Retinal vascular changes in pre-diabetes and prehypertension: new findings and their research and clinical implications

Adolescents with Type 2 diabetes: early indications of focal retinal neuropathy, retinal thinning, and venular dilation

PURPOSE

The eye provides a unique window into the neural and vascular health of a patient with diabetes. The present study is the first of its kind to examine the neural retinal function, structure, and retinal vascular health in adolescents with Type 2 diabetes.

METHODS

Focal neural responses from 103 discrete retinal regions of the eye were tested using multifocal electroretinography. Optical coherence tomography was utilized to measure retinal thickness. Digital fundus photographs were examined for the presence of retinopathy and to measure vascular caliber using retinal vessel analysis. Fifteen adolescents diagnosed with Type 2 diabetes, aged 13 to 21 years with a mean diabetes duration of 2.1 +/- 1.3 years, were tested. Twenty-six age-matched control subjects were also tested.

RESULTS

Multifocal electroretinograms of the Type 2 diabetic group were significantly (P = 0.03) delayed by 0.49 milliseconds. The diabetic group also showed significant (both; P < or = 0.03) retinal thinning (10.3 microm) and significant venular dilation (16.2 microm).

CONCLUSION

The present study shows early indications of focal retinal neuropathy, retinal thinning, and venular dilation in adolescents with Type 2 diabetes. Early detection of functional and structural changes will hopefully aid in the prevention of permanent damage or further functional loss.

Retinal microvascularisation abnormalities and cardiovascular risk

The progress of retinal imaging techniques has made retinal microvascular circulation easier to study. A number of observational studies were conducted to characterise the different abnormalities encountered and to determine the factors contributing to their onset. Three lesion groups were highlighted, including reduced arteriolar diameter, venular dilatation and retinopathy lesions. Retinal arteriolar narrowing signals the presence of hypertension (current or old) and the risk of hypertension onset. A genetic factor was implicated in this relationship. Venular dilatation and retinopathy correlate with the presence of diabetes, obesity and metabolic disorders. This association appears to be mediated partly by the presence of endothelial dysfunction and inflammation. The relationship between these abnormalities and cardiovascular risk was also studied in a number of longitudinal studies: the presence of retinal microvascular abnormalities is related with an increased risk of cardiovascular morbidity and mortality predominantly in individuals under the age of 75. More specifically, retinopathy is correlated with the presence of cerebral white matter lesions detected by MRI, an increased stroke risk and deterioration in cognitive function. On the cardiovascular level, a correlation was demonstrated between diminished coronary reserve, increased coronary calcifications observed by CT scan, coronary morbidity and mortality, and risk of heart failure. New techniques of retinal imaging, such as laser Doppler flowmetry, are still undergoing assessment and will help further to clarify these correlations.

Quantitative assessment of early diabetic retinopathy using fractal analysis

OBJECTIVE

Fractal analysis can quantify the geometric complexity of the retinal vascular branching pattern and may therefore offer a new method to quantify early diabetic microvascular damage. In this study, we examined the relationship between retinal fractal dimension and retinopathy in young individuals with type 1 diabetes.

RESEARCH DESIGN AND METHODS

We conducted a cross-sectional study of 729 patients with type 1 diabetes (aged 12-20 years) who had seven-field stereoscopic retinal photographs taken of both eyes. From these photographs, retinopathy was graded according to the modified Airlie House classification, and fractal dimension was quantified using a computer-based program following a standardized protocol.

RESULTS

In this study, 137 patients (18.8%) had diabetic retinopathy signs; of these, 105 had mild retinopathy. Median (interquartile range) retinal fractal dimension was 1.46214 (1.45023-1.47217). After adjustment for age, sex, diabetes duration, A1C, blood pressure, and total cholesterol, increasing retinal vascular fractal dimension was significantly associated with increasing odds of retinopathy (odds ratio 3.92 [95% CI 2.02-7.61] for fourth versus first quartile of fractal dimension). In multivariate analysis, each 0.01 increase in retinal vascular fractal dimension was associated with a nearly 40% increased odds of retinopathy (1.37 [1.21-1.56]). This association remained after additional adjustment for retinal vascular caliber.

CONCLUSIONS

Greater retinal fractal dimension, representing increased geometric complexity of the retinal vasculature, is independently associated with early diabetic retinopathy signs in type 1 diabetes. Fractal analysis of fundus photographs may allow quantitative measurement of early diabetic microvascular damage.

Population-based studies in ophthalmology

PURPOSE

To review major findings of population-based studies in ophthalmology, to summarize key questions, and to highlight future directions for this study design.

DESIGN

Summary and critical analysis of major population-based studies in eye diseases.

METHODS

Literature review and interpretation.

RESULTS

In the last 30 years, there have been many population-based studies in ophthalmology conducted in the United States and other countries around the world. These studies have provided information on the epidemiology of visual loss and the major eye diseases associated with visual loss; the risk factors; and the socioeconomic burden of eye disease. Population-based studies remain the most valid to determine the prevalence and incidence of a disease, and the population-attributable risk of new risk factors, including the interaction of genetic markers with systemic and environmental factors. Repeated surveys over time may also demonstrate impact of preventive strategies.

CONCLUSIONS

Population-based studies have provided substantial data on the frequency and impact of the major eye diseases in the community. This study design will continue to have an important role in addressing key questions of why eye diseases occur, who is at highest risk, and what preventive and therapeutic strategies are necessary to eliminate these diseases.

Treating prehypertension: a review of the evidence

Although the term "prehypertension" has been challenged by some, its use to define people with systolic blood pressure (BP) between 120 and 139 mm Hg and/or diastolic pressures between 80 and 89 mm Hg has gained general acceptance. The category includes as many people as the number who have hypertension, defined as blood pressure of 140/90 or above. Such people are clearly at an increased risk of cardiovascular damage compared with people with BPs below 120/80 mm Hg. The major unresolved issue is the appropriate management of such patients. Two trials have attempted to document the value of short-term drug therapy to prevent the progression of BP to overt hypertension, but no outcome studies are currently available.

A new look at screening and diagnosing diabetes mellitus

OBJECTIVE

Diabetes is underdiagnosed. About one third of people with diabetes do not know they have it, and the average lag between onset and diagnosis is 7 yr. This report reconsiders the criteria for diagnosing diabetes and recommends screening criteria to make case finding easier for clinicians and patients.

PARTICIPANTS

R.M.B. invited experts in the area of diagnosis, monitoring, and management of diabetes to form a panel to review the literature and develop consensus regarding the screening and diagnosis of diabetes with particular reference to the use of hemoglobin A1c (HbA1c). Participants met in open session and by E-mail thereafter. Metrika, Inc. sponsored the meeting.

EVIDENCE

A literature search was performed using standard search engines.

CONSENSUS PROCESS

The panel heard each member's discussion of the issues, reviewing evidence prior to drafting conclusions. Principal conclusions were agreed on, and then specific cut points were discussed in an iterative consensus process.

CONCLUSIONS

The main factors in support of using HbA1c as a screening and diagnostic test include: 1) HbA1c does not require patients to be fasting; 2) HbA1c reflects longer-term glycemia than does plasma glucose; 3) HbA1c laboratory methods are now well standardized and reliable; and 4) errors caused by nonglycemic factors affecting HbA1c such as hemoglobinopathies are infrequent and can be minimized by confirming the diagnosis of diabetes with a plasma glucose (PG)-specific test. Specific recommendations include: 1) screening standards should be established that prompt further testing and closer follow-up, including fasting PG of 100 mg/dl or greater, random PG of 130 mg/dl or greater, or HbA1c greater than 6.0%; 2) HbA1c of 6.5-6.9% or greater, confirmed by a PG-specific test (fasting plasma glucose or oral glucose tolerance test), should establish the diagnosis of diabetes; and 3) HbA1c of 7% or greater, confirmed by another HbA1c- or a PG-specific test (fasting plasma glucose or oral glucose tolerance test) should establish the diagnosis of diabetes. The recommendations are offered for consideration of the clinical community and interested associations and societies.

Relationship of retinal vascular caliber with diabetes and retinopathy: the Multi-Ethnic Study of Atherosclerosis (MESA)

OBJECTIVE

To examine the relationship of retinal vascular caliber with diabetes, glycemia, and diabetic retinopathy.

RESEARCH DESIGN AND METHODS

Population-based study using data from the Multi-Ethnic Study of Atherosclerosis (MESA), comprising 5,976 individuals (whites, blacks, Hispanics, and Chinese) residing in six U.S. communities who were free of clinical cardiovascular disease at baseline. Retinal vascular caliber was measured from digital retinal photographs.

RESULTS

There were 4,585 individuals with normal fasting glucose (NFG), 499 with impaired fasting glucose (IFG), 165 with diabetes with retinopathy signs, and 727 with diabetes without retinopathy signs. After multivariate analysis, retinal arteriolar caliber increased from 143.8 microm in subjects with NFG to 144.5 microm in IFG and 146.1 microm in diabetes (P < 0.001 for trend). Retinal venular caliber increased from 214.4 microm in NFG to 216.7 microm in IFG and 218.0 microm in diabetes (P < 0.001 for trend). Retinal venular caliber was significantly larger with increasing levels of fasting glucose and A1C. In a subgroup analysis by ethnicity, the association between wider arteriolar caliber and diabetes was evident in whites only, whereas wider venular caliber and diabetes was evident in Hispanics and Chinese only. In people with diabetes, eyes with retinopathy had larger retinal venular but not arteriolar caliber.

CONCLUSIONS

Retinal arteriolar and venular calibers are larger in individuals with diabetes, but the pattern of associations appears to vary by ethnicity. Retinal venular caliber is additionally associated with retinopathy signs. These findings add further to the concept that variations in retinal vascular caliber may reflect early diabetic microvascular damage.

Retinal arteriolar narrowing predicts incidence of diabetes: the Australian Diabetes, Obesity and Lifestyle (AusDiab) Study

OBJECTIVE

To examine the relationship of retinal vascular caliber to incident diabetes in a population-based cohort.

RESEARCH DESIGN AND METHODS

The Australian Diabetes, Obesity and Lifestyle (AusDiab) Study recruited adults aged 25+ years across Australia in 1999-2000, with a follow-up 5 years later in 2004-2005. Participants' glycemic status was classified using fasting plasma glucose (FPG) and 2-h oral glucose tolerance (2-h plasma glucose [2hPG]) tests. Diabetes was diagnosed if FPG was >or=7.0 mmol/l or 2hPG was >or=11.1 mmol/l. Retinal vascular caliber was measured from baseline retinal photographs using a computer-assisted program.

RESULTS

Of the 803 participants without diabetes at baseline, 108 (13.4%) developed diabetes at follow-up: 7 (2.8%) of 246 participants with normal glucose tolerance, 9 (13.6%) of 66 participants with impaired fasting glucose, and 92 (18.7%) of 491 participants with impaired glucose tolerance. After multivariate analysis, participants with narrower retinal arteriolar caliber had a higher risk of diabetes (odds ratio 2.21 [95% CI 1.02-4.80], comparing smallest versus highest arteriolar caliber tertiles, P = 0.04 for trend). There was no association between retinal venular caliber and incident diabetes.

CONCLUSIONS

Narrower retinal arteriolar caliber predicted risk of diabetes. These data provide further evidence that microvascular changes may contribute to the pathogenesis of diabetes.