Relationship between fixation stability measured with MP-1 and reading performance

Background: People with visual impairment have reduced reading performance, which is thought to be related to unstable or eccentric fixation. New microperimeters such as the MP-1 offer straightforward analysis of fixation stability. The aim of this study was to investigate the relationship between fixation stability and reading speed in a large cohort of people with diverse causes of visual impairment and to verify the correlation between reading speed and different methods for the quantification of fixation. Methods: The better eye of one hundred and twenty subjects was assessed. Fixation values were obtained from the MP-1 microperimeter. Reading speed was evaluated using newspaper text with magnifiers if required. Results: The poorest fixation stability and reading performance was found in people with age-related macular degeneration while the best fixation was in retinitis pigmentosa subjects. A linear relationship was found between reading speed and the proportion of fixations within 2° (r2 = 0.51, p < 0.001) and 4° (r2 = 0.36, p < 0.001). A negative correlation was found between reading speed and all three bivariate contour ellipse areas (BCEA; for log transformation of 1-S.D., 2-S.D. and 3-S.D.: r2 = 0.39, p < 0.001). In a multiple regression model, proportion of points falling within 2° and 4° circle was significantly related to reading speed (r2 = 0.55, p < 0.01; r2 = 0.43 p < 0.01); also BCEAs values were strongly related to reading ability only in patients with central vision loss (r2 = 0.62, p < 0.01 for LogBCEA 68.2%; r2 = 0.61, p < 0.01 for LogBCEA 95.4% and 99.6%) and peripheral defect (r2 = 0.52, p < 0.01 for LogBCEA 68.2%; r2 = 0.50, p < 0.01 for LogBCEA 95.4%; r2 = 0.49, p < 0.01 for LogBCEA 99.6%) but not in combined defect subjects. Conclusions: The study confirms that in people with visual impairment the reduced reading performance is correlated with fixation instability. Moreover, there is a strong relationship between reading speed and both the proportion of fixations falling within 2° and 4° and bivariate contour ellipse area values.