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Ilana Forchheimer, Joshua A. Young, Carlos G. De Moraes, Christopher C. Teng, Celso Tello, Robert Ritch, Jeffrey M. Liebmann; Development of a Mathematical Model to Predict Intraocular Pressure (IOP) Variability in Untreated Ocular Hypertensives (OHTN). Invest. Ophthalmol. Vis. Sci. 2011;52(14):659.
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To determine if IOP variability follows a statistically normaldistribution in untreated OHTN patients.
56 eyes of 28 subjects diagnosed with OHTN seen in a glaucomareferral practice were included. Patients were included if theyhad at least 20 IOP measurements in each eye and no historyof topical or oral IOP lowering therapy. The statistical programAnalyse-it was used to graph the data, plot the best fit normalcurve and create a normality plot (Q-Q plot) for the set ofdata points from each eye. A Shapiro-Wilk statistic was alsocalculated for each eye to determine which eyes did not distributenormally.
We plotted each set of IOP values against the best fit normalcurve and found the data to closely approximate the normal curve(Figures 1 and 2). When a linear regression analysis was plotted,the data points again appeared to closely match a best-fit normalcurve. Of the 56 eyes, 15 (26.8%) did not follow a normal distribution.Of these 15 eyes, 6 were from 3 patients.
The variability of IOP measurements in untreated OHTN tendsto have a normal distribution. This finding is important asprobabilistic models that are predicated on a normal distributionmay be applied to the set of pressures obtained from a singlepatient. Therefore, it is possible to develop a mathematicalmodel that can estimate IOP variability based on these findings.
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