Discussion
morning CRVE, CRAE, retinal microvascular, CRVE, SDB
RETINAL VASCULAR, OTHER CARDIOVASCULAR DISEASE, RETINA
The primary focus of the present study was to test for relationships, in a non-diabetic sleep-clinic patient cohort, between polysomnography determined SDB severity and retinal micro-vasculature morphology. Overall no such relationships were detected, but when a subgroup enriched with more severe levels of SDB was examined, a greater AHI value was associated with a larger evening-measured CRAE value. However, the effect size for this relationship was small, with only a ~2.5 μm (~1.7%) increase in CRAE over the AHI range 5 to 30 events/hr.Our study is unique in that we tested for acute overnight effects of SDB on retinal vascular morphology. While there was no group mean overnight change in CRAE, mean CRVE values measured in the morning, immediately upon awakening, were on average slightly larger than the prior evening values. Multivariable models failed to identify predictors for this outcome, except in a sub-group characterised by more severe SDB, where older individuals had less of an overnight change in CRVE. Another feature of our experimental design was a 12 month monitored RFM/CPAP intervention phase characterised by relatively high rates of compliance. In the subgroup enrolled in this part of the study, across the RFM/CPAP period, there were no detected group mean changes in CRAE or CRVE evening values. However, individuals with more severe SDB had a decreased evening CRVE and, correspondingly, an increased overnight change in CRVE after 12 months of RFM/CPAP treatment.In addition, this is the first study to demonstrate an effect of sleep, or circadian variation, on retinal vascular morphology. There is a small difference in morning CRVE compared to the evening CRVE, and this change increases in those with more severe SDB after treatment. Circadian changes in the retina have long been recognised [In this study any identified impacts of SDB severity on retinal vascular morphology were all characterised by effect sizes that were relatively small. Therefore, in this non-diabetic cohort, where other cardiovascular disease risk factors were minimised/controlled, it seems unlikely that such associations reflect a major pathophysiological interaction between SDB and retinal microvascular morphology.