Although structural metrics of the retinal arterioles differed between the diabetes and control groups, there was a large amount of overlap. This is not surprising, because participants with diabetes are often highly variable in their systemic control, duration of disease, therapeutic interventions, and overall response to diabetes.
40 Whereas it could be that the variability in our vessel metrics differed widely between individual blood vessels, the iAIR indicates that a large amount of the variability was related to the individual. In
Figure 3, we highlight vessel measurements from 2 individuals with very different iAIRs: one individual with a more deviated iAIR of 0.88 and the second individual with an iAIR of 1.06 that is more like that of the average control iAIR of 1.02 in this study. Data from these 2 individuals are plotted in
Figures 3A and
3B. The individual with the iAIR of 0.88, in general, has thicker walls and increased WLRs and, at the time of imaging, was a 42-year-old man with newly diagnosed with type 2 DM. Clinically, this individual had mild NPDR and self-reported that their last glycosylated hemoglobin (HbA1C) was 9 about 2 weeks prior to the imaging session. They also had controlled hypertension. Conversely, the individual with the iAIR of 1.06 was a 50-year-old woman, had no DR, and a reported HbA1C of 5.6. This individual had a 27-year history of type 2 DM and was extremely well controlled since receiving their initial diagnosis and treated with metformin and liraglutide. Additionally, this individual was also being treated with lisinopril despite having never received an official diagnosis of HTN. Although no concrete conclusions can be made, it is speculative whether the tight control and good compliance with antidiabetic medications enabled the individual with the iAIR of 1.06 to maintain, or perhaps even reverse, arteriole remodeling within their retina. With systemic hypertensive therapy, it has been shown that reverse remodeling with decreased MLR of subcutaneous arterioles in non-insulin–dependent diabetes mellitus (NIDDM) after 1 year of treatment occurs.
8 Likewise, decreases in WLR with antihypertensive treatment is also observed in retinal arterioles.
41,42 It will be important for future studies to understand the impact of antidiabetic and antihypertension medications on retinal vascular remodeling and the rapidity with which this occurs. This could provide insight as to whether some medications might have a more positive impact on the retinal vascular structure than others in participants with DR or increased risk factors for DR. Last, although the iAIR in the individual with an iAIR of 0.88 was deviated, some individual vessels in this participant are similar, or overlap with, that observed in the healthy controls. As this participant did have clinical DM, whereas the current protocol was not designed to address this, investigating the variability within individuals and relationship of remodeled arterioles spatially to local retinopathic changes may provide an opportunity for the AIR to provide both a global (iAIR) and a local metric of retinal health (AIR of individual arterioles). These two participants display the issue of making vascular measurements on a population with a wide range of histories and supports the need for future studies with larger numbers of participants with well characterized medical histories to better determine the risk factors associated with alterations of the microvasculature due to diabetes.