Diabetes Mellitus occurs when the body is unable to use and/or store sugar properly, resulting in high blood sugar levels. Abnormal blood glucose especially affects the smallest blood vessels of the body, including those in the eyes, kidneys, and at the ends of the fingertips and toes (this leads to diabetic retinopathy, diabetic nephropathy, and diabetic neuropathy, respectively).
According to population studies, 40-45% of people with diabetes may have diabetic retinopathy. When elevated blood sugar levels damage the tiny blood vessels located in the retina, they can leak fluid, blood, and start causing new abnormal blood vessels to grow. This can also lead to scar tissue developing over time and cause symptoms such as floaters, blurriness, distortion, and in severe cases, blindness.
How diabetes affects the eye
Diabetes tends to affect the eyes in two ways:
- Diabetic retinopathy, including abnormal blood vessel growth and bleeding into the eye, as well as having inadequate blood flow/oxygen to the tissues of the retina
- Swelling in the central retinal tissue, also termed diabetic macular edema.
Diabetic retinopathy is a progressive disease. The earlier form of the disease is categorized as different stages of nonproliferative or background diabetic retinopathy (NPDR or BDR), which can eventually progress to the more dangerous proliferative diabetic retinopathy (PDR).
Nonproliferative diabetic retinopathy (NPDR) can be mild, moderate, severe, or very severe. At the early stage, high blood glucose levels damage the lining of the retinal blood vessels, causing these vessels to leak, bleed, and create pockets of swelling within the retina. The blood flow in certain areas of the retina is not normal, causing loss of the normal capillary structure. As this unhealthy retina becomes starved for nutrients and oxygen, it is unable to function well and can also create a driving force for the body to try to create new blood vessels. This can lead to PDR, which is more severe.
Proliferative diabetic retinopathy (PDR) is when the blood vessel damage and demand for oxygen from the tissue are so severe that the retina tries to grow new blood vessels to compensate (a process called neovascularization). The problem is that these are very abnormal, curly, and leaky blood vessels that are unstable and do not help the retina but tend to cause bigger problems. Sometimes these vessels will bleed into the vitreous cavity of the eye causing sudden vision loss and severe floaters. Other times the vessels grow into larger networks over time and create scar tissue that tends to contract and pull the retina off the back of the eye (like wallpaper being lifted off the wall), ultimately causing a tractional retinal detachment. Sometimes the abnormal blood vessels can grow in the front section of the eye which can cause high intraocular pressure known as neovascular glaucoma.
Diabetic Macular Edema
The leakage of fluid into the central retina area, known as the macula, is a more immediate and visually symptomatic problem that can happen at any stage of the disease. Diabetic macular edema (DME) is when swelling occurs in the most important part of the retina, causing central vision issues such as distortion, blurriness, and dullness. Exudates or yellowish-colored lipid remnants can develop as the leakage waxes and wanes. There can be immediate problems from the initial edema or long-lasting damage from the anatomy of the retinal layers being disrupted or poor blood supply.
Some symptoms of diabetic retinopathy include:
- Blurry vision
- Missing parts in the vision or "dark areas"
- Vision that changes from blurry to clear
- Color washing or fading
How is diabetic retinopathy diagnosed?
Early diabetic retinopathy is often not noticeable to patients with very mild or no symptoms. This is the most important time to learn about the risks of the disease as well as possible symptoms, as early detection offers patients the best chance at preserving optimal vision. All diabetic patients should have an eye exam with their ophthalmologist or a diabetic eye specialist at least once a year so that any changes to the retina can be observed and treated immediately. If diabetic retinopathy is detected, additional appointments may be required.
How is diabetic retinopathy treated?
Diabetic retinopathy can be treated in several ways depending on the severity and location of the problem. As noted in many other circumstances, prevention is key, especially in the long-term implications of glucose control. This should ensure the long-term health of your vision. Patients with diabetes should carefully monitor their blood sugar and blood pressure, follow a healthy diet, and exercise regularly as advised by their doctor. These steps will reduce your risk of developing diabetic retinopathy.
Medications that go after the Vascular Endothelial Growth Factor (anti-VEGF medications) within the eye are a great treatment strategy to reduce the swelling within the retina and also decrease the drive for the eye to make new abnormal blood vessels. These medications are injected through the white part of the eye (scleral) into the internal vitreous cavity with a tiny needle; this delivers the anti-VEGF directly to the site. This is performed in-office with local or topical anesthesia.
Laser photocoagulation can be used in multiple ways to address the problems associated with diabetic retinopathy and macular edema. Laser is light-energy that can be used to help seal off leaking blood vessels and reduce swelling within the retina. Laser surgery can also be performed on the unhealthy part of the peripheral retina to help protect the central retina in a process called pan-retinal photocoagulation (PRP). This can decrease the rate of blood vessel growth. This treatment is normally performed in-office with topical anesthesia.
In more severe cases of proliferative diabetic retinopathy or if there is bleeding into the eye or a tractional retinal detachment present, vitrectomy surgery may be necessary. During this procedure, blood is removed from within the central cavity of the eye and any abnormal blood vessels are treated. Contracted scar tissue is removed from the back of the eye using small forceps and careful segmentation of these scarring areas may be needed to allow the retina to return to its normal position. Laser photocoagulation is used to treat the retina during this procedure to help seal the vessels, treat the abnormal non-vascularized retina, and create a PRP laser pattern to reduce future risk of bleeding. Of note for vitreous hemorrhage, often a waiting period is recommended before surgery to see if the blood will clear on its own, even if vision is impaired.