Compared with emmetropes, myopes have an increase in myopic refractive status, and are usually accompanied with an increase in axial length.
30 Both refractive error
17,18 and axial length
15 can affect the mfERG response in myopic adults. In essence, compared with axial length, refractive error was found to account for a greater proportion of the variability in mfERG response measured with conventional stimulation in myopic adults.
16 The authors hypothesize that these two factors will also operate similarly in children. A hierarchical regression model not only evaluates the potential effects of sets of independent variables (i.e., refractive error and axial length) on dependent variables (i.e., mfERG response), it also evaluates the individual effect of each independent variable. Since refractive error has a greater impact than axial length on the mfERG response in adults,
16 a hierarchical regression model was used to first evaluate the effect of refractive error on the global flash mfERG response; then, the combined effect of refractive error and axial length on the global flash mfERG response was evaluated.
19 Bonferroni correction was used to correct the level of significance due to multiple comparisons across different retinal regions; that is, the level of significance was set at 0.01. Because there was a substantial correlation between refractive error and axial length, these two factors have been tested and passed for the assumption of multicollinearity and the variance inflation factor of the multiple regression models.
31 These tests were used to avoid any redundant, independent factors put into the models. Statistical Package for the Social Sciences (SPSS 15.0; SPSS Inc., Chicago, IL) was used to perform all statistical testing.