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Claude F. Burgoyne; Intraocular Pressure (IOP) Magnitude and Fluctuation as Predictors of Optic Nerve Head (ONH) and Retinal Nerve Fiber Layer (RNFL) Structural Change in Monkey Experimental Glaucoma (EG). Invest. Ophthalmol. Vis. Sci. 2011;52(14):658.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the independence of IOP magnitude and fluctuation as risk factors for global Confocal Scanning Laser Tomography (CSLT) ONH surface and SDOCT RNFL change within the post-laser data of 46 monkey EG eyes.
Standard testing sessions occurred 3-5 times when normal and every 1-3 weeks post-laser - induced EG until sacrifice. Tonopen measurement of IOP (mean of n=3 per eye) occurred at the start of each testing session after a variety of anesthesia regimens. CSLT/SDOCT imaging was performed 30 minutes after IOP was set to 10 mm Hg by anterior chamber manometer. Post-laser sessions were split into fixed length ‘windows’ of consecutive imaging sessions, (3 to 11 sessions per window). IOP magnitude and fluctuation were characterized by calculating standard deviation (IOPSD), difference (IOPDiff, max - min IOP), mean (IOPMean), and maximum (IOPMax) and the root-mean-squared residual (IOPRMSR) from the trend over time, within each window. We assessed whether different IOP characterizations were related to IOPMean, using a generalized estimating equation (gee) linear regression model to account for multiple windows from the same eye. Univariate and Multivariate gee models were then constructed to assess the effect of the least correlated measures of IOP magnitude and fluctuation on the CSLT Mean Position of the Disc (MPD) and peripapillary circle scan SDOCT RNFL thickness (RNFLT).
All 46 EG eyes had CSLT imaging (n= 937 measures) and 22 of 46 had SDOCT RNFLT imaging (n= 459 measures). The total number of post-laser IOP measures was 1438. Using both overlapping and non-overlapping windows of n=5 post-laser imaging sessions, IOPRMSR/ IOPMean was the characterization of IOP variability that was least correlated to IOPMean (p=0.69 and 0.14, respectively). While IOPMax, IOPMean and IOPRMSR/ IOPMean were statistically significant univariate risk factors for both ONH and RNFL change, IOPMax was the only independent risk factor within a trivariate analysis.
Within this untreated, variably-anesthetized, inter-session IOP data from 46 monkey EG eyes, IOPRMSR/ IOPMean was the IOP fluctuation parameter that was least correlated with IOPMean and IOPMax. However, even in this setting, IOPMax was the best predictor of both forms of structural change and neither IOPMean nor IOPRMSR/ IOPMean added significant additional information. While IOP fluctuation was not an independent risk factor for structural change, this may change when continuous high frequency IOP measurement is achieved.
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