The clinical assessment of retinal microvascular structure and therapeutic implications

The Association of Type 2 Diabetes Mellitus with Cerebral Gray Matter Volume Is Independent of Retinal Vascular Architecture and Retinopathy

It is uncertain whether small vessel disease underlies the relationship between Type 2 Diabetes Mellitus (T2DM) and brain atrophy. We aimed to study whether retinal vascular architecture, as a proxy for cerebral small vessel disease, may modify or mediate the associations of T2DM with brain volumes. In this cross-sectional study using Magnetic Resonance Imaging (MRI) scans and retinal photographs in 451 people with and without T2DM, we measured brain volumes, geometric measures of retinal vascular architecture, clinical retinopathy, and MRI cerebrovascular lesions. There were 270 people with (mean age 67.3 years) and 181 without T2DM (mean age 72.9 years). T2DM was associated with lower gray matter volume (p = 0.008). T2DM was associated with greater arteriolar diameter (p = 0.03) and optimality ratio (p = 0.04), but these associations were attenuated by adjustments for age and sex. Only optimality ratio was associated with lower gray matter volume (p = 0.03). The inclusion of retinal measures in regression models did not attenuate the association of T2DM with gray matter volume. The association of T2DM with lower gray matter volume was independent of retinal vascular architecture and clinical retinopathy. Retinal vascular measures or retinopathy may not be sufficiently sensitive to confirm a microvascular basis for T2DM-related brain atrophy.

Patch-based automatic retinal vessel segmentation in global and local structural context

In this paper, we extend our published work [1] and propose an automated system to segment retinal vessel bed in digital fundus images with enough adaptability to analyze images from fluorescein angiography. This approach takes into account both the global and local context and enables both vessel segmentation and microvascular centreline extraction. These tools should allow researchers and clinicians to estimate and assess vessel diameter, capillary blood volume and microvascular topology for early stage disease detection, monitoring and treatment. Global vessel bed segmentation is achieved by combining phase-invariant orientation fields with neighbourhood pixel intensities in a patch-based feature vector for supervised learning. This approach is evaluated against benchmarks on the DRIVE database [2]. Local microvascular centrelines within Regions-of-Interest (ROIs) are segmented by linking the phase-invariant orientation measures with phase-selective local structure features. Our global and local structural segmentation can be used to assess both pathological structural alterations and microemboli occurrence in non-invasive clinical settings in a longitudinal study.

Determinants of retinal microvascular architecture in normal subjects

BACKGROUND

Recent studies have shown that changes in the retinal microvasculature predict cardiovascular disease (CVD); however, little is known regarding influences on the retinal microvasculature in healthy people without overt cardiovascular or metabolic disease.

METHODS

We used a semiautomated computerized technique to analyze digitized retinal photographs from a total of 167 healthy people (age range, 45-75 years; 83 female), without clinical CVD, diabetes, or hypertension, randomly sampled from the population-based Beaver Dam Eye Study. We assessed arteriolar and venular narrowing, arteriolar optimality deviation, and other quantitative aspects of the retinal microvasculature.

RESULTS

Arterioles were significantly narrower and longer, had wider branching angles, and were more tortuous than venules. Increased arteriolar length to diameter ratio (an index of ratio arteriolar narrowing) was positively and independently associated with older age and elevated systolic blood pressure. Arteriolar optimality deviation (an index of microvascular endothelial dysfunction) increased with greater body mass index. Current smoking and increased white blood cell (WBC) count was associated with wider venules. After controlling for smoking, WBC was no longer a significant predictor of venular diameter.

CONCLUSIONS

CVD risk factors are associated with retinal microvascular changes in healthy individuals without evidence of CVD, diabetes, or hypertension. CVD risk factors have different influences on the arteriolar and venular bed.