By Allison Young, MD

Diabetic Macular Edema –

Now the most common cause of vision impairment in patients with diabetes

By Allison Young, MD

Diabetes has been steadily rising in the United States over the past several decades. According to data from the CDC, 37.3 million Americans have diabetes. This accounts for 11.3% of the population. An additional 96 million people have prediabetes. These staggering numbers result in incredible cost, both directly in medical cost and indirectly in lost productivity. In 2017, this cost totaled $327 billion.

Of those with diabetes, about 20-30% have diabetic retinopathy. In the past, the most common cause of vision loss in patients with diabetic retinopathy was proliferative diabetic retinopathy. Today, vision impairment in diabetics is most caused by diabetic macular edema, which is present in 3.8% of patients with diabetes.

Diabetic macular edema (DME) is diagnosed on clinical exam and retinal imaging such as OCT (optical coherence tomography). OCT imaging allows earlier recognition of macular edema and has become the standard for screening, diagnosis and monitoring of treatment response. The hallmark findings of DME are hard exudates and intraretinal edema. In poorly controlled diabetics, the retina becomes ischemic due to microvascular obstruction and retinal capillary dropout. The resultant hypoxia drives upregulation of vascular endothelial growth factor (VEGF), leading to neovascularization in the retinal periphery and in the vessels in the macula. These changes increase vascular permeability, allowing lipid and fluid to extravasate. In addition to the VEGFdriven changes, patients with diabetes often experience inflammatory cascades as well. The production of free radicals upregulates pro-inflammatory cytokines, which further damages the microvasculature.

The treatment of DME has undergone an incredible evolution over the past several decades. In the 1980s, laser photocoagulation became the standard of care for DME treatment. Argon laser treatments were applied in either focal treatment to the retinal microaneurysms or a grid pattern. Vision loss in DME patients was decreased by 50% at 3 years. However, vision improved in only 3% of patients due to the destructive nature of the treatment. Today, primary focal laser is only considered in cases with microaneurysms outside of the fovea (the center of the macula).

Currently, the mainstay of treatment is the injection of anti-VEGF drugs directly into the vitreous through the pars plana, the flat posterior portion of the ciliary body. Initially, injections were required every 4 weeks. In recent years, longer-acting drugs have become available, sometimes allowing treatments to be spaced to 8 or 12 weeks. All antiVEGF treatments result in superior visual gains compared to laser photocoagulation.

Unfortunately, anti-VEGF therapy is unsuccessful in about 40% of patients with chronic DME. In these patients, inflammation may be the primary cause of the underlying microvascular changes. Therefore, intravitreal corticosteroids are often utilized in these cases. Steroid treatments may be given in singular injections or delivered via sustained-release intravitreal implants. Complications of intravitreal steroids include increased intraocular pressure and rapid cataract progression, often requiring surgery.

In cases that are refractory to the above treatments, micropulse laser may be considered. Micropulse laser uses longer wavelengths of laser at shorter pulses. The shorter and less intense laser exposure selectively targets the retinal pigment epithelium (at the base of the retina) and spares the neurosensory retina, thereby preserving retinal function and decreasing the risk of hemorrhage and thermal damage.

Diabetic macular edema is often challenging to treat, making it frustrating for both the treating physician and the patient. Fortunately, treatment options continue to improve in both efficacy and duration of treatment, because DME may be asymptomatic early in its course, it is imperative that diabetics be screened regularly for this ocular manifestation. All Type 2 diabetics should be seen by an ophthalmologist at least annually, with frequency intervals tailored to the patients based on the severity of diabetic retinopathy.

References 1. By the Numbers: Diabetes in America. (2022). CDC. https://www.cdc.gov/diabetes/health-equity/diabetes-by-thenumbers.html 2. Diabetic Macular Edema: Diagnosis and Management. (2021, October 30). American Academy of Ophthalmology. https://www.aao.org/eyenet/article/diabetic-macular-edema-diagnosis-and-management?may-2021 3. Barash, A., Feistmann, J., & Gentile, R. (2017, October 1). The Role of Laser in Diabetic Macular Edema. Retinal Physician. https://www.retinalphysician.com/issues/2017/october-2017/therole-of-laser-in-diabetic-macular-edema

Allison Young, MD is a board-certified ophthalmologist in private practice at Stone Oak Ophthalmology. She is the Presidentelect of the San Antonio Society of Ophthalmology and a member of the Bexar County Medical Society.