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Mengfei Wu, Mengling Liu, Katie Lucy, Hiroshi Ishikawa, Joel S Schuman, Gadi Wollstein; Applying Propensity Score in Assessing Association of Glaucoma Medication with Structural Progression. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1248.
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© ARVO (1962-2015); The Authors (2016-present)
When assessing treatment effects in observational studies, the propensity score (PS) method is commonly used to reduce the selection bias of treatments. Weighting subjects by the inverse probability of treatment using the PS mimics treatment randomization. Our goal was to apply PS to assess the association of glaucoma treatment medication with rates of structural changes in a longitudinal cohort of glaucoma subjects.
Glaucoma subjects treated with prostaglandin, beta blockers, and/or carbonic anhydrase inhibitors (CAIs) with ≥ 2 visits with qualified OCT (Cirrus HD-OCT; Zeiss) were included. Subjects were on medication for at least 3 months prior to each OCT visit. Multinomial PS for baseline medication selection was estimated by baseline age, visual field (VF) mean deviation (MD), intraocular pressure and ethnicity. Rates of change for OCT’s average circumpapillary retinal nerve fiber layer (RNFL) and macular ganglion cell-inner plexiform layer (GCIPL) thicknesses were calculated per eye using linear regression. Their associations with baseline RNFL, GCIPL, baseline medication, post-baseline medication and medication duration were tested using linear regression with and without PS weighting.
207 eyes (117 subjects) were qualified with average age of 62.2±12.7 years and median MD of -3.6 dB (IQR -9.0, -1.4) at baseline, and a mean follow-up of 3.2±1.8 years. The average duration of treatment range from 1.3±1.8 to 2.4±2.5 years for CAIs and prostaglandin, respectively. At baseline, average RNFL and GCIPL were 71.5±14.4 µm and 65.9±13.5 µm. Throughout follow-up, mean rate of change for RNFL and GCIPL were -0.30±2.60 µm/year and 0.27±7.72 µm/year. Without PS weighting, no medication effect was shown to be associated with either rate of change. With PS weighting, however, the rate of change for RNFL was significantly associated with taking CAIs (-1.26 µm/year, p=0.029) and prostaglandin (-0.98 µm/year, p=0.044) and baseline RNFL (-0.05 µm/year, p=0.017). Longer use of the medications slowed RNFL decrease, although the effects were not statistically significant. No association was detected between treatment and rate of change for GCIPL.
PS can be useful to reduce treatment selection bias and facilitate more rigorous estimation of medication effects in observational glaucoma research.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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