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Intravitrial injections

Intravitreal injection (IVI) of a therapeutic substance is the most common procedure performed in ophthalmology. . The diseases treated with this method include diabetic macular oedema (DMO), retinal vein occlusions (RVO), anti-vegf for the treatment of wet macular degeneration and gene therapy for choroideremia and Luxterna for RPE65-mediated inherited retinal dystrophies.

The most effective way to treat wet macula degeneration and several other conditions affecting this part of the eye is place a deposit of a drug close to the site of the disease. At present, this usually means placing the drug in the posterior vitreous. The medication is then held near to the affected area to exert its effect for an extended period so that it can have a maximal and prolonged effect.

The three most commonly used anti-VEGF drugs given by IVI to treat neovascular “wet” AMD, in increasing cost, are Avastin (bevacizumab), ranibizumab (Lucentis); and Eylea (Aflibercept). The cheapest, Avastin is the most commonly used outside the NHS, though technically it is being used “off-label” as its manufacturers have never applied for its use in the eye. Lucentis is made by the same company, is licenced for ocular use and is many times more expensive. There are a multitude of studies that show that Avastin is safe to use and equally effective to Lucentis. The newer compound, Eylea, is more expensive still. It does have a longer effective half life, requiring injections to be performed significantly less often and may have a deeper penetration, useful in treating CNV from choroidal polyps/ polypoidal choroidal vasculopathy (PCV). Not all cases of PCV respond to Anti-VEGF treatment. Often these cases can be treated with photo dynamic therapy (PDT).

In addition to neovascular “wet” AMD, IVI is used extensively to treat diabetic macular oedema and retinal vascular occlusive disease. Additionally, other conditions that can lead to a breakdown in the barrier to retinal invasion by choroidal neovascularisation, such as myopic macular degeneration, angioid streaks and certain forms of choroiditis are often amenable to IVI treatment.

Topical steroids are not effective for significant or chronic macular oedema, though have a place in treating conditions such as cystoid macular oedema following cataract surgery. Systemic steroids can have significant side effects which outweigh the benefits in most cases of macular oedema. The main risks associated with IVI steroids, commonly used in diabetic macular oedema (DMO) and retinal vein occlusion (RVO) are glaucoma and cataract formation.

Additional training is required for drugs such as steroids in suspension or pellet form. Steroids in liquid form such as Kenalog, are normally in a suspension, and require a larger guage needle as the standard size can easily block with the suspended particles. Steroid pellets such as Osurdex and Illuvian carry the greatest risk of all due to their long retention time. Moderate pressure rises can be managed with ocular hypotensive drops. The injector devices used with implants use very large bore needles. Sub-conjunctival lignacaine is the preferred anaesthetic due to its greater potency and the sub-conjunctival bleb makes it easier to ensure that the larger perforation at the injection site through the conjunctiva and through the sclera can made out of alignment and so make bacterial endophthalmitis less likely.

Most of the limited studies on the effect of vitrectomy on pharmacokinetic properties of anti-VEGF drugs in human eyes, indicate that intravitreal drugs have reduced half-lives and increased clearance in vitrectomized eyes, and possibly in pseudophakes especially those having had YAG capsulotomy. There may be an increased role for slow-release steroid implants in vitrectomised eyes .