Recent research published in Investigative Ophthalmology & Visual Science sought to identify potential factors that may play a role in determining a few key retinal vessel traits.
Before we get to this study, let’s get some background.
Characteristics of retinal vasculature not only shed light on the probability of future eye disease, but are also thought to reflect the dynamics of systemic circulation—having implications in the development of both ocular and systemic diseases.
- In fact: Factors such as aging, hypertension, inflammation, and arteriosclerosis are thought to impact retinal vessel traits.
And, not to be overlooked: Lifestyle factors and habits (smoking, for instance) may also have significant impacts on vessel characteristics, which could have connections to ocular pathology development later on.
Interesting … and this leads to our topic of discussion?
Indeed. Canadian researchers used data from the Canadian Longitudinal Study on Aging (CLSA) to study the connections between various demographic, lifestyle, and health factors on retinal vascular traits.
- As a refresh: The CLSA is a large, national research platform on health and aging that provides researchers with insights on key questions pertaining to biological, medical, psychological, social, lifestyle, and economic components of aging, disability, and disease.
Talk about their investigation.
Researchers conducted both cross-sectional and longitudinal analyses with data collected from 26,076 Canadian adults included in the CLSA study.
Real quick, talk about these patients.
Participants were Canadian adults (aged 45 to 85) who were recruited via random sampling of health databases and random digit dialing of landline phone numbers.
Baseline data was collected through at-home interviews and physical examinations between 2012 and 2015, and follow-up data was collected 3 years after, between 2015 and 2018.
- Inclusion criteria: Participants who lived in the community, spoke English or French, and lived close to the data collection site.
- Exclusion criteria: Cognitive impairment, full-time participation in the Canadian Armed Forces, currently living on a First Nations reserve, living in a long-term care facility, or not being a permanent resident or citizen of Canada.
And the investigation itself?
Retinal images were taken at baseline and at 3 year follow-up, but only images of the right eye were used due to a larger sample size.
- Retinal vessel measurements—diameter, area, and tortuosity —were then obtained using a deep-learning algorithm called Quantitative Analysis of Retinal Vessel Topology and Size (QUARTZ).
Go on …
Focusing on patients who smoked:
- Current smokers were defined as those who currently smoke daily and have smoked at least 100 cigarettes.
- Former smokers were defined as those who had smoked at least 100 cigarettes but have not smoked in the last 30 days.
Other data collected: Included demographics (age, sex, income, and race/ethnicity), alcohol use, and medical diagnoses (heart disease, stroke, diabetes, and blood pressure).
- To note: Retinal vessel diameter, area, and tortuosity data were normalized and multiple linear regressions were conducted to examine cross-sectional and longitudinal associations for each trait.
And what were the findings?
In the cross-sectional analysis, researchers found that smoking was significantly positively correlated to arteriolar diameter and area, while weaker positive associations were also found between smoking and venular diameter and area.
- Thus: Smoking was determined to be associated with larger arteries and veins of the retina.
Consistently: Longitudinal outcomes using data from the 3-year follow-up revealed that smoking was associated with an increase in both arteriolar and venular diameter over time.
What else?
Using both cross-sectional and longitudinal data, no associations were found between smoking and arteriolar tortuosity.
However: Smoking was found to be positively correlated with venular tortuosity—specifically, current smokers displayed a greater degree of venular tortuosity than those who never smoked.
And what was the impact of smoking on retinal vessels?
Smoking appeared to play a role in the widening of retinal vessels.
- The reason: Researchers proposed that the low blood oxygen concentrations brought on by smoking may lead to dilation of the vessels to allow greater blood flow and oxygenation to ocular structures.
Alternatively: Smoking also appeared to cause injury to vessel walls, leading to the release of inflammatory markers.
- To note: Inflammatory markers such as C-reactive protein (CRP) may lead to diminished ability to regulate vessel size.
How does this compare to other lifestyle factors?
In contrast, alcohol use was associated with decreased retinal vessel size. The proposed reason for this: Alcohol consumption activates the sympathetic nervous system and has a direct constricting effect on the smooth muscle of the vasculature.
Any notable limitations?
A few, including that the sample size for the longitudinal aspect of the study was reduced as not all participants returned for the follow-up visit.
Additionally: Data regarding substance use was self-reported, so it was possible that the true number of smokers and their classifications as current, former, and never smokers were not accurately represented.
- The researchers, however, stated that the misclassification was unlikely to alter the data greatly and that their measures of association were conservative.
Take home.
These findings suggest that lifestyle factors—particularly smoking—may impact retinal microvasculature and, as a result, ocular health.
Despite these conclusions, more research is needed on the long-term effects of these retinal vasculature changes and their potential roles in disease etiology as well as on the predictive power of retinal vasculature changes for pathology.