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    New strategies to assess the risk of diabetes-related vision loss

    ODs must go outside the lines of traditional eye care

     

    Minimizing risk

    Once a diabetes diagnosis has been established, our goal shifts from helping patients prevent diabetes to helping them minimize the risk of developing diabetic retinopathy in general and STR in particular.

    We know that lower mean blood glucose as reflected by hemoglobin A1c (HbA1c) reduces DR incidence and progression, but it must be balanced against higher risks of tight control in some populations (preexisting cardiovascular disease, younger children, elderly, poor cognition, hypoglycemia unawareness, short life expectancy).27

    Interestingly, mean HbA1c during the DCCT accounted for a mere 6 to 11 percent of variance in DR during the 10-year trial, suggesting that other aspects of blood glucose may confer greater risk (e.g., short-term spikes too brief to be captured by HbA1c but severe enough to initiate and sustain a biochemical cascade of retinal injury).28

    It is helpful to counsel patients about individually appropriate blood glucose targets in coordination with the diabetes physician (see Table 2).

    Many patients use insulin, including a significant number with type 2 diabetes, and I have learned through personal and professional experience to ask my patients about appropriate timing of insulin (prior to eating in the case of rapid-acting insulin like Novolog [lispro, NovoNordisk]) and the importance of rotating injection sites to minimize scarring (lipohypertrophy) that interferes with subcutaneous insulin absorption (see Figure 2).

    Newer evidence suggests that certain, common oral medicines may significantly reduce the risk of DR progression, including blood pressure drugs that block the renin-angiotensin-aldosterone system (RAAS) as well as the triglyceride-lowering agent, fenofibrate.29,30 I would encourage every optometrist to discuss this with patients who have mild to moderate non-proliferative diabetic retinopathy (NPDR).

    Related: Keeping up with the latest diabetic eye disease research

    A number of studies have shown that diabetes affects visual function (contrast and visual field sensitivity, color discrimination) before the onset of DR, and that these measures worsen as DR progresses.31-34 Low contrast acuity charts and contrast sensitivity gratings are widely available, as are color vision instruments particularly suited to detecting acquired blue-yellow and red-green deficits commonly seen in patients with DR/DME (ColorDx, Konan Medical; Rabin Cone Contrast Test, Innova Systems).

    ODs should consider routinely testing visual function in patients with diabetes and attempt remediation through improved metabolic control or nutritional supplementation.

    Studies suggest that AREDS formula nutrients slowed progression of DR in human subjects,35 and my own research—the Diabetes Visual Function Supplement Study (DiVFuSS)—showed that a novel, multi-component nutritional supplement containing lutein, zeaxanthin, antioxidants, and select botanical extracts significantly improved visual function in patients with both type 1 and type 2 diabetes, both with and without DR, and without affecting HbA1c in a randomized, placebo-controlled clinical trial.36

    The test formula also significantly reduced symptoms of diabetic neuropathy, LDL cholesterol, triglycerides, and the inflammatory serum marker, and high sensitivity C-reactive protein (hsCRP); in an animal model, the formula prevented DR (elevated VEGF, mitochondrial DNA damage, retinal pericyte death, and ERG abnormalities) without affecting blood glucose levels.37

    Diabetes damages the retina long before we can see the vascular lesions of DR with conventional examination techniques. Earlier detection of subclinical DR has now become possible with the advent of advanced imaging modalities, including adaptive optics and more available (and affordable) options like multi-spectral imaging (Annidis RHA; see Figure 1) and OCT angiography (AngioVue, Optovue; AngioPlex, Zeiss) that utilizes motion contrast imaging with sequential OCT B-scans to construct a map of blood flow within the retina, choroid and optic nerve microvasculature.38,39

    OCTA can show subclinical microaneurysm formation, abnormal capillary looping, and areas of reduced capillary density or non-perfusion that may precede development of ophthalmoscopically detectable lesions typically seen in early DR (see Figure 3). OCTA is quick and non-invasive. It may facilitate not only identification of higher-risk patients for more careful follow-up, but a new way to assess the efficacy of therapy to prevent DR progression.

    We have more tools than ever to combat the diabetes epidemic and prevent blindness. If current trends hold, we’re going to be seeing an increasing number of patients with diabetes and at substantial risk for vision loss. By going outside the lines in our evaluation, management, and education, we can preserve and enhance eyesight and deliver the care a majority of our patients now require.

    Related: Ocular manifestations of diabetes: Some clues for eyecare professionals

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