Quantitative assessment of early diabetic retinopathy using fractal analysis

Carbohydrate nutrition is associated with changes in the retinal vascular structure and branching pattern in children

BACKGROUND

Higher intake of carbohydrates and high-glycemic index (high-GI) diets could lead to small vessel dysfunction.

OBJECTIVES

We aimed to assess the associations between intakes of high-GI and high-glycemic load (high-GL) diets, carbohydrate, and the main carbohydrate-containing food groups and retinal microvascular changes in preadolescents.

DESIGN

Students aged 12 y (n = 2353) from a random cluster sample of 21 schools underwent detailed eye examinations. Retinal vessel caliber and fractal dimension were measured from digital retinal images. A validated semiquantitative food-frequency questionnaire was administered.

RESULTS

After multivariable adjustment, children who consumed soft drinks once or more per day had significantly narrower mean retinal arterioles (∼1.9 μm) than did those who never or rarely consumed soft drinks (P-trend = 0.03). When the highest to lowest tertiles of carbohydrate consumption were compared, girls had significantly narrower retinal arterioles (∼1.4 μm; P-trend = 0.03) and boys had wider venules (∼2.3 μm; P-trend = 0.02). In girls only, a higher-GI diet was associated with narrower retinal arterioles (0.98-μm narrowing of retinal arteriolar caliber per SD increase in GI, P = 0.01). Carbohydrate intake and a high-GL diet were associated with greater retinal fractal dimension in girls (highest compared with lowest tertiles: P-trend = 0.003 and 0.01, respectively).

CONCLUSIONS

Greater consumption of carbohydrates and soft drinks was associated with retinal arteriolar narrowing and venular widening. Because these microvascular signs have been shown to be markers of future cardiovascular disease risk, the presence of this risk factor in children could support the need for healthy dietary patterns that include lower consumption of high-GI foods and soft drinks.

Retinal vascular geometry in Asian persons with diabetes and retinopathy

PURPOSE

Our purpose was to examine the relationship of retinal vascular parameters with diabetes and retinopathy in an older Asian population.

METHODS

Retinal photographs from participants of a population-based survey of Asian Malay persons aged 40-80 years were analyzed. Specific retinal vascular parameters (tortuosity, branching angle, fractal dimension, and caliber) were measured using a semiautomated computer-based program. Diabetes was defined as random plasma glucose ≥ 11.1 mmol/liter, the use of diabetes medication, or physician-diagnosed diabetes. Retinopathy signs were graded from photographs using the modified Airlie House classification system.

RESULTS

A total of 2735 persons were included in the study. Persons with diabetes (n = 594) were more likely to have straighter (less tortuous) arterioles and wider arteriolar and venular caliber than those without diabetes (n = 2141). Among subjects with diabetes, those with retinopathy had wider venular caliber than those without retinopathy (211.3 versus 204.9 mm, p = .001). Among nondiabetic subjects, however, those with retinopathy had more tortuous venules than those without retinopathy [5.19(×10(4)) versus 4.27(×10(4)), p < .001].

CONCLUSIONS

Retinal vascular parameters varied by diabetes and retinopathy status in this older Asian cohort. Our findings suggest that subtle alterations in retinal vascular architecture are influenced by diabetes.

Retinal vascular calibre as a predictor of incidence and progression of diabetic retinopathy

Recent advances in retinal photographic imaging techniques have allowed objective and precise measurement of subtle vascular characteristics in the retina, including the retinal vessel calibre (diameter). Data from population-based and clinic-based studies show that changes in retinal calibre are associated with systemic vascular risk factors and might reflect early microcirculatory alterations in people with diabetes prior to the onset of clinically significant complications, such as diabetic retinopathy. Prospective studies suggest that in people with type 1 diabetes, wider retinal venules are associated with progression of mild to more severe levels of retinopathy, including proliferative retinopathy. Thus, studying retinal vascular calibre changes might offer the potential to improve our understanding of the early pathophysiological pathways of diabetic retinopathy, potentially allowing the development of novel therapies. Future research is still needed to assess the ability of retinal vessel calibre measures to provide clinically useful prognostic information that might add to risk prediction of diabetic retinopathy over and above the contribution from traditional risk factors, including glycaemic levels and the duration of diabetes.

How does hypertension affect your eyes?

Hypertension has profound effects on various parts of the eye. Classically, elevated blood pressure results in a series of retinal microvascular changes called hypertensive retinopathy, comprising of generalized and focal retinal arteriolar narrowing, arteriovenous nicking, retinal hemorrhages, microaneurysms and, in severe cases, optic disc and macular edema. Studies have shown that mild hypertensive retinopathy signs are common and seen in nearly 10% of the general adult non-diabetic population. Hypertensive retinopathy signs are associated with other indicators of end-organ damage (for example, left ventricular hypertrophy, renal impairment) and may be a risk marker of future clinical events, such as stroke, congestive heart failure and cardiovascular mortality. Furthermore, hypertension is one of the major risk factors for development and progression of diabetic retinopathy, and control of blood pressure has been shown in large clinical trials to prevent visual loss from diabetic retinopathy. In addition, several retinal diseases such as retinal vascular occlusion (artery and vein occlusion), retinal arteriolar emboli, macroaneurysm, ischemic optic neuropathy and age-related macular degeneration may also be related to hypertension; however, there is as yet no evidence that treatment of hypertension prevents vision loss from these conditions. In management of patients with hypertension, physicians should be aware of the full spectrum of the relationship of blood pressure and the eye.

Eye complications and markers of morbidity and mortality in long-term type 1 diabetes

The incidence of type 1 diabetes is rising all over the world. Furthermore, the increased life-expectancy of type 1 diabetic patients is likely to cause a higher number of diabetes-related micro- and macrovascular complications in the years to come. In order to examine the level of long-term complications in type 1 diabetes as well as potential markers of micro- and macroangiopathy, a population-based cohort of Danish type 1 diabetic patients was examined in order to achieve the following aims: 1. To evaluate diabetic retinopathy as a long-term marker of all-cause mortality in type 1 diabetes (Paper I). 2. To estimate the long-term incidence and associated risk factors of blindness (Paper II) and cataract surgery (Paper III) in type 1 diabetes. 3 To use retinal vascular analyses in order to investigate the associations of long-term micro- and macrovascular complications and retinal vascular diameters (Paper IV) and retinal fractals (Paper V) in type 1 diabetes. 4. To examine N-terminal pro brain natriuretic peptide (Paper VI) and osteoprotegerin (Paper VII) as non-invasive markers of micro- and macrovascular complications in type 1 diabetes. In Paper I it was a major finding that, despite a mean age of only 38.3 years at baseline, 44.7% of the patients died during the 25-year follow-up. Patients who had proliferative retinopathy as well as proteinuria at the baseline examination had a significantly higher mortality. For these, the 10-year survival was only 22.2%. As demonstrated in Paper II, blindness is an important issue in type 1 diabetes. The 25-year cumulative incidence of blindness was 7.5%. Glycaemic regulation and maculopathy at baseline were both identified as risk factors of blindness. Finally, mortality was higher in patients who went blind during the follow-up. Cataract surgery is quite common in type 1 diabetes. In Paper III a 25-year cumulative incidence of 20.8% was found. Adjusted for mortality, this was even higher (29.4%). As compared to patients without diabetes, cataract surgery takes place approximately 20 years earlier in type 1 diabetic patients. Age and maculopathy at baseline were both identified as predictors of cataract surgery. In Paper IV it was demonstrated that patients with retinal arteriolar narrowing were 2.17 and 3.17 times more likely to have nephropathy and macrovascular disease, respectively. This was an important finding that suggests that retinal fundus photos may be used in order to predict the risk of non-ophthalmological complications in type 1 diabetes. Retinal fractal analysis is another way to evaluate the vascular system of the retina. In Paper V we found associations between retinal fractal and microvascular - but not macrovascular--disease. For instance, patients with lower fractal dimensions were more likely to have proliferative retinopathy (OR 1.45, 95% CI 1.04-2.03) and neuropathy (OR 1.42, 95% CI 1.01-2.01). NT-proBNP is likely to be a future predictor of diabetes-related complications. In Paper VI higher levels of NT-proBNP were related to nephropathy (OR 5.03, 95% CI 1.77-14.25), neuropathy (OR 4.08, 95% CI 1.52-10.97) and macrovascular disease (OR 5.84, 95% CI 1.65-20.74). These associations should be confirmed in future prospective studies. As opposed to NT-proBNP, osteoprotegerin is less likely to be a predictor of either micro- or macrovascular disease in type 1 diabetes. As demonstrated in Paper VII, even though association between higher levels of OPG and nephropathy were found in an age- and sex-adjusted model (OR 2.54, 95% CI 1.09-5.90), this was no longer statistically significant when other factors were taken into account. Overall, it was demonstrated that various complications such as mortality, blindness and cataract surgery were high in type 1 diabetes. Furthermore, retinal arteriolar narrowing, decreased retinal fractals and plasma NT-proBNP were associated with various micro- and macrovascular complications. If confirmed by prospective studies, these modalities may be used in order to identify patients at risk of diabetes-related complications. This could, ultimately, lead to decreased mortality and morbidity in type 1 diabetic patients.

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 fractal dimension is increased in persons with diabetes but not impaired glucose metabolism: the Australian Diabetes, Obesity and Lifestyle (AusDiab) study

AIMS/HYPOTHESIS

The fractal dimension (D(f)) of the retinal vasculature is a global measure of its branching pattern complexity. We examined the relationship of retinal D(f) with diabetes.

METHODS

We conducted a cross-sectional study of 1,577 participants with diabetes and impaired glucose metabolism and normal controls from the population-based Australian Diabetes, Obesity and Lifestyle (AusDiab) study. Retinal D(f) was quantified from fundus photographs using a computer-based programme and diabetes status was determined by oral glucose tolerance test based on the WHO criteria.

RESULTS

After adjustment for age, sex and vascular risk factors, persons with higher retinal D(f) were more likely to have diabetes (OR 1.56; 95% CI 1.14-2.14, highest vs lowest fractal tertile). This relationship remained with further adjustment for retinal arteriolar calibre and presence of retinopathy (OR 1.64; 95% CI 1.19-2.27), and after excluding participants with retinopathy (OR 1.60; 95% CI 1.16-2.21). Retinal D (f) was not related to impaired glucose tolerance or impaired fasting glucose (OR 1.19; 95% CI 0.85-1.67).

CONCLUSIONS/INTERPRETATION

Individuals with diabetes, but not with impaired glucose metabolism, have greater retinal D(f), reflecting greater complexity of the retinal vasculature. Our findings suggest the presence of early microvascular changes in the retinal vasculature of persons with diabetes, even in the absence of overt retinopathy.

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.

Diabetic retinopathy

Diabetic retinopathy is a common and specific microvascular complication of diabetes, and remains the leading cause of preventable blindness in working-aged people. It is identified in a third of people with diabetes and associated with increased risk of life-threatening systemic vascular complications, including stroke, coronary heart disease, and heart failure. Optimum control of blood glucose, blood pressure, and possibly blood lipids remains the foundation for reduction of risk of retinopathy development and progression. Timely laser therapy is effective for preservation of sight in proliferative retinopathy and macular oedema, but its ability to reverse visual loss is poor. Vitrectomy surgery might occasionally be needed for advanced retinopathy. New therapies, such as intraocular injection of steroids and antivascular endothelial growth-factor agents, are less destructive to the retina than are older therapies, and could be useful in patients who respond poorly to conventional therapy. The outlook for future treatment modalities, such as inhibition of other angiogenic factors, regenerative therapy, and topical therapy, is promising.

Fractal analysis of retinal vessels suggests that a distinct vasculopathy causes lacunar stroke

OBJECTIVES

Lacunar strokes account for 25% of all ischemic strokes and may represent the cerebral manifestation of a systemic small vessel vasculopathy of unknown etiology. Altered retinal vessel fractal dimensions may act as a surrogate marker for diseased cerebral vessels. We used a cross-sectional study to investigate fractal properties of retinal vessels in lacunar stroke.

METHODS

We recruited patients presenting with lacunar stroke and patients with minor cortical stroke as controls. All patients were examined by a stroke expert and had MRI at presentation. Digital retinal photographs were taken of both eyes. Monofractal and multifractal analyses were performed with custom-written semiautomated software.

RESULTS

We recruited 183 patients. Seventeen were excluded owing to poor photographic quality, leaving 166 patients (86 with lacunar and 80 with cortical stroke). The mean age was 67.3 years (SD 11.5 years). The patients with lacunar stroke were younger but the prevalence of diabetes, hypertension, and white matter hyperintensities did not differ between the groups. The mean Dbox (monofractal dimension) was 1.42 (SD 0.02), the mean D0 (multifractal dimension) 1.67 (SD 0.03). With multivariate analysis, decreased Dbox and D0 (both representing decreased branching complexity) were associated with increasing age and lacunar stroke subtype after correcting for hypertension, diabetes, stroke severity, and white matter hyperintensity scores.

CONCLUSIONS

Lacunar stroke subtype and increasing age are associated with decreased fractal dimensions, suggesting a loss of branching complexity. Further studies should concentrate on longitudinal associations with other manifestations of cerebral small vessel disease.

Age-related rarefaction in the fractal dimension of retinal vessel

Previous work suggests a general reduction in complexity with aging, referred to as the aging-complexity theory. Fractal dimension (FD) of the vessels in the retina is a global measure of the complexity of the vasculature. However, earlier works did not find any correlation between aging and FD of the retinal vasculature, in contrast to the findings of reduced complexity in other parts of the body. The authors tested the hypothesis that reduced complexity develops with advancing age in the structure of the retinal vasculature. To overcome the limitations of earlier works, a three-dimensional representation of the vasculature, together with Fourier fractal dimension (FFD) techniques, was used. Based on the analysis of 748 retinal images taken of persons aged 49-89 years, we observed a significant decrease in the FFD with aging (p < 0.0001). These data provide evidence supporting rarefaction (i.e. reduction) of the retinal vasculature with aging, consistent with observations from other human organ systems.

Automated analysis of retinal vascular network connectivity

This paper describes an algorithm that forms a retinal vessel graph by analysing the potential connectivity of segmented retinal vessels. Self organizing feature maps (SOFMs) are used to model implicit cost functions for the junction geometry. The algorithm uses these cost functions to resolve the configuration of local sets of segment ends, thus determining the network connectivity. The system includes specialized algorithms to handle overlapping vessels. The algorithm is tested on junctions drawn from the public-domain DRIVE database.

Adolescent type 1 Diabetes Cardio-renal Intervention Trial (AdDIT)

BACKGROUND

The prognosis for young people diagnosed with diabetes during childhood remains poor and this is mainly related to the long-term risk of developing vascular complications.Microalbuminuria identifies subjects at risk for diabetic nephropathy (DN) and cardiovascular disease (CVD). It is often detected in adolescence but is rarely treated before the age of 18 years, as at the end of puberty albumin excretion may decline and in some subjects will return into the normal range. However, evidence indicates that subjects with both transient and persistent microalbuminuria have experienced renal damage during puberty and thus reno-protection to prevent long-term complications is warranted. In adults with diabetes and microalbuminuria, the use of angiotensin converting enzyme inhibitors (ACEI) and Statins is increasing, and in order to determine whether these agents are of value in the adolescent population a large randomized controlled clinical trial is needed.

METHODS/DESIGN

The Adolescent type 1 Diabetes cardio-renal Intervention Trial (AdDIT) is a multi-center, randomized, double-blind, placebo-controlled trial of ACEI and Statin therapy in adolescents with type 1 diabetes. 500 high-risk adolescents, defined on the basis of their albumin excretion, are randomized to receive either ACEI (Quinapril) or Statins (Atorvastatin) or combination therapy or placebo for 3-4 years. There will also be a parallel open observational study, based on the follow-up of 400 low-risk non-randomized adolescents. The major endpoint of the study is the change in albumin excretion; secondary endpoints include markers of CVD, renal function, retinopathy, quality of life combined with assessment of compliance and potential health economic benefits.

DISCUSSION

AdDIT will provide important data on the potential renal and cardiovascular protective effects of ACEI and Statins in high-risk adolescents. Long-term follow-up of the randomized subjects will provide direct evidence of disease outcomes, in addition to the data on early surrogate measures of DN and CVD. Follow-up of non-randomized low-risk subjects will determine the potential impact of intervention on DN and CVD. AdDIT will help to determine whether, in addition to encouraging young people to achieve good glycaemic control, pharmacological cardio-renal protection should also be implemented. EUDRACT NUMBER: 2007-001039-72

TRIAL REGISTRATION NUMBER

ISRCTN91419926.

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 changes and diabetic retinopathy

Recent studies support the concept that the retinal vasculature may provide a summary measure of lifetime exposure to the effects of hyperglycemia. Advances in retinal photographic techniques and in image analysis have allowed objective and precise in vivo measurement of retinal vascular changes. In particular, quantitative assessment of retinopathy signs and measurement of retinal vascular caliber have greatly increased our knowledge of early microcirculatory alterations in prediabetes, diabetes, and diabetic micro- and macrovascular complications. Data from recent population-based studies suggest that retinal arteriolar and venular caliber changes reflect different pathophysiologic processes. Retinal arteriolar narrowing, for example, is associated with risk of diabetes and coronary artery disease, whereas retinal venular widening is associated with development and progression of diabetic retinopathy and risk of stroke. Studying these changes offers the potential to improve our understanding of the early pathophysiologic pathways of diabetes development and its complications. Future research will assess the ability of retinal vascular imaging to provide clinically useful prognostic information for patients with diabetes.