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S. Rosner, P.J. Gomes, MS, M.B. Abelson, MD; The Effect of Absolute Versus Relative Pollen Counts on Individuals' Ocular Itching Severity Scores in Six Different Geographic Locations . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3766.
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Purpose: The levels of environmental pollens are generally considered a determinant of the magnitude of a person's ocular allergy response. Pollen levels are specific to the environment of an individual geographic area. The purpose of this investigation was to compare the effects of absolute levels of pollen on severity of ocular itching among several geographic locations. Methods: The study population was derived from an environmental clinical study with subjects in 6 different geographical locations (Rochester, NY; Austin, TX; Creve Coeur, MO, Charlotte, NC; North Andover, MA; Bel Air, MD). Subjects assessed itching severity (0-4 scale) over a total of 12 visits. Ragweed pollen levels were stratified into four quartiles for each site. The analysis focused on those visits that occurred in the highest range of ragweed pollen levels (ie. the 4th quartile). Average itching scores for visits occurring on days in the highest pollen count quartile at each site were compared using ANOVA. Results:A total of 214 visits occurred during days falling in the highest ragweed count quartile for all the sites. Across all sites, for the highest exposure quartile, the average ragweed pollen counts measured twenty-four hours prior to the study visit were: 274.5 g/m3, Rochester, NY; 414.9g/m3, Austin, TX; 143.4 g/m3, Creve Coeur, MO; 102.1 g/m3, Charlotte, NC; 18.0 g/m3, North Andover, MA; 27.5 g/m3, Bel Air, MD. The average twenty-four hour itching severity scores for the visits occurring on days in the highest exposure quartile for each site, respectively, were 1.20, 0.75, 0.98, 0.95, 1.17, and 0.83 (p=0.2888). Analysis of all four quartiles revealed a trend in itching severity: as pollen level increased (by quartile), greater percentages of patients indicated itching severity >1. Conclusions: Although the absolute ragweed pollen counts in the highest exposure quartile are very different between sites, there is no significant correlation within the highest quartile with itching. A numerical trend exists demonstrating that itching in the highest quartile may be greater than that in the lowest. These results suggest that ocular itching severity is determined more by the relative pollen levels within a geographic location than by the absolute pollen count.
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