A Model to Estimate the Unmedicated Intraocular Pressure of Patients on Glaucoma Medications

Précis: This report presents a model which can be used to determine the IOP-lowering effect of a glaucoma procedure or treatment when a medication washout is not ethical or not possible to be performed. Background: The effect of individual (or certain predefined combinations of) glaucoma medications on intraocular pressure (IOP) has been well documented in various clinical trials. Conversely, the cumulative effect of several glaucoma medications, let alone their discontinuation (i.e. washout), on IOP is still relatively unknown. This is why it is generally recommended to perform a medications’ washout to analyze the effect of glaucoma procedure without confounding factors. However, a washout is not always possible or ethical for some patients and can also increase the costs and complexity of clinical trials. Aims: To build and validate a mathematical model of the IOP change after glaucoma medications washout. Method: A literature search was conducted to identify studies reporting IOP values before and after washout, as well as the number of glaucoma medications used. Based on this, a quadratic equation was fitted to estimate the IOP change after washout, using the mean medicated IOP and the mean number of medications as input parameters. Findings: A total of 31 groups (each group having a precise mean medicated IOP, mean number of medications, and mean post washout IOP) from 15 studies were selected to build and validate the model. Overall, over 90% of the variability of IOP change reported in the studies was explained by the model (R2=0.9007). The mean difference between the IOP changes estimated by the model and the IOP changes reported in the studies was less than 1 mmHg. Conclusion: Estimating the IOP change using this model may represent an useful tool to determine the IOP-lowering effect of a glaucoma procedure or treatment when the washout is not ethical or not possible to be performed on patients. More studies need to be conducted to validate the practical robustness of this formula.