Intravitreal injection is the method of administration of drugs into the eye by injection with a fine needle. The medication will be directly applied into the vitreous humor. It is used to treat various eye diseases, such as age-related macular degeneration (AMD), diabetic retinopathy, and infections inside the eye such as endophthalmitis. As compared to topical administration, this method is beneficial for a more localized delivery of medications to the targeted site, as the needle can directly pass through the anatomical eye barrier (e.g. cornea, conjunctiva and lens) and dynamic barrier (e.g. tears and aqueous humor). It could also minimize adverse drug effects on other body tissues via the systemic circulation, which could be a possible risk for intravenous injection of medications. Although there are risks of infections or other complications, with suitable precautions throughout the injection process, chances for these complications could be lowered.
History
Intravitreal injection was first mentioned in a study in 1911, in which the injection of air was used to repair a detached retina. There were also investigations evaluating intravitreal antibiotics injection using sulfanilamide and penicillin to treat endophthalmitis in the 1940s, yet due to the inconsistency of results and safety concerns, this form of drug delivery was only for experimental use and not applied in patients. It was until 1998, that fomivirsen (Vitravene™), the first intravitreal administered medication, was approved by the U.S. Food and Drug Administration (FDA).
In 2004, when Aiello et al. published the first guidelines for intravitreal injection in the journal ‘Retina’, fomivirsen was still the only medication licensed by the FDA for intravitreal injection. At the end of the year, on December 17, the first intravitreal anti-VEGF drug pegaptanib (Macugen) was also licensed by FDA for treatment of wet age-related macular degeneration (wet AMD).
Intravitreal injection has then become more common and a surge in the number of injections performed could be seen. Six extra medications, namely triamcinolone acetonide, ranibizumab (Lucentis), aflibercept (Eylea/Zaltrap), dexamethasone, ocriplasmin and fluocinolone acetonide were approved for this injection by the end of 2014. There are also increasing off-label use of bevacizumab (Avastin) for the management of various ophthalmologic diseases, like AMD, retinal vein occlusion and diabetic macular edema. On top of that, the number of intravitreal injections has escalated from less than 3000 per year in 1999, to an estimation of near 6 million in 2016.
Applications
Intravitreal injection is used to inject a drug into the eye to reduce inflammation (anti-inflammatory), inhibit the growth and development of new blood vessels (angiostatic), or lower the permeability of blood vessels (anti-permeability), in turn curing various eye diseases.
Disorders/diseases that can be treated with intravitreal injection include: Age-related macular degeneration (AMD)/ Macular Degeneration: An eye disorder that slowly destroys sharp, central vision Uveitis: Swelling and inflammation within the eyeball Retinal vein occlusion: A blockage of the veins that carry blood away from the retina, the back part of your eye, and out of the eye Macular edema: Swelling or thickening of the macula (the central area of the retina that provides sharp, central vision) due to abnormal fluid accumulation Diabetic Macular Edema: Poorly controlled diabetes mellitus could lead to diabetic retinopathy, i.e. damages to the retina. The damage to the small blood vessels there causes leakage of fluid Pseudophakic cystoid macular edema Macular edema secondary to retinal vein occlusion Macular edema secondary to uveitis Infections, such as endophthalmitis and retinitis Noninfectious vitritis
Sometimes, an intravitreal injection of antibiotics and steroids is given as part of routine cataract surgery. This avoids having to use drops after surgery.
Common medications used in injection
Antimicrobials
Antimicrobials are intravitreally injected to treat eye infections, such as endophthalmitis and retinitis. The medication used depends on the pathogen responsible for the disease.