Because the correlations between the two eyes for the refractive
and biometric variables were high (e.g., correlation coefficients
between right and left eyes for spherical equivalents = 0.85,
AL = 0.85, and VCD = 0.86) and the results were similar
between the two eyes, only the data from analyses of the right eye are
presented. Data on noncycloplegic refraction were converted to
spherical equivalent diopters and were based on subjective refraction,
when participants had both subjective and objective refraction, and on
objective refraction, when only that information was available. Overall
agreement between both types of refraction was high.
19
The analysis was conducted as follows. First, univariate associations
between height, weight, and BMI with different ocular biometric
components, refraction, and sociodemographic factors were determined.
Next, simple linear regressions were performed to assess the effect of
height, weight, and BMI (independent variables) on the individual
biometric components and refraction (dependent variables). Multiple
linear regression models were then constructed to evaluate the effects
of height, weight, and BMI on individual biometric components and
refraction, controlling in turn for age and sex; age, sex, and
education; and age, sex, education, and socioeconomic indicators
(occupation, housing, and income). The adequacy of all linear
regression models was assessed by plotting the residuals of the
regression model against the independent variables and also against the
predicted values of the dependent variable (predicted fit). Because
height correlated strongly with weight, they were both entered
simultaneously in regression models to determine whether their effects
were independent of each other. Statistical analyses of the data were
performed on computer with statistical analysis software (SPSS,
Chicago, IL). Results are expressed as means ± SD.
This study was approved by the ethics committee of Singapore National
Eye Center and performed in accordance with the tenets of the World
Medical Association’s Declaration of Helsinki.