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Editors Selection IGR 12-4
Medical Therapy: Asymmetry of IOP reduction in fellow eyes
Comment by Robert Fechtner on:
46626 Asymmetry of 24-Hour Intraocular Pressure Reduction by Topical Ocular Hypotensive Medications in Fellow Eyes, Liu JHK; Realini T; Weinreb RN, Ophthalmology, 2011; 118, 1995-2000
Are you still doing monocular trials? I used to instruct my residents and fellows to use monocular trials to determine if a medication was effective at lower IOP. Then Tony Realini challenged my tradition and set about systematically exploring the underlying assump- tions. Subsequent collaborations have dashed all the assumptions upon which my teaching had been based.
IOP reductions ensuing from bilateral therapy are not substantially symmetric between fellow-eye pairs
One of the first assumptions of the monocular trial is that fluctuation is symmetric between eyes. Any relative change between eyes could be attributed to medication effect. But fluctuation of IOP is not symmetric (Realini 2010, 2011). Even if this assumption were true, the next key tenets of the monocular trial is symmetry of therapeutic response to medications. If the first eye responds, the medication is added to the second eye without a formal evaluation of therapeutic efficacy. In retrospective and prospective studies of monocular trials the first eye response was not highly predictive of the second eye response (Realini 2004, 2009). The current study by Liu et al. (1495) demonstrates asymmetry of IOP reduction in eyes receiving bilateral monotherapy or adjunctive therapy during a 24-hour period in a sleep laboratory. Measurements of IOP were obtained every two hours. There was only a weak association between right and left eye responses to medication when single paired IOP data were considered. Averaging IOP values from different time points within a specified time period (the diurnal times or the nocturnal times for example) improved concordance of inter-eye IOP responses, though only modestly.
To characterize both IOP and it's response to therapy, we need multiple measurements at multiple times
This study demonstrates that IOP reductions ensuing from bilateral therapy are not substantially symmetric between fellow-eye pairs. None of the assumptions of the monocular trial have been supported in systematic series of publications further enhanced by the current study. If there is no evidence to support the use of the monocular trail, how can we assess efficacy of medical therapy to lower IOP? To characterize both IOP and it's response to therapy, we need multiple measurements at multiple times. It is not yet clear what the optimal times and frequency of sampling might be.
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