Data analysis
±, CRVE, CRAE, SDB
REGRESSION
All statistical analyses were performed using SPSS version 24.0 (IBM SPSS Statistics for Windows, Version 24.0. Armonk, NY: IBM Corp.).Main and RFM/CPAP Sub-Group data were expressed as mean (± standard deviation) or median (interquartile range) for continuous variables, and frequency and percentage for categorical variables. Spearman’s rank-order correlation were used to test for relationships between continuous variables. Differences between the Main Group and RFM/CPAP sub-group were tested using independent sample t-tests or Mann-Whitney U tests for continuous variables, and Chi-Square tests for categorical variables. A paired t-test was used to examine overnight change (morning minus evening) in CRAE and CRVE (ΔCRAE; ΔCRVE, respectively).Backwards, stepwise, multiple linear regression (variables removed at p>0.1) was used to establish predictive variables for retinal vessel size and overnight change using a strategy of first establishing non-SDB related predictive factors operating in the data set (Base Models) and then assessing the impact of adding individual SDB-variables to the base models (SDB Variable Models).Non-SDB variable predictor candidates were identified in two ways: 1) from published models for retinal vessel size [SDB variables were skewed (Kolmogorov-Smirnov Test for Normality) and, therefore, log transformed (e.g. ln AHI+1) before being individually added to the base models as required. Any improvement in the model RFor the RFM/CPAP intervention study, paired t-tests were used to identify differences in retinal vessel diameter size (ie evening CRAE, CRVE and overnight change in CRAE/CRVE) over 12 months. Spearman’s Rho rank correlation was used to test for correlations between the change (Δ) in retinal vessel diameter, CPAP use, Δ base model variables (age, systolic and diastolic blood pressure) and SDB variables. Multiple linear regression analysis was used to establish predictive variables for: 1) Δ evening retinal vessel diameter, and 2) Δ overnight change in retinal vessel diameter.