Diabetes is a long-term systemic condition that affects how the body manages blood sugar, leading to damage in many organs, including the eyes. The eye is particularly vulnerable because it relies on a network of extremely fine blood vessels to nourish the light-sensing tissue called the retina. When diabetes is not controlled, this delicate vascular system can be compromised, leading to severe vision problems. Eye injections are necessary because they are specifically designed to halt the progression of diabetic eye disease and preserve sight. This targeted drug delivery addresses the internal damage caused by chronic high glucose levels.
How High Blood Sugar Leads to Retinal Damage
Chronic high blood glucose levels systematically damage the small blood vessels, or microvasculature, that supply the retina. This damage is known as diabetic retinopathy. The early stage, non-proliferative diabetic retinopathy (NPDR), involves the vessel walls weakening, causing them to bulge and develop tiny pouches called microaneurysms. These microaneurysms can begin to leak fluid and blood into the retina.
As the condition progresses, the damaged vessels become blocked, which starves parts of the retina of oxygen and nutrients, a state called ischemia. In response to this oxygen deprivation, the retina releases chemical signals that trigger the growth of new blood vessels. This advanced stage is called proliferative diabetic retinopathy (PDR), where the new vessels grow along the surface of the retina and into the vitreous gel.
These newly formed vessels are highly fragile and abnormal. They are prone to bleeding and causing scar tissue that can pull the retina away from the back of the eye, leading to retinal detachment and rapid vision loss. The most immediate threat to central vision comes from the leakage of fluid into the macula, the small central part of the retina responsible for sharp, detailed vision. This swelling is called diabetic macular edema (DME).
The sustained presence of high glucose levels triggers biochemical pathways that break down the blood-retinal barrier, increasing the permeability of the retinal capillaries. The macula swells as fluid leaks from these compromised vessels, causing the central vision to become blurry or distorted. DME is the primary reason medication must be delivered directly into the eye to stop the leakage and reduce the swelling.
The Treatment: Medications Delivered to the Eye
The medications injected into the eye work by targeting the molecular pathways that cause the vessels to leak and grow abnormally. The central focus of treatment is a protein called Vascular Endothelial Growth Factor (VEGF). High glucose and oxygen deprivation cause the eye to overproduce VEGF, which signals blood vessels to become leaky and stimulates the growth of the fragile new vessels seen in PDR.
The most common treatment involves injecting Anti-VEGF agents, specialized drugs that bind to the VEGF protein. By capturing and neutralizing VEGF, these drugs block its signaling effect. This rapidly reduces the leakage from damaged vessels and slows the growth of new, abnormal vessels. This action helps to dry up the fluid causing the macular edema, often leading to an improvement in central vision.
For some patients, particularly those whose condition involves significant inflammation, specific corticosteroid preparations may be used. These anti-inflammatory drugs are also injected directly into the eye to reduce swelling and leakage by suppressing the inflammatory components of the disease. The medication must be delivered directly into the vitreous humor—the clear, gel-like substance that fills the center of the eye—through a process called an intravitreal injection.
This direct delivery method is necessary because it achieves a high, therapeutic concentration of the drug at the retina where it is needed most. If the medication were taken orally or delivered systemically, it would be diluted throughout the body, making it ineffective in the eye and potentially causing unwanted side effects. Injecting the drug into the vitreous ensures maximum local impact with minimal systemic exposure.
What to Expect During the Injection
While the idea of an eye injection may sound unsettling, the procedure is quick and is performed by a retina specialist in a clinical setting. The process is designed to be comfortable and sterile. It typically begins with the application of numbing anesthetic eye drops or gel to eliminate pain. An antiseptic solution, often an iodine preparation, is then used to clean the surface of the eye and the surrounding area to minimize the risk of infection.
A small instrument called an eyelid speculum is used to gently hold the eyelids open and keep the eyelashes out of the way. The specialist will ask the patient to look in a specific direction while the injection is administered through the white part of the eye, known as the sclera, using an extremely fine needle. The actual injection takes only a few seconds, and most patients report feeling a brief moment of pressure rather than pain.
After the injection, the eye is cleaned, and patients can usually go home shortly after. It is common to experience temporary side effects for a day or two, such as mild irritation, a gritty sensation, or seeing small floaters or specks in the vision. Treatment for diabetic eye disease often requires a series of injections, usually monthly initially, until the macular swelling resolves or the condition is stabilized. Long-term monitoring is necessary because the effects of the medication wear off over time, and regular check-ups determine the need for additional treatments to maintain vision.