An intravitreal injection (IVT) is a common, minimally invasive medical procedure that involves delivering medication directly into the eye’s vitreous humor, the clear, jelly-like substance filling the large central cavity. This method ensures high concentrations of the therapeutic agent reach the retina and macula, the light-sensitive tissues at the back of the eye, where many serious vision-threatening diseases originate. The treatment is performed in an office setting and has become a standard approach for managing chronic conditions that would otherwise lead to irreversible vision loss.
Why Direct Delivery is Essential
The eye possesses a sophisticated defense mechanism known as the blood-retina barrier, which is structurally similar to the blood-brain barrier. This barrier is formed by tightly packed cells in the retinal blood vessels and the retinal pigment epithelium, effectively preventing large molecules and many systemic drugs from passing through to the posterior segment of the eye. The intravitreal route bypasses this inherent biological shield, allowing the retina specialist to place a precise and potent dose of medicine exactly where the pathology is occurring. Reducing systemic exposure is important as it dramatically lowers the risk of generalized side effects often associated with widespread drug circulation. The entire process utilizes a fine needle to penetrate the sclera, the white outer layer of the eye, directly into the vitreous cavity.
Eye Conditions Treated
Intravitreal injections are primarily used to manage diseases that cause fluid leakage or the growth of abnormal blood vessels in the retina. The most common condition treated is the “wet” form of Age-related Macular Degeneration (AMD), characterized by the growth of fragile, unwanted blood vessels under the macula. These vessels are prone to leaking fluid and blood, which causes the macula to swell and rapidly degrades sharp central vision. Regular treatment aims to suppress this abnormal vessel activity and dry up the accumulated fluid.
Another major indication is Diabetic Macular Edema (DME), a frequent complication of diabetes where high blood sugar damages the retinal blood vessel walls, causing them to leak fluid into the macula. This leakage leads to swelling and distortion of central vision, making it difficult to read or recognize faces. The injections are also commonly employed for treating Retinal Vein Occlusions (RVOs), which occur when one of the veins draining blood from the retina becomes blocked. When a retinal vein is blocked, blood flow backs up, causing hemorrhages and significant fluid leakage, resulting in severe macular swelling. Injections are also used to deliver antibiotics or antifungals to treat severe eye infections like endophthalmitis.
Medications Administered
The pharmacological agents delivered via IVT fall mainly into two distinct categories, each designed to counteract a specific disease process. The most widely used medications are the Anti-VEGF (Anti-Vascular Endothelial Growth Factor) agents, which include brand-name drugs such as Lucentis (ranibizumab), Eylea (aflibercept), and the off-label use of Avastin (bevacizumab). Vascular Endothelial Growth Factor (VEGF) is a protein naturally produced in the body that signals blood vessels to grow and can also increase their permeability.
In diseases like wet AMD, DME, and RVO, the eye overproduces VEGF in response to inadequate oxygen supply, leading to the formation of abnormal, leaky blood vessels. Anti-VEGF drugs work by binding to and neutralizing this protein, effectively blocking the signal for unwanted vessel growth and reducing fluid leakage from existing vessels.
The second primary category of IVT medication is corticosteroids, which are powerful anti-inflammatory drugs. These are often used to treat macular edema associated with RVOs, DME, and inflammatory conditions like uveitis. Corticosteroids work by suppressing the inflammatory pathways that contribute to fluid leakage and swelling in the retina. Depending on the specific drug, they may be administered as a solution or as a sustained-release implant that delivers a consistent dose of medicine over several months.
The Patient Experience and Aftercare
Before the procedure, the patient’s eye is typically dilated for a thorough examination, and informed consent is reviewed and signed. While the patient does not feel the sharp poke of the needle, they commonly report a brief sensation of pressure or a dull pushing feeling as the medication enters the vitreous cavity.
The Procedure
The procedure begins with the application of topical anesthetic drops or gel to completely numb the eye’s surface, ensuring the patient feels pressure rather than pain during the injection itself. The area around the eye is then meticulously cleaned and sterilized, typically with an antiseptic solution like povidone-iodine, to prevent infection. A small eyelid holder, called a speculum, is often used to keep the eyelids open and prevent blinking while the medication is injected through the pars plana, a thin area of the eye wall just behind the iris. The swift injection into the vitreous takes only a few seconds, and the entire sterile process is completed within minutes.
Immediately following the procedure, patients may notice temporary side effects, such as floating specks or shadows in their vision, which are small air bubbles or the medication itself dispersing in the vitreous. Mild eye discomfort, a gritty or scratchy sensation, and watering are also common, often caused by the antiseptic used to clean the eye. A small red spot on the white of the eye at the injection site, known as a subconjunctival hemorrhage, is a frequent and harmless occurrence that resolves within a week or two. Patients are strongly advised not to rub their eye for the remainder of the day to prevent dislodging the medication or causing irritation. It is also recommended to avoid swimming or getting water directly into the eye for a few days to minimize the risk of infection. Patients are instructed to contact their specialist immediately if they experience worsening or severe pain, sudden vision loss, or increasing redness and discharge, as these could signal a rare complication.