Heritability of Retinal Vascular Fractals: A Twin Study.

Purpose: To determine the genetic contribution to the pattern of retinal vascular branching expressed by its fractal dimension. Methods: This was a cross-sectional study of 50 monozygotic and 49 dizygotic, same-sex twin pairs aged 20 to 46 years. In 50°, disc-centered fundus photographs, the retinal vascular fractal dimension was measured using the box-counting method and compared within monozygotic and dizygotic twin pairs using Pearson correlation coefficients. Falconer's formula and quantitative genetic models were used to determine the genetic component of variation. Results: The mean fractal dimension did not differ statistically significantly between monozygotic and dizygotic twin pairs (1.505 vs. 1.495, P = 0.06), supporting that the study population was suitable for quantitative analysis of heritability. The intrapair correlation was markedly higher (0.505, P = 0.0002) in monozygotic twins than in dizygotic twins (0.108, P = 0.46), corresponding to a heritability h2 for the fractal dimension of 0.79. In quantitative genetic models, dominant genetic effects explained 54% of the variation and 46% was individually environmentally determined. Conclusions: In young adult twins, the branching pattern of the retinal vessels demonstrated a higher structural similarity in monozygotic than in dizygotic twin pairs. The retinal vascular fractal dimension was mainly determined by genetic factors, which accounted for 54% of the variation. The genetically predetermination of the retinal vasculature may affect the retinal response to potential vascular disease in later life.

Noninvasive Retinal Markers in Diabetic Retinopathy: Advancing from Bench towards Bedside.

The retinal vascular system is the only part of the human body available for direct, in vivo inspection. Noninvasive retinal markers are important to identity patients in risk of sight-threatening diabetic retinopathy. Studies have correlated structural features like retinal vascular caliber and fractals with micro- and macrovascular dysfunction in diabetes. Likewise, the retinal metabolism can be evaluated by retinal oximetry, and higher retinal venular oxygen saturation has been demonstrated in patients with diabetic retinopathy. So far, most studies have been cross-sectional, but these can only disclose associations and are not able to separate cause from effect or to establish the predictive value of retinal vascular dysfunction with respect to long-term complications. Likewise, retinal markers have not been investigated as markers of treatment outcome in patients with proliferative diabetic retinopathy and diabetic macular edema. The Department of Ophthalmology at Odense University Hospital, Denmark, has a strong tradition of studying the retinal microvasculature in diabetic retinopathy. In the present paper, we demonstrate the importance of the retinal vasculature not only as predictors of long-term microvasculopathy but also as markers of treatment outcome in sight-threatening diabetic retinopathy in well-established population-based cohorts of patients with diabetes.

Inter-Eye Agreement in Measurement of Retinal Vascular Fractal Dimension in Patients with Type 1 Diabetes Mellitus.

PURPOSE: To investigate inter-eye agreement in retinal vascular fractal dimension (FD) in patients with type 1 diabetes. METHODS: In a cross-sectional study, both eyes were exained in 178 patients with type 1 diabetes. All vessels in a zone 0.5-2.0 disc diameters from the optic disc were traced and FD calculated with the box-counting method using SIVA-Fractal semiautomatic software. The modified Early Treatment Diabetic Retinopathy Study (ETDRS) scale was used to grade diabetic retinopathy (DR). Pitman's test of difference in variance was used to calculated inter-eye agreement in FD according to level of DR. RESULTS: Mean age and duration of diabetes was 37.0 years and 29.5 years, respectively, and 49.4% of participants were male. Mean FD of right and left eyes was 1.4540 and 1.4472, respectively. FD did not differ between eyes in patients with no or non-proliferative DR (NPDR) in both eyes. This was true for patients with the same level of DR in both eyes (n = 74, p = 0.73), as well as for patients in which the ETDRS level of DR between the eyes differed by 1 (n = 43, p = 0.99) or more (n = 9, p = 0.53). In patients treated for proliferative DR in one eye, FD was significantly lower in this eye compared to the other (n = 10, p = 0.03). CONCLUSION: FD did not differ significantly between the two eyes of patients with no DR or NPDR, despite differences in severity of DR.

Ophthalmic epidemiology in Europe: the "European Eye Epidemiology" (E3) consortium.

The European Eye Epidemiology (E3) consortium is a recently formed consortium of 29 groups from 12 European countries. It already comprises 21 population-based studies and 20 other studies (case-control, cases only, randomized trials), providing ophthalmological data on approximately 170,000 European participants. The aim of the consortium is to promote and sustain collaboration and sharing of data and knowledge in the field of ophthalmic epidemiology in Europe, with particular focus on the harmonization of methods for future research, estimation and projection of frequency and impact of visual outcomes in European populations (including temporal trends and European subregions), identification of risk factors and pathways for eye diseases (lifestyle, vascular and metabolic factors, genetics, epigenetics and biomarkers) and development and validation of prediction models for eye diseases. Coordinating these existing data will allow a detailed study of the risk factors and consequences of eye diseases and visual impairment, including study of international geographical variation which is not possible in individual studies. It is expected that collaborative work on these existing data will provide additional knowledge, despite the fact that the risk factors and the methods for collecting them differ somewhat among the participating studies. Most studies also include biobanks of various biological samples, which will enable identification of biomarkers to detect and predict occurrence and progression of eye diseases. This article outlines the rationale of the consortium, its design and presents a summary of the methodology.

Polymorphisms in the CTSH gene may influence the progression of diabetic retinopathy: a candidate-gene study in the Danish Cohort of Pediatric Diabetes 1987 (DCPD1987).

BACKGROUND: The incidence of type 1 diabetes mellitus (T1DM) is increasing globally, and as a consequence, more patients are affected by microvascular complications such as diabetic retinopathy (DR). The aim of this study was to elucidate possible associations between diabetes-related single-nucleotide polymorphisms (SNP) and the development of DR. METHODS: Three hundred and thirty-nine patients with T1DM from the Danish Cohort of Pediatric Diabetes 1987 (DCPD1987) went through an ophthalmic examination in 1995; 185 of these were reexamined in 2011. The development of DR was assessed by comparison of overall DR level between baseline and follow-up in the worst eye at baseline. Patients were graded on a modified version of the Early Treatment Diabetic Retinopathy Study (ETDRS) scale, and 20 SNPs were genotyped in 130 of the 185 patients. RESULTS: We found the CTSH/rs3825932 variant (C > T) was associated with reduced risk of progression to proliferative diabetic retinopathy (PDR) (OR [95 % CI] = 0.20 [0.07-0.56], p = 2.4 × 10(-3), padjust = 0.048) and ERBB3/rs2292239 variant (G > T) associated with increased risk of two-step progression (OR [95 % CI] = 2.76 [1.31-5.80], p = 7.5 × 10(-3), padjust = 0.15). The associations were independent of other known risk factors, such as HbA1c, sex, and diastolic blood pressure. CONCLUSION: In conclusion, CTSH/rs3825932 and ERBB3/rs2292239 SNPs were associated with reduced risk of progression to PDR and two-step progression of DR on the ETDRS scale accordingly. The variant CTSH remained statistically significant after adjusting for multiple testing. Our results suggest an overlap between genetic variants that confer risk of T1DM and progression of DR.

Early risk stratification in pediatric type 1 diabetes.

In the late 1980s all Danish children with type 1 diabetes were invited for a nationwide evaluation of glycemic control. Approximately 75% (n = 720) participated and have later been referred to as The Danish Cohort of Pediatric Diabetes 1987 (DCPD1987). The results were surprisingly poor glycemic control among these young patients which lead to a great emphasis on glycemic control in the Danish Pediatric Departments. In 1995 the participants were invited for yet another evaluation but this time with main focus on early signs of microvascular complications - 339 participated. The mean HbA1c had remained at high levels (9.6%) and 60% of the participants had some level of Diabetic Retinopathy (DR). However, as the patients with DR mostly had the very milder forms it was believed that stricter glycemic control would reverse or at least stop progression of the disease in accordance with results from the large intervention study DCCT. This was investigated further at follow-up in 2011. The first study in the present thesis aimed to describe the 16-year incidence, progression and regression of DR in 185 participants from the DCPD1987 cohort. The 16-year incidence of proliferative retinopathy (PDR), 2-step progression and regression of DR was 31.0, 64.4, and 0.0%, respectively. As expected, the participants with PDR at follow-up had significantly higher HbA1c-values at both baseline and follow-up than those without PDR. However; a significantly larger decrease in HbA1c was also observed in the group with PDR over the study period, which in accordance with DCCT should have prevented the development of PDR to some extent. A surprisingly high incidence of proliferative retinopathy amongst young patients with type 1 diabetes in Denmark was found despite improvements in HbA1c over time. The improvement in HbA1c was either too small or happened too late. This study highlights that sight-threatening diabetic retinopathy remain a major concern in type 1 diabetes and the importance of early glycemic control. Identifying high-risk patients at a very early stage is not only desired for prevention of diabetic retinopathy - neuropathy and nephropathy similarly remain frequent in type 1 diabetes. Early risk stratification will allow for timely implementation of effective interventions and for individualized screening and diabetes care. The second and third studies of this thesis provide the longest prospective studies to date on both retinal vessel calibers and retinal fractal dimensions and their predictive value on diabetic microvascular complications. Semi-automated computer software has been developed to measure smaller changes in the retinal vessels on retinal photographs. Two of the first parameters to be reliably estimated by these programs were retinal vessel calibers and retinal vascular fractal dimensions (a quantitative measure on vascular complexity). There is very limited knowledge on their predictive value on diabetic complications thus far. In the second and third study, a consistent relation between narrower retinal arteriolar calibers, wider retinal venular calibers, lower fractal dimensions and the 16-year incidences of diabetic neuropathy, nephropathy and proliferative retinopathy was found. This has never been shown before. The results on vessel analyzes provides indications of a common pathogenic pathway for diabetic microvascular complications and therefore a possibility of universal risk estimation for development of neuropathy, nephropathy and retinopathy in type 1 diabetes.

Comparison between Early Treatment Diabetic Retinopathy Study 7-field retinal photos and non-mydriatic, mydriatic and mydriatic steered widefield scanning laser ophthalmoscopy for assessment of diabetic retinopathy.

AIMS: To compare non-mydriatic, mydriatic and steered mydriatic widefield retinal images with mydriatic 7-field Early Treatment Diabetic Retinopathy Study (ETDRS)-standards in grading diabetic retinopathy (DR). METHODS: We examined 95 patients (190 eyes) with type 1 diabetes. A non-mydriatic, a mydriatic and four steered mydriatic 200° widefield retinal images were captured (Optos 200Tx, Optos plc, Dunfermline, Scotland) and compared to mydriatic 7-field 45° ETDRS images (Topcon 3D OCT-2000, Topcon, Tokyo, Japan). Images were graded for DR according to ETDRS-protocol by a trained and certified grader masked to the results of the corresponding grading. For agreement kappa-statistics were used. RESULTS: Exact level agreement with 7-field images was found in 76.3%, 76.1% and 70.7% for non-mydriatic, mydriatic and steered mydriatic widefield images, respectively. Corresponding values for one-level agreement were 99.0%, 98.9% and 99.5%, respectively. Non-mydriatic matched mydriatic widefield images almost fully with exact and one-level agreement of 96.8% and 100.0%, respectively. Mydriatic steered images resulted in higher grading in 24 eyes. CONCLUSIONS: Widefield images matched 7-field images favorably. Widefield images can be captured without pupil-dilation and only one image is needed. However, because of overlapping eyelashes and distortion some lesion might be missed. Mydriatic steered images in selected cases may solve some of these problems.

Retinal vascular fractals predict long-term microvascular complications in type 1 diabetes mellitus: the Danish Cohort of Pediatric Diabetes 1987 (DCPD1987).

AIMS/HYPOTHESIS: Fractal analysis of the retinal vasculature provides a global measure of the complexity and density of retinal vessels summarised as a single variable: the fractal dimension. We investigated fractal dimensions as long-term predictors of microvasculopathy in type 1 diabetes. METHODS: We included 180 patients with type 1 diabetes in a 16 year follow-up study. In baseline retinal photographs (from 1995), all vessels in a zone 0.5-2.0 disc diameters from the disc margin were traced using Singapore Institute Vessel Assessment-Fractal image analysis software. Artefacts were removed by a certified grader, and fractal dimensions were calculated using the box-counting method. At follow-up (in 2011), diabetic neuropathy, nephropathy and proliferative retinopathy were assessed and related to baseline fractal dimensions in multiple regressions adjusted for sex and baseline age, diabetes duration, HbA1c, BP, BMI, vibration perception threshold, albuminuria, retinopathy and vessel diameters. RESULTS: Mean baseline age and diabetes duration were 21.0 and 13.4 years, respectively, and of patients 50.0% were males. The mean fractal dimension was 1.3817. The 16 year incidences of neuropathy, nephropathy and proliferative retinopathy were 10.8%, 8.0% and 27.9%, respectively. Multiple regression analyses showed a lower fractal dimension to significantly predict incident neuropathy (OR 1.17 per 0.01 fractal dimension decrease [95% CI 1.01, 1.36]), nephropathy (OR 1.40 per 0.01 fractal dimension decrease [95% CI 1.10, 1.79]) and proliferative retinopathy (OR 1.22 per 0.01 fractal dimension decrease [95% CI 1.09, 1.37]). CONCLUSIONS/INTERPRETATION: The retinal vascular fractal dimension is a shared biomarker of diabetic microvasculopathy, thus indicating a possible common pathogenic pathway. Retinal fractal analysis therefore is a potential tool for risk stratification in type 1 diabetes.

Retinal vessel calibers predict long-term microvascular complications in type 1 diabetes: the Danish Cohort of Pediatric Diabetes 1987 (DCPD1987).

Diabetic neuropathy, nephropathy, and retinopathy cause significant morbidity in patients with type 1 diabetes, even though improvements in treatment modalities delay the appearance and reduce the severity of these complications. To prevent or further delay the onset, it is necessary to better understand common underlying pathogenesis and to discover preclinical biomarkers of these complications. Retinal vessel calibers have been associated with the presence of microvascular complications, but their long-term predictive value has only been sparsely investigated. We examined retinal vessel calibers as 16-year predictors of diabetic nephropathy, neuropathy, and proliferative retinopathy in a young population-based Danish cohort with type 1 diabetes. We used semiautomated computer software to analyze vessel diameters on baseline retinal photos. Calibers of all vessels coursing through a zone 0.5-1 disc diameter from the disc margin were measured and summarized as the central artery and vein equivalents. In multiple regression analyses, we found wider venular diameters and smaller arteriolar diameters were both predictive of the 16-year development of nephropathy, neuropathy, and proliferative retinopathy. Early retinal vessel caliber changes are seemingly early markers of microvascular processes, precede the development of microvascular complications, and are a potential noninvasive predictive test on future risk of diabetic retinopathy, neuropathy, and nephropathy.

The 16-year incidence, progression and regression of diabetic retinopathy in a young population-based Danish cohort with type 1 diabetes mellitus: The Danish cohort of pediatric diabetes 1987 (DCPD1987).

The aim was to investigate the long-term incidence of proliferative diabetic retinopathy (PDR), and progression and regression of diabetic retinopathy (DR) and associated risk factors in young Danish patients with Type 1 diabetes mellitus. In 1987-89, a pediatric cohort involving approximately 75 % of all children with Type 1 diabetes in Denmark <19 years of age was identified (n = 720). In 1995, 339 (47.1 %) were re-studied with retinopathy graded and all relevant diabetic parameters assessed. Of those, 185 (54.6 %) were evaluated again in 2011 for the same clinical parameters. All retinal images were graded using modified early treatment of DR study for 1995 and 2011. In 1995, mean age was 21.0 years and mean diabetes duration 13.5 years. The 16-year incidence of proliferative retinopathy, 2-step progression and 2-step regression of DR was 31.0, 64.4 and 0.0 %, respectively, while the incidence of DR was 95.1 %. In a multivariate logistic regression model, progression to PDR was significantly associated with 1995 HbA1c (OR 2.61 per 1 % increase, 95 % CI 1.85-3.68) and 1995 diastolic blood pressure (OR 1.79 per 10 mmHg increase, 95 % CI 1.04-3.07). Two-step progression of DR was associated with male gender (OR 2.37 vs. female, 95 % CI 1.07-5.27), 1995 HbA1c (OR 3.02 per 1 % increase, 95 % CI 2.04-4.48) and 1995 vibration perception threshold (OR 1.19 per 1 Volt increase, 95 % CI 1.02-1.40). In conclusion, one in three progressed to PDR and two in three had 2-step progression despite young age and increased awareness of the importance of metabolic control. After 30 years duration of diabetes, the presence of DR is almost universal.