Diabetic Retinopathy

Diabetes mellitus (DM) is a worldwide pandemic that currently affects nearly 180 million people. An estimated 370 million are expected to be afflicted by this disease by 2030. Type I or juvenile diabetes accounts for 5% of the disease burden. The other 95% of diabetics have type II or adult onset diabetes, which accounts for the increasing prevalence of this disease due to the rise in obesity and sedentary life styles. DM primarily affects those older than 30 years of age. Moreover, DM is often silent early in the disease course. The United States Center for Disease Control and Prevention reports that an estimated 24 million Americans or 8% of the total US population have DM. One- third of these individuals is unaware that they have the disease. The prevalence of DM in the United States is expected to rise to 12% by the year 2025. If uncontrolled, the high level of blood sugar in people with DM, due to the inability to produce insulin (type I) or ineffectiveness of insulin (type II), leads to end organ damage, including retinal vascular damage known as retinopathy. This makes regular monitoring of blood sugar a universal must for people with this disease. Multiple clinical trials have shown that the level of blood sugar control is directly related to the severity of retinopathy and other end organ damage.^47-51 Other eye diseases that are more frequent in people with DM include glaucoma and cataracts.

The most feared complication from DM is vision loss, which is due to DR. In the United States, DR is the most common cause of blindness in the working age population (age 20-74) and currently affects over five million Americans. Nearly, 5% of these individuals have advanced DR that could lead to severe vision loss. As the population ages, by 2020, six million US residents will have DR and 1.34 million of these residents will have vision-threatening disease. DR rates in people 65 years of age or older are expected to quadruple by 2050, from 2.5 to 9.9 million.⁵² Epidemiologic studies have indicated that the rates of DR are present in 30%-40% of all populations of Americans 30 years of age and older. Nearly 90% of diabetics requiring insulin have some level of retinopathy after 10 years. Of those with DR for 15 years, including many over age 60, 10% are severely visually handicapped and 2% are legally blind.^53,54 Annually, 7200 persons become permanently blind from DR in the United States.⁵⁵ The National Federation of the Blind estimates that the average lifetime cost to society for each person who becomes blind is nearly $1 million.⁵⁶ Of course, the personal cost of going blind to an individual and their loved ones is immeasurable.

DR is a microvascular disease that has distinct stages. DR first develops as mild nonproliferative diabetic retinopathy (NPDR) with microaneurysms, and can progress to moderate and severe NPDR with time, poor glycemic control, and high blood pressure. Poor glycemic control leads to damage to vascular endothelial cells and loss of associated anatomic structures that support the integrity of capillaries. This results in poor microvascular circulation resulting in ischemia of retinal tissue. The ischemic retina releases VEGF, which increases tissue and vascular permeability allowing for retinal edema and hemorrhages. These changes lead to diabetic macular edema (DME), the major cause of vision loss in DR. VEGF also stimulates neovascularization. In this way, DR progresses to severe NPDR and then proliferative diabetic retinopathy (PDR). PDR can lead to vision loss by causing vitreous hemorrhage and tractional retinal detachments. Mild and moderate (NPDR) usually do not cause vision problems unless there is concurrent macular edema, which can occur at any stage. Severe NPDR may quickly progress to PDR over a few years in patients with poor glycemic control, which increases the risk of vision loss.

DR is often silent until it becomes severe and affects vision, at which time treatment by a retinal specialist is crucial to prevent severe visual handicap and/or permanent blindness. Treatments for DR include laser therapy and more recently intravitreal steroid or anti-VEGF injections (similar to

AMD), and/or surgery. Laser therapy has been a standard of care for over two decades for DME and PDR. It is often associated with local scotomas in areas of treated retina, but it has been shown to robustly limit vision loss in a majority of individuals.^57,58 Intravitreal steroids have been used for DME with improvement of vision in many patients. However, steroid-response glaucoma and cataract in phakic individuals may limit the use of steroids. For patients who can routinely keep followup appointments, intravitreal anti-VEGF agents are now the choice treatment for vision-threatening DR as studies have shown improved vision without risk of scotomas, cataract, or development of glaucoma in the short term.^59,60 Routine follow-up may be difficult for older adults due to transportation issues and other health issues that may be life threatening and require hospitalization.

Fortunately, tight regulation of blood sugar by regulating one’s diet, regular exercise, and adhering to appropriate medical therapy, along with regular dilated eye examinations by a trained eye care specialist can prevent vision loss even after many years of having DM. While diabetic patients must see their primary care provider at least yearly and often more frequently to obtain care and prescriptions necessary for survival, primary care providers are not trained or equipped to perform the required dilated retinal examination. Screening for DR with dilated retinal examinations is a specialized skill performed by eye care specialists and allows for appropriate treatment of vision- threatening DR with laser, intraocular medical therapy, and/or surgery to prevent permanent blindness. With the advent of increasingly affordable digital imaging technology, retinal imaging had become more accepted as an alternative to live screening in underserved populations. In addition, images of the retina serve as a tangible and real demonstration of the damage of elevated blood sugar levels on the body’s blood vessels as the eye is the only place in the body where one can nonin- vasively observe small blood vessels, such as capillaries, which are damaged in DM. These images are used by eye care providers to counsel diabetic patients on their risk of vision loss and thus can motivate patients to better control their blood sugar and systemic disease.⁶¹

Due to the importance of regular eye examinations in this population, the American Academy of Ophthalmology recommends yearly dilated eye examinations for all persons diagnosed with DM. Annual dilated eye examinations are also an important Healthcare Effectiveness Data and Information Set (HEDIS) criteria developed by the National Committee for Quality Assurance (NCQA) used by federal agencies and health insurance companies to measure the quality of care provided to the diabetic population. Furthermore, regular eye examinations are advocated for all adults, especially after the age of 30 to detect and timely treat vision-threatening conditions such as macular degeneration, glaucoma, cataract, and need for glasses.