The difference of ocular measures and cardiometabolic risk factors was assessed by the t-test and χ2 test between hypertensives and normotensives.
The association between hypertension and macular thickness at each subfield was evaluated using a linear mixed regression analysis, in which the correlation structure from the intrafamilial relationship was accounted for by adjusting for household effect and sibling effects as random effects.
12 Prior to linear mixed regression analysis, macular thickness data at each subfield were log transformed because they did not show normal distribution. Initially, we did analysis with consideration of age, sex, and axial length as fixed effects. In the next step, we made further adjustment for known cardiometabolic risk factors, such as BMI, LDL-C, HDL-C, diabetes, and smoking, as fixed effects.
We also evaluated the independent association of macular thickness with other cardiometabolic risk factors, such as BMI, LDL-C, HDL-C, diabetes mellitus, and smoking, also by linear mixed regression analysis.
In addition, to evaluate whether the association between hypertension and macular thickness is influenced by the presence of other cardiometabolic risk factors or not, we conducted stratified analysis. For this analysis, subjects were categorized into two strata for each cardiometabolic risk factor: BMI (≥25, <25 kg/m2), LDL-C (≥3.36, <3.36 mM), HDL-C (≥1.03, <1.03 mM for men, and ≥1.29, <1.29 mM for women), glucose (≥5.55, <5.55 mM); and smoking (ever, never). For glucose, we applied the cutoff level of 5.55 mM used for diagnosing metabolic syndrome instead of the cutoff level for diagnosing diabetes because the number of subjects with diabetes was too small (67 persons) to conduct stratified analysis.
All the hypotheses were tested bidirectionally with an alpha level set at 0.05. All the analyses were conducted with statistical software (SAS version 9.3; SAS Institute, Inc., Cary, NC, USA).