[Retinal vascular signs: a window to the heart?]

There is increasing recognition that coronary microvascular dysfunction also plays an important role in coronary heart disease. Little is known about this aspect of coronary heart disease due to difficulties in studying the coronary microcirculation directly. The retina is a unique site where the microcirculation can be imaged directly, providing an opportunity to study in vivo the structure and pathology of the human circulation and the possibility of detecting changes in microvasculature relating to the development of cardiovascular disease. This review covers the recent progress in research linking retinal vascular signs to coronary heart disease, and finds accumulating evidence that retinal vascular signs may provide a window into the health of the coronary microvasculature. The most widely studied signs, arteriolar narrowing, and more recently, venular dilation, are likely associated with increased risk of coronary heart disease in women, independent of traditional risk factors. Attempts to improve coronary heart disease risk prediction by incorporating retinal vessel calibre size into risk prediction scores complementing traditional algorithms such as the Framingham risk scores have so far been disappointing. Research is ongoing into the predictive utility of other retinal vascular signs. Retinal photography provides long-lasting records that enable monitoring of longitudinal changes in these retinal signs and vascular health. Full English text available fromwww.revespcardiol.org.

Ten-year longitudinal changes in retinal microvascular lesions: the atherosclerosis risk in communities study

OBJECTIVE

There are limited data on the natural history and longitudinal changes of retinal microvascular lesions. We examined 10-year changes in retinal microvascular lesions, focusing on those related to hypertension and shown to predict development of cardiovascular disease.

DESIGN

Prospective cohort.

PARTICIPANTS

We included 1120 middle-aged participants without diabetes of the Atherosclerosis Risk in Communities (ARIC) Study in 1993 to 1995 and again 10 years later in 2003 to 2005.

METHODS

Retinal microvascular lesions were graded from retinal photographs using the same protocol at both examinations, with changes (incidence or disappearance) adjudicated by a side-by-side comparison of photographs. The study sample was stratified by carotid intima media thickness (IMT) and ARIC field center; thus, all analyses were weighted by these factors. Persons with diabetes were excluded because the frequency and pathophysiology of diabetic retinal lesions is different.

MAIN OUTCOME MEASURES

Incidence and disappearance rates of lesions.

RESULTS

The 10-year incidence of focal arteriolar narrowing, arteriovenous (AV) nicking, and retinopathy in persons without diabetes was 3.4% (95% confidence interval [CI], 2.3-4.9), 2.5% (95% CI, 1.6-3.9), and 2.2% (95% CI, 1.3-3.5) respectively. Over the 10-year period, of 32, 219, and 24 eyes with focal arteriolar narrowing, AV nicking and retinopathy at baseline, 50.3% (95% CI, 28.6-71.9), 40.7% (95% CI, 32.7-49.4), and 65.9% (95% CI, 42.4-83.5), respectively, disappeared. Higher baseline plasma fibrinogen and white cell counts were associated with incident focal arteriolar narrowing; antihypertensive medication use was associated with incident AV nicking, and higher diastolic blood pressure, carotid IMT, and white cell counts were associated with incident retinopathy. Higher fasting serum glucose was not significantly associated with incident retinopathy, although this may be related to the small number of lesions (odds ratio, 5.88; 95% CI, 0.74-46.64 per standard deviation difference).

CONCLUSIONS

In this sample of middle-aged adults, new retinal microvascular lesions appeared at a rate between 2% and 4% over 10 years. A high percentage of lesions (≥40%) disappeared over the same period, suggesting considerable remodeling in the retinal microvasculature.

FINANCIAL DISCLOSURE(S)

The authors have no proprietary or commercial interest in any of the materials discussed in this article.

Retinal vascular fractal dimension measurement and its influence from imaging variation: results of two segmentation methods

AIM

To assess the influences of imaging variation (different photographic angle) on the measurement of retinal vascular fractal dimension (D(f)), using two segmentation methods.

MATERIALS AND METHODS

Nonlinear orthogonal projection segmentation (International Retinal Imaging Software-Fractal, termed IRIS-Fractal) and curvature-based segmentation (Singapore Institute Vessel Assessment-Fractal, termed SIVA-Fractal) methods were used to measure D(f) and were assessed for their reproducibility in detecting retinal vessels of 30 stereoscopic pairs of optic disc color images. Each pair was taken from the same eye with slightly different angles of incidence. Each photograph of the pairs had subtle variations in brightness between areas temporal and nasal to the optic disc.

RESULTS

Intragrader reproducibility of D(f) measurement was similar (intraclass correlation 0.81 and 0.96, respectively) for IRIS-Fractal and SIVA-Fractal. Within-image pair Pearson's correlation coefficients (r) of D(f) measurements were moderate for both methods (0.57 and 0.48, respectively).

CONCLUSIONS

Both nonlinear orthogonal projection and curvature-based retinal vessel segmentation methods were found to be sensitive to variations in image brightness, resulting from iris shadowing associated with different angle of photographic incidence.

Four novel Loci (19q13, 6q24, 12q24, and 5q14) influence the microcirculation in vivo

There is increasing evidence that the microcirculation plays an important role in the pathogenesis of cardiovascular diseases. Changes in retinal vascular caliber reflect early microvascular disease and predict incident cardiovascular events. We performed a genome-wide association study to identify genetic variants associated with retinal vascular caliber. We analyzed data from four population-based discovery cohorts with 15,358 unrelated Caucasian individuals, who are members of the Cohort for Heart and Aging Research in Genomic Epidemiology (CHARGE) consortium, and replicated findings in four independent Caucasian cohorts (n = 6,652). All participants had retinal photography and retinal arteriolar and venular caliber measured from computer software. In the discovery cohorts, 179 single nucleotide polymorphisms (SNP) spread across five loci were significantly associated (p<5.0×10⁻⁸) with retinal venular caliber, but none showed association with arteriolar caliber. Collectively, these five loci explain 1.0%–3.2% of the variation in retinal venular caliber. Four out of these five loci were confirmed in independent replication samples. In the combined analyses, the top SNPs at each locus were: rs2287921 (19q13; p = 1.61×10⁻²⁵, within the RASIP1 locus), rs225717 (6q24; p = 1.25×10⁻¹⁶, adjacent to the VTA1 and NMBR loci), rs10774625 (12q24; p = 2.15×10⁻¹³, in the region of ATXN2,SH2B3 and PTPN11 loci), and rs17421627 (5q14; p = 7.32×10⁻¹⁶, adjacent to the MEF2C locus). In two independent samples, locus 12q24 was also associated with coronary heart disease and hypertension. Our population-based genome-wide association study demonstrates four novel loci associated with retinal venular caliber, an endophenotype of the microcirculation associated with clinical cardiovascular disease. These data provide further insights into the contribution and biological mechanisms of microcirculatory changes that underlie cardiovascular disease.

The microcirculation plays an important role in the development of cardiovascular diseases. Retinal vascular caliber changes reflect early microvascular disease and predict incident cardiovascular events. In order to identify genetic variants associated with retinal vascular caliber, we performed a genome-wide association study and analyzed data from four population-based discovery cohorts with 15,358 unrelated Caucasian individuals, who are members of the Cohort for Heart and Aging Research in Genomic Epidemiology (CHARGE) consortium, and replicated findings in four independent Caucasian cohorts (n = 6,652). We found evidence for association of four loci with retinal venular caliber: on chromosomes 19q13 within the RASIP1 locus, 6q24 adjacent to the VTA1 and NMBR loci, 12q24 in the region of ATXN2,SH2B3 and PTPN11 loci, and 5q14 adjacent to the MEF2C locus. In two independent samples, locus 12q24 was also associated with coronary heart disease and hypertension. In the present study, we demonstrate that four novel loci were associated with retinal venular caliber, an endophenotype of the microcirculation associated with clinical cardiovascular disease. Our findings will help focus research on novel genes and pathways involving the microcirculation and its role in the development of cardiovascular disease.

Effect of obesity on retinal vascular structure in pre-adolescent children

OBJECTIVES. In adults, obesity is linked to changes in the retinal microvasculature. Limited research has been conducted into this association in children. We examined in a cohort of pre-adolescents the relationship between body mass index (BMI) and retinal vascular structure, including retinal vessel diameter and retinal vessel fractals, a measure of geometric patterns reflecting vessel density.

METHODS

A population-based study among school children (2 353/3 144 [75.3%], median age, 12.7 years) recruited from a random cluster sample of 21 schools was conducted during 2004-5. Retinal images were taken and vessel diameter and fractal dimension were quantified using computer-based programs following standardized protocols. Anthropometric measures (weight, height, waist circumference, and BMI) were obtained and defined using standardized protocols.

RESULTS

Children with the highest quartile of BMI had narrower retinal arteriolar diameter (2.8 μm narrower, p<0.0001) and wider venular caliber (4.2 μm wider, p=0.001) than those with BMI in the lowest quartile, after adjusting for age, sex, ethnicity, mean arterial blood pressure, iris color, axial length, birth weight and fellow retinal vessel caliber. Obese children had narrower retinal arteriolar diameter (2.8 μm narrower, p=0.01) and wider venular diameter (4.5 μm wider, p=0.01) than in non-overweight/obese children. Retinal fractal dimension was not significantly associated with BMI. Increasing quartiles of waist circumference were also associated with retinal vessel diameter.

CONCLUSIONS

Our data provide evidence of adverse retinal microvascular caliber changes in obese pre-adolescent children, well before the onset of metabolic and cardiovascular disease in adulthood, and support an early, generalized adverse effect of adiposity on microvascular structure.

Lens opacity and refractive influences on the measurement of retinal vascular fractal dimension

PURPOSE

To examine the influence of lens opacity and refraction on the measurement of retinal vascular fractal dimension (Df).

METHODS

  Optic disc photographs (right eyes) of 3654 baseline Blue Mountains Eye Study participants (aged 49-97) were digitized. Retinal vascular Df was quantified using a computer-based program. Summated severity scores for nuclear, cortical and posterior subcapsular (PSC) cataract were assessed from lens photographs. Refraction data were converted to spherical equivalent refraction (SER), as sum spherical plus 0.5 cylinder power. Axial length was measured at 10-year follow-up examinations using an IOL master.

RESULTS

  Mean Df of the retinal vasculature was 1.444±0.023 for 2859 eligible participants. Increasing lens opacity scores were associated with significant reduction in Df (β=-0.0030, p<0.0001). Both cortical and PSC cataract involving central lens area were associated with reduced Df, after controlling for confounding factors (p(trend) ≤0.0105). Increasing myopia severity was associated with reduced Df after adjusting for lens opacity scores and other confounders (p(trend) <0.0001). The slope of Df decrease per SER reduction was 0.0040 in eyes with SER≤-4D, compared to -0.0016 in eyes with SER>-4D. For axial length quintiles, there were no significant differences in mean Df in all groups except a reduction in the fifth quintile (axial length ≥24.15mm) (all p<0.05).

CONCLUSION

  Ocular media opacity independently influenced retinal vascular Df measurement, but we found no evidence supporting any refractive axial magnification effect on this measure. Myopic refraction ≤-4D was associated with a reduction in Df, suggesting rarefaction of retinal vasculature associated with high myopia.

Retinal fractals and acute lacunar stroke

This study aimed to determine whether retinal fractal dimension, a quantitative measure of microvascular branching complexity and density, is associated with lacunar stroke. A total of 392 patients presenting with acute ischemic stroke had retinal fractal dimension measured from digital photographs, and lacunar infarct ascertained from brain imaging. After adjusting for age, gender, and vascular risk factors, higher retinal fractal dimension (highest vs lowest quartile and per standard deviation increase) was independently and positively associated with lacunar stroke (odds ratio [OR], 4.27; 95% confidence interval [CI], 1.49-12.17 and OR, 1.85; 95% CI, 1.20-2.84, respectively). Increased retinal microvascular complexity and density is associated with lacunar stroke.

Retinopathy in persons without diabetes: the Handan Eye Study

PURPOSE

To describe the prevalence and associations of retinopathy in a population-based nondiabetic sample of rural Chinese.

DESIGN

Population-based cross-sectional study.

PARTICIPANTS

We included 6830 Han Chinese aged > or =30 years from 13 villages of Yongnian County, Handan City, Hebei Province, China.

METHODS

All participants underwent a standardized interview and extensive examinations including retinal photography, measurement of blood pressure (BP) and fasting plasma glucose (FPG). Diabetes mellitus was defined as either FPG > or = 7.0 mmol/l, use of diabetic medication or a physician diagnosis of diabetes. Photographic grading of retinopathy followed the modified Early Treatment Diabetic Retinopathy Study classification system. Logistic regression models were used to assess associations of retinopathy.

MAIN OUTCOME MEASURES

Any retinopathy.

RESULTS

The prevalence of retinopathy among participants without diabetes was 13.6% (95% confidence interval [CI], 12.6-14.6%). The age and gender standardized prevalence of retinopathy in the Chinese adult population (aged 30+ years) without diabetes was estimated to be 12.1% (95% CI 11.1-12.9%). Independent risk factors associated with retinopathy were age (odds ratio [OR], 1.02 ; 95% CI 1.01-1.03 per year increase), male gender (male vs. female, OR 1.27; 95% CI 1.08-1.49), higher FPG (OR 1.30; 95% CI 1.11-1.53 per mmol/l increase), higher systolic BP (OR 1.15; 95% CI 1.05-1.27 per 10 mmHg increase) and higher diastolic BP (OR 1.16; 95% CI 1.09-1.22 per 10 mmHg increase).

CONCLUSIONS

Retinopathy was common among rural Chinese adults without diabetes. Its association with FPG and BP suggests that early microvascular damage is occurring at "high normal" levels of blood glucose and BP.

Prediction of incident stroke events based on retinal vessel caliber: a systematic review and individual-participant meta-analysis

The caliber of the retinal vessels has been shown to be associated with stroke events. However, the consistency and magnitude of association, and the changes in predicted risk independent of traditional risk factors, are unclear. To determine the association between retinal vessel caliber and the risk of stroke events, the investigators combined individual data from 20,798 people, who were free of stroke at baseline, in 6 cohort studies identified from a search of the Medline (National Library of Medicine, Bethesda, Maryland) and EMBASE (Elsevier B.V., Amsterdam, the Netherlands) databases. During follow-up of 5-12 years, 945 (4.5%) incident stroke events were recorded. Wider retinal venular caliber predicted stroke (pooled hazard ratio = 1.15, 95% confidence interval: 1.05, 1.25 per 20-micron increase in caliber), but the caliber of retinal arterioles was not associated with stroke (pooled hazard ratio = 1.00, 95% confidence interval: 0.92, 1.08). There was weak evidence of heterogeneity in the hazard ratio for retinal venular caliber, which may be attributable to differences in follow-up strategies across studies. Inclusion of retinal venular caliber in prediction models containing traditional stroke risk factors reassigned 10.1% of people at intermediate risk into different, mostly lower, risk categories.

Retinal vascular fractal dimension and risk of early diabetic retinopathy: A prospective study of children and adolescents with type 1 diabetes

OBJECTIVE

To examine the prospective association of retinal vascular fractal dimension with diabetic retinopathy risk in young people with type 1 diabetes.

RESEARCH DESIGN AND METHODS

This was a hospital-based prospective study of 590 patients aged 12-20 years with type 1 diabetes free of retinopathy at baseline. All patients had seven-field retinal photographs taken of both eyes. Incident retinopathy was ascertained from retinal photographs taken at follow-up visits. Fractal dimension was measured from baseline photographs using a computer-based program following a standardized protocol.

RESULTS

Over a mean +/- SD follow-up period of 2.9 +/- 2.0 years, 262 participants developed mild nonproliferative diabetic retinopathy (15.0 per 100 person-years). After adjusting for age, sex, diabetes duration, A1C, and other risk factors, we found no association between retinal vascular fractal dimension and incident retinopathy.

CONCLUSIONS

Retinal vascular fractal dimension was not associated with incident early diabetic retinopathy in this sample of children and adolescents with type 1 diabetes.

Retinal vascular caliber and extracranial carotid disease in patients with acute ischemic stroke: the Multi-Centre Retinal Stroke (MCRS) study

BACKGROUND AND PURPOSE

Previous studies show that both retinal vascular caliber and carotid disease predict incident stroke in the general population, but the exact relationship between these 2 microvascular and macrovascular structural risk factors is unclear. We studied the relationship between retinal vascular caliber and carotid disease in patients presenting with acute ischemic stroke.

METHODS

We conducted a cross-sectional study of patients with acute ischemic stroke recruited from 3 centers (Melbourne, Sydney, Singapore). The caliber of retinal arterioles and venules was measured from digital retinal photographs. Severe extracranial carotid disease was defined as stenosis >or=75% or occlusion determined by carotid Doppler using North American Symptomatic Carotid Endarterectomy Trial-based criteria.

RESULTS

Among the 1029 patients with acute stroke studied, 7% of the population had severe extracranial carotid disease. Retinal venular caliber was associated with ipsilateral severe carotid disease (P<0.001 in multivariate models). Patients with wider retinal venular caliber were more likely to have severe ipsilateral carotid disease (multivariable-adjusted OR, 3.81; 95% CI, 1.80 to 8.07, comparing the largest and smallest venular caliber quartiles). The retinal venular caliber-carotid disease association remained significant in patients with large artery stroke.

CONCLUSIONS

In patients with acute stroke, retinal venular widening was strongly associated with ipsilateral severe extracranial carotid disease. Our findings suggest concomitant retinal and cerebral microvascular disease may be present in patients with carotid stenosis or occlusion disease. The pathogenesis of stroke due to carotid disease may thus be partially mediated by microvascular disease.

Meta-analysis: retinal vessel caliber and risk for coronary heart disease

BACKGROUND

Retinal vessel caliber may be a novel marker of coronary heart disease (CHD) risk. However, the sex-specific effect, magnitude of association, and effect independent of traditional CHD disease risk factors remain unclear.

PURPOSE

To determine the association between retinal vessel caliber and risk for CHD.

DATA SOURCES

Relevant studies in any language identified through MEDLINE (1950 to June 2009) and EMBASE (1950 to June 2009) databases.

STUDY SELECTION

Studies were included if they examined a general population, measured retinal vessel caliber from retinal photographs, and documented CHD risk factors and incident CHD events.

DATA EXTRACTION

6 population-based prospective cohort studies provided data for individual participant meta-analysis.

DATA SYNTHESIS

Proportional hazards models, adjusted for traditional CHD risk factors, were constructed for retinal vessel caliber and incident CHD in women and men. Among 22,159 participants who were free of CHD and followed for 5 to 14 years, 2219 (10.0%) incident CHD events occurred. Retinal vessel caliber changes (wider venules and narrower arterioles) were each associated with an increased risk for CHD in women (pooled multivariable-adjusted hazard ratios, 1.16 [95% CI, 1.06 to 1.26] per 20-microm increase in venular caliber and 1.17 [CI, 1.07 to 1.28] per 20-microm decrease in arteriolar caliber) but not in men (1.02 [CI, 0.94 to 1.10] per 20-microm increase in venular caliber and 1.02 [CI, 0.95 to 1.10] per 20-microm decrease in arteriolar caliber). Women without hypertension or diabetes had higher hazard ratios.

LIMITATION

Error in the measurement of retinal vessel caliber and Framingham variables was not taken into account.

CONCLUSION

Retinal vessel caliber changes were independently associated with an increased risk for CHD events in women.

Retinal microvascular signs and cognitive impairment

OBJECTIVES

To examine the association between retinal microvascular signs, as a proxy for cerebral microvascular disease, and cognitive impairment.

DESIGN

Cross-sectional population-based study.

SETTING

Urban population survey

PARTICIPANTS

One thousand nine hundred eighty-eight persons aged 49 to 97.

MEASUREMENTS

All participants underwent retinal photography and had the Mini-Mental State Examination (MMSE) administered by trained personnel. Retinal photographs were masked and graded for retinopathy signs (microaneurysms, hemorrhages, hard exudates, cotton wool spots), and retinal vessel calibers were measured using a validated computer-assisted method. Cognitive impairment was defined as an MMSE score of 23 or less, in line with other epidemiological studies.

RESULTS

Cognitive impairment was present in 121 participants (6.1%). In the total population, after adjusting for age, sex, blood pressure, diabetes mellitus, smoking, cardiovascular disease, education, and other factors, retinal venular dilation was associated with cognitive impairment (odds ratio (OR)=1.8, 95% confidence interval (95% CI)=1.0-3.2, P=.03). In persons with hypertension, retinopathy signs (adjusted OR=1.7, 95% CI=1.0-3.2, P=.05) and retinal venular dilation (adjusted OR=2.7, 95% CI=1.2-6.1, P=.01) were associated with cognitive impairment.

CONCLUSION

Retinal microvascular signs are associated with significant cognitive impairment, particularly in older persons with hypertension. These findings suggest that cerebral microvascular changes may contribute to cognitive deterioration.

Relationship between glycated haemoglobin and microvascular complications: is there a natural cut-off point for the diagnosis of diabetes?

AIMS/HYPOTHESIS

This study was designed to determine whether the relationship of glycated haemoglobin to diabetic microvascular complications shows any natural thresholds that could be useful in diagnosing diabetes.

METHODS

We examined a population-based sample of 3,190 Malay adults aged 40-80 years in Singapore. The microvascular outcomes of interest were: (1) any retinopathy, defined from fundus photographs; (2) mild retinopathy, defined as in (1); (3) moderate retinopathy, defined as in (1); (4) chronic kidney disease, defined from estimated glomerular filtration rate; (5) micro- or macroalbuminuria, defined from urinary albumin to creatinine ratio; and (6) peripheral neuropathy, defined from neurothesiometer or monofilament sensory testing.

RESULTS

Increasing HbA(1c) was associated with all microvascular complications. The optimal cut-off points for detecting mild and moderate retinopathy were 6.6% (87.0% sensitivity, 77.1% specificity and area under the receiver operating characteristics [ROC] curve 0.899) and 7.0% (82.9% sensitivity, 82.3% specificity and area under ROC curve 0.904). The prevalences of mild and moderate retinopathy were <1% below the optimal cut-off points. For other complications, the association with HbA(1c) was linear without evidence of a distinct threshold. Although ROC analysis for these other complications also suggested optimal cut-off points between 6.6% and 7.0%, the sensitivity at these cut-off points was considerably lower than for mild and moderate retinopathy, ranging from 31.8% to 66.5%.

CONCLUSIONS/INTERPRETATION

Higher levels of HbA(1c) were associated with microvascular complications. Our data support use of an HbA(1c) cut-off point of between 6.6 and 7.0% in diagnosing diabetes. Cut-off points in this range were best for the identification of individuals with mild and moderate retinopathy. Any retinopathy, chronic kidney disease, albuminuria and peripheral neuropathy are less well detected at these cut-off points.