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A Comprehensive Guide to Intravitreal Injections
A deep dive into precision delivery
London Eye Centres
April 23, 2026
In modern ophthalmology, intravitreal injections are arguably the most significant clinical development of the last two decades. Since the mid-2000s, these injections have transformed visual outcomes for those affected by sight -threatening eye disease.
What is an Intravitreal Injection?
At its simplest, an intravitreal injection is a method of delivering high-dose medication directly to the retina and choroid, bypassing the blood-retinal barrier. Because the eye is a highly protected organ, systemic medications (pills or intravenous drips) often struggle to reach the posterior segment in therapeutic concentrations without causing significant systemic toxicity.
By injecting directly into the vitreous gel of the eye , we achieve a high local concentration of the drug exactly where it is needed, with minimal side effects elsewhere in the body.
How They Work
Most intravitreal injections in the UK fall into two categories: Anti-VEGF agents and Corticosteroids.
1. Anti-VEGF Therapy (The Growth Blockers)
Most sight-threatening retinal diseases involve the overproduction of Vascular Endothelial Growth Factor (VEGF). VEGF is a signalling protein that promotes the growth of fragile new blood vessels which then leak blood into the retina.
Mechanism: Drugs like Ranibizumab (Lucentis), Aflibercept (Eylea), and the newer Faricimab (Vabysmo) act as “molecular sponges.” They bind to VEGF molecule and prevent them from docking with their receptors.
Result: This reduces the growth of new vessels and causes existing leaky vessels to dry up, reducing retinal swelling and scarring.
2. Intravitreal Steroids (The Inflammation Dampeners)
For conditions driven by chronic inflammation rather than just blood vessel growth, steroids (like Dexamethasone or Fluocinolone implants) are used.
Mechanism: These reduce the inflammatory cytokines and stabilise the blood-retinal barrier.
Result: They are particularly effective for long-term oedema (swelling) that doesn’t respond fully to anti-VEGF treatment.
Conditions Treated: The “Big Three”
Condition | Pathophysiology | How Injections Help |
Wet Age-Related Macular Degeneration (nAMD) | Abnormal vessels grow under the macula, leaking fluid and blood. | Anti-VEGF stops the leak and prevents the “disciform scar” that causes permanent central vision loss. |
Diabetic Macular Oedema (DMO) | High blood sugar damages retinal capillaries, causing them to leak fluid into the macula. | Reduces the “soggy” swelling of the retina, restoring the architectural integrity of the macula. |
Retinal Vein Occlusion (RVO) | A “stroke” in the eye’s drainage system causes a backup of pressure and massive fluid leakage. | Clears the fluid (oedema) and reduces the risk of secondary glaucoma. |
The Procedure: Precision in Practice
The procedure is remarkably swift, usually taking less than five minutes. For the patient, the anticipation is almost always worse than the event.
Anaesthesia: The eye is numbed using powerful topical drops or a sub-conjunctival gel.
Asepsis: The eye and eyelids are cleaned with povidone-iodine (Betadine) to minimise the risk of endophthalmitis (internal infection).
The Injection: The needle is inserted through the white of the eye (conjunctiva) and then the pars plana—a "safe zone" roughly 3.5mm to 4mm behind the limbus. This avoids the risk of a retinal tear or lens damage.
Post-Op: The patient is usually given lubricating drops and monitored for a few minutes before being sent home.
Conclusion
Intravitreal injections have turned the tide against some of the most aggressive causes of blindness in the UK. By delivering targeted pharmacology with surgical precision, eye specialists can maintain the structural health of the retina, and ultimately the vision of their patients.
