the untreated eye was statistically significant (p = 0.02), this change explained only 2% of the variance, and the coefficient was small and opposite in sign from that expected under the standard hypothesis. Conclusions: While we have not proposed that monocular trials be abandoned, we have found that the response in the treated eye is the best predictor of the follow-up IOP response after a monocular trial. The traditional teaching that the IOP change in the untreated eye should be subtracted to control for diurnal and other correlated fluctuations does not universally apply, perhaps due to crossover effects, lack of compliance, regression to the mean, observer bias, spontaneous asymmetric pressure fluctuations, and other factors.
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