Complete blood cell count and retinal vessel diameters

Hemoglobin levels are associated with retinal vascular caliber in a middle-aged birth cohort

Vascular and neural structures of the retina can be visualized non-invasively and used to predict ocular and systemic pathologies. We set out to evaluate the association of hemoglobin (Hb) levels within the national reference interval with retinal vascular caliber, optical coherence tomography (OCT) and visual field (VF) parameters in the Northern Finland 1966 Birth Cohort (n = 2319, 42.1% male, average age 47 years). The studied parameters were evaluated in Hb quintiles and multivariable linear regression models. The lowest Hb quintile of both sexes presented the narrowest central retinal vein equivalent (CRVE) and the healthiest cardiometabolic profile compared to the other Hb quintiles. In the regression models, CRVE associated positively with Hb levels in both sexes, (Bmales = 0.068 [0.001; 0.135], Bfemales = 0.087 [0.033; 0.140]), after being adjusted for key cardiometabolic and inflammatory parameters, smoking status, and fellow vessel caliber. No statistically significant associations of Hb levels with central retinal artery equivalent, OCT or VF parameters were detected. In conclusion, Hb levels were positively and specifically associated with CRVE, indicating that Hb levels are an independent factor affecting CRVE and the effect is in parallel with established risk factors for cardiometabolic diseases.

Influence of the vessel wall geometry on the wall-induced migration of red blood cells

The geometry of the blood vessel wall plays a regulatory role on the motion of red blood cells (RBCs). The overall topography of the vessel wall depends on many features, among which the endothelial lining of the endothelial surface layer (ESL) is an important one. The endothelial lining of vessel walls presents a large surface area for exchanging materials between blood and tissues. The ESL plays a critical role in regulating vascular permeability, hindering leukocyte adhesion as well as inhibiting coagulation during inflammation. Changes in the ESL structure are believed to cause vascular hyperpermeability and entrap immune cells during sepsis, which could significantly alter the vessel wall geometry and disturb interactions between RBCs and the vessel wall, including the wall-induced migration of RBCs and the thickening of a cell-free layer. To investigate the influence of the vessel wall geometry particularly changed by the ESL under various pathological conditions, such as sepsis, on the motion of RBCs, we developed two models to represent the ESL using the immersed boundary method in two dimensions. In particular, we used simulations to study how the lift force and drag force on a RBC near the vessel wall vary with different wall thickness, spatial variation, and permeability associated with changes in the vessel wall geometry. We find that the spatial variation of the wall has a significant effect on the wall-induced migration of the RBC for a high permeability, and that the wall-induced migration is significantly inhibited as the vessel diameter is increased.

OCTA Derived Vessel Skeleton Density Versus Flux and Their Associations With Systemic Determinants of Health

Purpose

To examine the associations of optical coherence tomography angiography (OCTA)-derived retinal capillary flux with systemic determinants of health.

Methods

This is a cross-sectional study of subjects recruited from the African American Eye Disease Study. A commercially available swept-source (SS)-OCTA device was used to image the central 3 × 3 mm macular region. Retinal capillary perfusion was assessed using vessel skeleton density (VSD) and flux. Flux approximates the number of red blood cells moving through vessel segments and is a novel metric, whereas VSD is a previously validated measure commonly used to quantify capillary density. The associations of OCTA derived measures with systemic determinants of health were evaluated using multivariate generalized linear mixed-effects models.

Results

A total of 154 eyes from 83 participants were enrolled. Mean VSD and flux were 0.148 ± 0.009 and 0.156 ± 0.016, respectively. In a model containing age, systolic blood pressure, diabetes status, hematocrit, and presence of retinopathy as covariates, there was a negative correlation between VSD and age (P < 0.001) and retinopathy (P = 0.02), but not with hematocrit (P = 0.85) or other factors. There was a positive correlation between flux and hematocrit (P = 0.02), as well as a negative correlation for flux with age (P < 0.001), systolic blood pressure (P = 0.04), and diabetes status (P = 0.02). A 1% decrease in hematocrit was associated with the same magnitude change in flux as ∼1.24 years of aging. Signal strength was associated with flux (P < 0.001), but not VSD (P = 0.51).

Conclusions

SS-OCTA derived flux provides additional information about retinal perfusion distinct from that obtained with skeleton density-based measures. Flux is appropriate for detecting subclinical changes in perfusion in the absence of clinical retinopathy.

The association between markers of inflammation and retinal microvascular parameters: A systematic review and meta-analysis

BACKGROUND AND AIMS

Adverse changes to the microcirculation play an important role in the pathogenesis of cardiovascular disease (CVD), and inflammation is a key causal mechanism. We investigated the relationship between inflammatory markers and retinal microvascular parameters.

METHODS

Studies up to April 2021 were identified in Medline, Embase and PubMed with the following terms: retinal microvascular parameters, inflammatory markers, and observational studies. Correlation coefficients of inflammatory markers and retinal vascular caliber were pooled using the random-effects model.

RESULTS

Of 4783 studies identified, 36 met the inclusion criteria (general population 26, patients with diseases 10). C-reactive protein (CRP) and white blood cell count (WBC) were most frequently reported. We conducted meta-analysis with 12 CRP studies (22422 participants) and six WBC studies (15209 participants), and also performed a narrative review of all studies. There was consistent evidence of a modest association between CRP and venular caliber (r = 0.09, 95%CI 0.05 to 0.12), but little evidence of an association between CRP with retinal arteriolar caliber (r = 0.00, 95%CI -0.02 to 0.02). Similarly, WBC had stronger associations with venular (r = 0.18, 95%CI 0.05 to 0.31) than arteriolar caliber (r = 0.05, 95%CI 0.01 to 0.09). Narrative review of other inflammatory markers showed consistent findings. There was little evidence of associations between inflammation markers and other microvascular parameters, fractal dimension and tortuosity.

CONCLUSIONS

There was more evidence for an association of inflammation with retinal venular than with arterial caliber. The findings suggest a potential druggable mechanism contributing to microvascular damage that has been relatively overlooked in CVD pathogenesis and treatment.

Complete blood count and retinal vessel calibers

Objective

The influence of hematological indices such as complete blood count on microcirculation is poorly understood. Retinal microvasculature can be directly visualized and vessel calibers are associated with a range of ocular and systemic diseases. We examined the association of complete blood count with retinal vessel calibers.

Methods

Cross-sectional population-based Blue Mountains Eye Study, n = 3009, aged 49+ years. Complete blood count was measured from fasting blood samples taken at baseline examination, 1992–4. Retinal arteriolar and venular calibers were measured from digitized retinal photographs using a validated semi-automated computer program.

Results

All analyses adjusted for age, sex, systolic blood pressure, diabetes, smoking and fellow vessel caliber. Higher hematocrit, white cell count and platelet count were associated with narrower arteriolar caliber (p = 0.02, 0.03 and 0.001 respectively), while higher hemoglobin, hematocrit, red cell count, white cell count and platelet count were associated with wider venular caliber (p<0.0001 for all). Each quintile increase in hematocrit, white cell count and platelet count was associated with approximately 0.5 µm narrower arteriolar caliber; whereas each quintile increase in all of the complete blood count components was associated with approximately 1–2 µm wider venular caliber.

Conclusions

These associations show that elevated levels of hematological indices can have adverse effects on the microcirculation.

Cross-sectional associations of medication and supplement use with retinal vascular diameter in the Beaver Dam Eye Study

IMPORTANCE

Retinal vessel diameters are being measured to examine their relationship with ocular and systemic disease and, in some studies, to calculate the risk of disease. Important factors that directly affect retinal vessel diameters, such as medication use, should be considered when estimating these associations.

OBJECTIVE

To quantify the association between selected medications and supplements and retinal vessel diameters.

DESIGN, SETTING, AND PARTICIPANTS

In a prospective cohort investigation, 4926 participants (aged 43-86 years at baseline) in the Beaver Dam Eye Study were evaluated every 5 years during 20 years of follow-up from 1988 to 2010.

MAIN OUTCOMES AND MEASURES

Central retinal arteriolar equivalent and central retinal venular equivalent measured from the Early Treatment Diabetic Retinopathy Study fundus photograph field 1.

RESULTS

After Bonferroni correction, the use of any blood pressure medication (β = 0.75; P = .04), specifically calcium channel blockers (β = -1.02; P < .001), was significantly associated with wider central retinal arteriolar equivalent adjusting for refraction, photograph focus, age, systolic blood pressure, height, examination phase, educational level, smoking and drinking histories, and presence of diabetes mellitus and emphysema. Use of prostaglandin analogues was marginally associated with narrower central retinal arteriolar equivalent (β = -2.04; P = .09); β-blockers (β = -1.02; P = .10) and oral corticosteroids (β = 2.13; P = .07) were marginally associated with changes in the central retinal venular equivalent.

CONCLUSIONS AND RELEVANCE

Several medications are associated with central retinal arteriolar and venular equivalents. Prostaglandin analogues, calcium channel blockers, and oral corticosteroids have the largest relative effects. After Bonferroni correction was applied, the use of calcium channel blockers was most strongly associated with change in the central retinal arteriolar equivalent. The presence of factors that are associated with retinal vessel diameters should be considered when using retinal vessel diameter as an outcome or when using these measures to assess the risk of systemic or ocular disease.

Determinants of retinal venular diameter: the Beaver Dam Eye Study

OBJECTIVE

To describe how retinal venular diameter changes over time for an individual and to examine differences in these changes among people with different risk profiles.

DESIGN

Population-based cohort study.

PARTICIPANTS

A total of 4600 persons aged 43 to 86 years from the Beaver Dam Eye Study (BDES) who participated in at least 1 examination and had venular diameter measured in the right eye.

METHODS

Data from 4 examinations during a 15-year period were analyzed. Retinal venular diameter was measured from photographs at each examination by computer-assisted methods and summarized as the central retinal venular equivalent (CRVE). Associations of risk factors with concurrent CRVE measurements and changes in CRVE over time were determined using multivariate analyses.

MAIN OUTCOME MEASURES

Central retinal venular equivalent.

RESULTS

The CRVE tended to narrow with age. Mean CRVE was approximately 5 μm smaller (225 vs. 230 μm) for the average 70-year-old compared with the average 50-year-old, and was approximately 13 μm smaller (217 vs. 230 μm) for the average 85-year-old compared with the average 50-year-old. Male sex (beta estimate [β] = 5.24; 95% confidence interval [CI], 3.58-6.90), history of current cigarette smoking (β = 9.38; 95% CI, 8.26-10.49), and higher white blood cell (WBC) count (per 1000/μL: β = 0.95; 95% CI, 0.74-1.16) were independently associated with larger concurrent CRVE, whereas higher mean arterial blood pressure (per 5 mmHg: β = -0.36; 95% CI, -0.50 to -0.23) and higher serum high-density lipoprotein (HDL) cholesterol (per 10 mg/dl: β = 0.89; 95% CI, -1.15 to -0.63) were independently associated with smaller concurrent CRVE. History of cardiovascular disease (CVD) (β = -0.16; 95% CI, -0.26 to -0.06) and presence of chronic kidney disease (CKD) (β = -0.20; 95% CI, -0.34 to -0.05) were associated with a greater decrease in CRVE over time.

CONCLUSIONS

These data show that retinal venular diameter tends to narrow with age; concurrent venular diameter is independently associated with sex, blood pressure, serum HDL cholesterol, WBC count, and history of current cigarette smoking; and change in CRVE is independently associated with a history of CVD and presence of CKD. The different independent effects of these interrelated factors on CRVE highlight the complex relationship between CRVE and systemic diseases and conditions and the difficulty in determining specific causes of change in CRVE over time.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.